Glass Industry Definitions

We have select Glass Industry definitions below. Click a letter to scroll to all definitions at that letter.


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Abrasion Resistance: The ability to withstand scuffing, scratching, rubbing or wind-scouring.


Absorptance: The ratio of radiant energy absorbed to total incident radiant energy in a glazing system.


Absorption: Transformation of radiant energy to a different form of energy by interaction with matter.


Accelerated Aging: A set of laboratory conditions designed to produce, in a short time, the results of normal aging. Usual factors include temperature, light, oxygen and water.


Acetic Acid / Ethanoic Acid: An acid that can be corrosive to zinc, steel, and other types of aluminized panels. Industrially, acetic acid is used in the preparation of metal acetates, used in some printing processes; vinyl acetate, employed in the production of plastics; cellulose acetate, used in making photographic films and textiles; and volatile organic esters such as ethyl and butyl acetates, widely used as solvents for resins, paints, and lacquers.


Acetone: A colorless, volatile, water-soluble, flammable liquid made from either alcohol or by bacterial fermentation of carbohydrates; used in paints and varnishes, as a general solvent, and in chemical manufacturing.


Acid Embossing / Etching: The process for the decoration of glass involves the application of hydrofluoric acid to the glass surface. Hydrofluoric acid vapors or baths of hydrofluoric acid salts may be used to give glass a matt, frosted appearance similar to that obtained by surface sandblasting, as found in lighting glass. Glass designs can be produced by coating the glass with wax and then inscribing the desired pattern through the wax layer. When applied, the acid will corrode the glass but not attack the wax covered areas.


Acid Polishing: A process used in the production of cut crystal to remove the opacity of etched surfaces where decoration has been applied. Items to be polished are immersed in a mixture of demineralized water, sulphuric acid and hydrofluoric acid, and then rinsed. There may be a single short immersion in a stronger solution or, alternatively, a series of immersions in a weaker solution.


Acid Stamping: The process of acid etching a trademark or signature into glass after it has been annealed, using a device that resembles a rubber stamp.


Acoustic Performance: The ability of a window to attenuate sound transmission in noisy environments, normally expressed as the Sound Transmission Coefficient (STC) in decibels; the ratio of transmitted to incident sound intensity.


Acoustics: The science of sound and sound control.


Acrylic: A noncrystalline thermoplastic with good weather resistance, shatter resistance, and optical clarity; sometimes used for glazing.


Accent Lighting: Directional lighting designed to emphasize a particular object or to draw attention to a part of the field of view.


Adhesion: The clinging or sticking together of two surfaces. The ability of an adhesive to stick to a surface. The property of a coating or sealant to bond to the surface to which it is applied.


Adhesive Failure: Adhesive failure indicated by the material’s failing, such as pulling loose at the surface of the substrate. This is similar to scotch tape peeling off a plastic substrate.


Adhesive: Any substance that is capable of bonding other substances together by surface attachment.


Aerodynamics: The branch of physics that deals with the motion of a solid body through air and other gases.


Aerogel / Transparent Insulation Material: A microporous, transparent silicate foam which has a low thermal conductivity; used as a glazing cavity fill material.


Aging: The progressive change in the chemical and physical properties of a sealant or adhesive.


Air Change Rate: The rate of replacement of air in a space, usually due to infiltration of outdoor air through cracks around windows and doors. Commonly expressed in air changes per hour.


Air Film: The layer of air next to a surface, such as a glass pane, which offers some resistance to heat flow. The R value of a still-air film is about 0.68, while that for the air film associated with a 15-mile-per-hour wind velocity is 0.17.


Air Gap / Air Space: The space in the cavity between two panes of glass in an insulated glass unit.


Air Infiltration: The amount of air leaking in and out of a building through cracks in walls, windows and doors.


Air Leakage: The flow of air which passes through cracks in closed and locked fenestration products.


Air Leakage Rating: A measure of a fenestration systems rate of air leakage in the presence of a specific pressure difference. It is expressed in units of cubic-feet-per-minute per square foot of window area (cfm/sq ft) or cubic-feet-per-minute per foot of window perimeter length (cfm/ft). The lower a windows air leakage rating, the better its airtightness.


Air Quenching: Part of the process of tempering glass, when rapid cooling occurs by blowing air onto both surfaces uniformly and simultaneously.


Air Side / Score Side: The upper surface of the glass.


Air Spacer: Component placed at the perimeter of an insulating glass unit to separate the two lites of glass.


Air Trap / Air Lock: An air filled void, which may be of almost any shape. Air traps in stems are frequently tear-shaped or spirally twisted.


Alcohol: A broad class of organic compounds. In this context they are industrial solvents that include methanol (used in windshield washer fluid), denatured alcohol (used in glass cutting) and isopropyl alcohol (IPA, used as a cleaning solvent).


Alkali Borosilicate Glass: A special glass used for glass-to-metal seals, particularly suitable when electrical qualities are not important.


Allen Wrench: A six-sided wrench.


Alumina Silicate Glass: Alumina (aluminum oxide Al2O3) is added to the glass batch in the form of commonly found feldspars containing alkalis in order to help improve chemical resistance and mechanical strength and to increase viscosity at lower temperatures.


Altitude (Solar): The vertical angular distance of a point in the sky above the horizon. Altitude is measured positively from the horizon to the zenith, from 0 to 90 degrees.


Aluminum: A light, strong, noncorrosive metal that can either be extruded into shapes or used in sheet or coil form and bent into shapes (capping). It has a very high thermal conductivity.


Aluminum Clad Window: Window consisting mainly of wood that is covered externally with aluminum sheet to deter the elements.


Aluminum Spacer: A rectangular or contoured hollow aluminum bar filled with a desiccant (or moisture-absorbing material) traditionally used to separate the panes in double pane glass units.


Alumina Silicate Glass: A special glass used for glass-to-metal seals, particularly suitable when operating temperatures of electrical components are high (up to 750°C).


Ambient Lighting / Task Lighting: Lighting throughout an area for general illumination.


Angular Selective Window: A glazed window whose visible and solar transmittance varies with angle of incidence. For example, high transmittance at near-normal incidence (to retain the view) and low transmittance for high angle of incidence (beam component of sunlight from near the zenith).


Amino Acid Base: A form of chemical cure method of silicone sealant.


Anneal: The controlled process for making glass stronger and less brittle in which the glass is heated and then cooled.


Annealed Glass: Standard sheet of float glass which is heat-treated to increase its impact resistance.


Annealing: Heat treatment that involves the heating of metal, glass or other materials above the critical or recrystallization temperature, followed by controlled cooling to eliminate the effects of cold-working, relieve internal stresses, or improve strength, ductility, or other properties. Under natural conditions, the surface of molten glass will cool more rapidly than the center. This results in internal stresses which may cause the glass sheet or object to crack, shatter or even explode some time later. The annealing process is designed to eliminate or limit such stresses by submitting the glass to strictly controlled cooling in a special oven known as a lehr. Inside the lehr, the glass is allowed to cool to a temperature known as the annealing point. When the glass reaches this point, the lehr temperature is stabilized for a specific length of time (depending on the glass type, its thickness, its coefficient of expansion and the amount of residual stress required) to allow stresses present in the glass to relax. This phase is followed by a period of cooling with a pre-defined temperature gradient.


Annealing Lehr: An in-line controlled heating/cooling apparatus located after the tin bath and before the cooling conveyor of a float glass production line. Its purpose is to relieve induced stress from the flat glass product to allow normal cold end processing.


Anodized Aluminum: Aluminum treated by electrolysis to develop a finished surface (an extremely hard, noncorrosive oxide film). The electrochemical process produces an anodic coating by converting aluminum into aluminum oxide by electrolytic action. The resulting finish may be either clear or colored and is an integral part of the aluminum.


Anodizing: A method of coating, coloring and finishing aluminum that both protects and beautifies the aluminum.


Anti-Glare Coating: A treatment applied to a glazing system to reduce the amount of unwanted diffuse visible transmittance.


Anti-Lacerative Glass: Glass that has a resilient layer of polyvinyl butyral (PVB) added to the inner surface.


Anti-Reflective Coating: A transparent coating, typically 150 nm thick, which reduces surface reflectance by using destructive interference between light reflected at the substrate surface and light reflected at the coating surface.


Anti-Walk Blocks: Elastomeric blocks that limits lateral glass movement in the glazing channel, which may result from thermal, seismic, wind load effects, building movement and other forces that may apply.


Architectural Scale: A ruler marked in scaled increments used to measure a scaled drawing.


Arch Top: One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening. Also referred to as circle-heads, circle-tops and round tops.


Argon Gas / Argon Filled: An inert, nontoxic gas placed between glass panes in insulated glass units in order to improve the insulating value of sealed glass units.


Armor Plate Glass: Laminated glass resistant to mechanical shock composed of at least four panes of glass and usually at least 25 mm thick.


Aspect Ratio: The quotient of the long side of a glazing lite over the short side of that lite.


Astragal: Center post between two swinging doors. A convex molding or wooden strip across a surface or separating panels, typically semicircular in cross-section.


Atrium: Traditionally, the central space of a building open to the sky usually multistory and glazed. An atrium differs from a court, also an outdoor area which is surrounded partially or entirely by buildings or walls.


Attenuation: The sound reduction process in which sound energy is absorbed or diminished in intensity as the result of energy conversion from sound to motion or heat.


Autoclave: A strong vessel used for the lamination of glass under huge pressure and controlled temperature conditions.


Awning: A window with sash swinging outward from bottom. A sheet of canvas or other material stretched on a frame and used to keep the sun or rain off a storefront, window, doorway, or deck.


Awning Window: A window with a sash hinged at the top, which projects outward from the plane of the frame.


Azimuth (Solar): Compass bearing, relative to true (geographic) North, of a point on the horizon. The horizon is defined as a huge, imaginary circle centered on the observer. Bearings are measured clockwise in degrees from North, ranging from 0 degrees (North) through 90 (East), 180 (South), 270 (West), and up to 360 (North again).


AZS Refractories: Refractory blocks or tiles in varying proportions of alumina-zirconia silica; initially used for areas where corrosion resistance was important but now used in most parts of the furnace.




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Backbedding: Material or compound used to seal the glass to a window sash.


Backer Rod: A compressible material, either open or closed cell, placed into voids between materials to insulate and allow a backing for the application sealant.


Back Up: A material placed into a joint to control the depth of the sealant and to prevent adhesion at the base of the sealant bead.


Balance: Mechanical device (normally spring loaded) used in single and double hung windows as a means of counterbalancing the weight of the sash during opening and closing.


Banding: The application of decorative bands of enamel or precious metal compounds, normally by machine, to containers such as tumblers, cups, cosmetics bottles, etc.


Barium Crown Glass: Barium crown glass contains larger proportions of boron oxide and barium oxide with a relatively low SiO2 content. The glass can be stabilized against devitrification and weathering by adding small amounts of substances such as aluminum oxide.


Baroque Pattern: Wire glass where the pattern is square and wires are parallel with the edges of the sheet.


Batch: A term used to refer to the raw materials required to produce the desired type of glass once they have been weighed and mixed and are ready for melting. A quantity of raw materials mixed in proper proportions and prepared for fusion into glass, also called frit.


Bay: A combination of window units that projects to the exterior. Usually features a large center unit with two flanking units at 30° or 45° angles to the wall.


Bead: A sealant or adhesive compound after application in a joint, irrespective of the method of application. A bead looks like a ribbon of adhesive rather than a round drop of adhesive.


Bed or Bedding: In glazing, the bead of compound or sealant applied between a lite of glass or panel and the stationary stop or sight bar of the sash or frame. It is usually the first bead of compound or sealant to be applied when setting glass or panels.


Bedding of Stop: In glazing, the application of compound or sealant at the base of the channel, just before the stop is placed in position, or buttered on the inside face of the stop.


Bent Glass: Flat glass that has been shaped while hot into curved shapes.


Bending: A process used widely in the production of bowls, plates, ashtrays, etc., whereby the shaped glass article (which may be pre-printed) still in sheet form is placed on a stainless steel, sheet steel or cast iron mould coated with talc or powdered chalk. The temperature is increased until the glass sheet sinks into shape in the mold.


Bevel of Compound Bead: In glazing, a bead of compound applied to provide a slanted top surface so that water will drain away from the glass or panel.


Beveling: The production, by abrasion, of a sloping edge on the glass sheet. Commonly used on mirror glass.


Bezel: A curved, tapered, decorative cover located behind the door latch or in the well of a door pull.


Bit Brace: A hand tool used to drill holes.


Bite: The dimension by which the framing system overlaps the edge of the glazing infill.


Black Edge: If the backing of a mirror deteriorates, the silver turns black.  This condition is known as black edge.


Bleeding: A migration of a liquid to the surface of a component or into/onto an adjacent material.


Blinding Glare: Glare so intense that, for an appreciable length of time after it has been removed, no object can be seen.


Blisters: A profusion of bubbles in a coating film that form during the heat treating process and remain after the film solidifies.


Block (Setting): A small piece of neoprene or other suitable material used to position the glass in the frame or opening. Rectangular, cured sections of EPDM, neoprene, silicone or other suitable material, used to position the glass product in the glazing channel.


Blow-and-Blow Process: In the blow-and-blow process, the glass is first blown through a valve in the baffle, forcing it down into the three piece ring mold which is held in the neckring arm below the blanks, to form the finish (the term finish describes the details (such as cap sealing surface, screw threads, retaining rib for a tamper-proof cap, etc) at the open end of the container.) The compressed air is blown through the glass, which results in hollow and partly formed container. Compressed air is then blown again at the second stage to give final shape.


Blowpipe: An iron or steel tube, usually about five feet long, for blowing glass. Blowpipes have a mouthpiece at one end and are usually fitted at the other end with a metal ring that helps to retain a gather.


Bond Strength: The force, per unit area, necessary to rupture a bond.


Bond: The attachment at an interface between substrate and adhesive or sealant.


Borate Glass: A glass whose essential glass former is boron oxide rather than silica.


Borosilicate Glass: Glass made from silica and boric oxide. Such glass is highly resistant to chemical corrosion and temperature change (thermal shock) and is particularly suitable for laboratory ware (test tubes, etc), domestic cooking ware (oven dishes, etc), high-power lamps and other technical glass ware. It is also used when glass has to be bonded to metal and low expansion is a key characteristic.


Bottom Rail: The bottom horizontal member of a window sash or door panel.


Boudin Process: A glass rolling process in which glass flow is controlled by the speed of the machine and fed directly onto the rollers over a refractory sill. As the ribbon of glass passes from the forming rollers, it is supported by an air cushion. The process can be adapted in order to introduce wire mesh into the glass ribbon.


Bow / Warp: A combination window that projects to the exterior. Usually features four or more window units in a radial or bow formation. A curve, bend or other deviation from flatness in glass.


Box Bay: A combination of window units that projects to the exterior. Usually features a large center unit with two flanking units at 90 degree angles to the wall.


Breaking Stick: A stick or other material used to place under the score of glass or plastics that assists in the breaking of the material.


Breather Tube Units: Tube placed through airspacer and seal of insulating glass that allows unit to accommodate changes in pressure between time and location of manufacture and time and location of installation, where it is sealed. Usually used to accommodate changes in altitude between plant and job site. An insulating glass unit with a tube and/or hole factory-placed into the unit’s spacer to accommodate pressure differences encountered in shipping due to change in elevation. The tube and/or hole are to be properly sealed on the jobsite prior to unit installation.


Brickmould: A type of external casing for windows and doors.


Brightness: The subjective perception of luminance.


Brise-Soleil: An architectural device on a building (such as a projection, louvers, or a screen) that blocks unwanted sunlight.


British Thermal Unit (BTU): An abbreviation for British Thermal Unit – a standard measure of the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit.


Bug: The ANSI insignia on laminated and tempered glass.


Building Envelope: The outer elements of a building, both above and below ground, that divide the external and internal environments.


Building Information Modeling (BIM): A 3-D, object-oriented approach to computer aided architectural design. Enables data for manufacturer’s details to be imported right into project design and presents 3-D models of products in place in building. Also provides access and ability to add to detailed imagery and information to everyone involved in the building process and building operations after project completion.


Building Integrated Photovoltaics (BIVP): A term used for products, such as commercial glazing, with solar power collection cells built in.


Bubbles: Gaseous inclusions in the glass melt which are removed by refining. Fining agents are introduced to encourage the formation of larger bubbles which rise more rapidly to the surface of the melt, attracting smaller bubbles on their way. Larger bubbles which are not removed by fining are known as blisters, smaller ones as seeds and longitudinally stretched bubbles as air-lines. Bubbles in glass are generally considered as defects but may also be intentionally created and used as a form of decoration.


Bubbling: Open or closed pockets in a sealant caused by release, production or expansion of gasses.


Bulb Edge: In float glass manufacture, the extreme lateral edge of the ribbon as drawn.


Bullet Proof Glass: Armor plate glass which is more than 60 mm thick and resists penetration by bullets.


Bullet Resistant Glass: Glass that consists of multiple layers of laminated glass. It is designed to resist penetration from medium to super powered small arms and high powered rifles.


Bull’s Eye: Impact damage to laminated glass that is marked by a clean, separated cone in the outer layer of the glass.


Burners: Used to heat glass in furnaces of all sizes, burners mix air or oxygen and gas (natural gas or liquid petroleum gases) for efficient combustion.


Bushings: Platinum alloy electrically heated boxes with numerous nozzles in their bases used as furnaces for the forming of continuous glass fiber. Glass can be fed into the heated bushing either in its molten state from a forehearth (direct melt) or, alternatively, as marbles to be melted (re-melt process).


Buttering: The application of sealant to the surface of substrate before placing another substrate in position.


Butt Glazing: The installation of glass products where the vertical glass edges are without structural supporting mullions.


Butyl Dam: Butyl Tape Kits have been used as positioning dams. Other terms for a butyl dam are: Sealant Dam, Tape Kit.


Butyl Rubber: A copolymer of isobutene and isoprene. As a sealant, it has low recovery and slow cure, but good tensile strength and elongation.


Butyl: A petroleum adhesive product that requires no curing or hardening. Butyl is available in rolls of approximately 15 feet. Sometimes called Butyl Tape Kit or Tape Kit. It is available in various thicknesses and shapes.




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Cap Bead: A finished bead applied at the top of an installation.


Capillary Tube Units: Tube placed through airspacer and seal of insulating glass that allows unit to accommodate changes in pressure between time and location of manufacture and time and location of installation, where it is sealed. Usually used to accommodate changes in altitude between plant and job site. Also referred to as breather tube. An insulating glass unit with a very small inside diameter metal tube of specific length factory-placed into the unit’s spacer to accommodate pressure differences encountered in shipping because of substantial changes in elevation and the pressure differences encountered daily after installation. Capillary tubes may or may not require sealing prior to installation.


Capstock: A material co-extruded with PVC formulated to offer a specific color, finish and/or function, such as heat resistance.


Carbide: A hard binary compound of carbon and a more electropositive element.  Used to coat and reinforce the tips of tools to extend the life of the tool.


Casement: A window sash which swings open on side hinges. Window with sash cranking outward, to the right or left.


Casing: Exposed molding or profile around a window or door, on either the inside or outside, to cover the space between the window frame or door jamb and the wall.


Casement Window: A window containing one or more side-hinged sashes hinged that project outward or inward from the plane of the window in the vertical plane. A conventional casement window in North America swings outward and in Europe it swings inward.


Casting: A process of shaping glass by pouring hot glass into/onto molds or tables.


Cast Glass: Glass produced by casting. Pouring molten glass into a mold or by heating glass already contained in the mold until the glass melts and assumes the shape of the mold.


Catalyst: The substance added in small quantities to promote a reaction, while remaining unchanged itself.


Cathedral: The name of the texture or a type of art glass.


Caulk / Caulking Compound: A mastic compound for filling joints and sealing cracks to prevent leakage of water and air; commonly made of silicone, bituminous, acrylic or rubber-based material. A sealant with a relatively low movement capability.


Caulking: Filling joints, cracks, voids, or crevices with a sealant in order to prevent the passage of air or water. A resilient mastic compound often having a silicone, bituminous, or rubber base; used to seal cracks, fill joints, prevent leakage, and/or provide waterproofing.


Cell Cast: A method of manufacturing plastics, where molten plastic is poured between two sheets of glass and allowed to cure.


Cellular PVC: Extruded polyvinyl chloride material used in window and door components and trim. Unlike rigid or hollow vinyl, it features a foam or cell structure inside. It can often be nailed, sawn and fabricated like wood.


Cellulosic Composite: Generally, a material combining an organic material, such as wood fiber, extruded with a plastic.


Centrifugal Force: The force that tends to make an object go outward from a center of rotation.


Centrifuging Process: A relatively new method for the production of hollow ware such as borosilicate glass columns in chemical plants, funnels, television tubes and other non-rotationally symmetrical items by spinning. Molten glass is fed into a steel mould which rotates at the required speed. At high speeds, the glass can assume almost cylindrical shapes. When the glass has cooled sufficiently, rotation stops and the glass is removed.


Ceramic Glass Enamel: A vitreous inorganic coating bonded to glass by fusion at a temperature generally above 500 degrees Celsius.


Chalcogenide Glass: Glass with electrical conductivity characteristics made with the addition of the chalcogen elements such as sulphur, selenium and tellurium.


Channel Tape: A cork and rubber composition material used to secure door glass and to fill channels.


Channel: A piece of U-shaped metal lined with felt used to reduce glass breakage and noise, and to correct alignment of moveable glass parts.


Channel Glazing: The installation of glass products into U-shaped glazing channels. The channels may have fixed stops, however, at least one glazing stop on one edge must be removable.


Channel Width: The distance between opposing glazing stops.


Checks: Very small cracks in flat glass, usually at the edge.


Check Rail / Meeting Rail: The bottom rail on the upper sash and the upper rail of the lower sash of a double hung window unit, where the lock is mounted.


Chemical Cure: Curing by chemical reaction. This usually involves the cross-linking of a polymer.


Chemically Strengthened Glass: Glass that has been strengthened by ion exchange to produce a compressive stress layer at the treated surface.


China Markers: A wax marker used to mark glass.


Chip: Damage to the surface of the glass not associated with other types of damage. Impact damage to laminated glass that does not penetrate the outer lite. Although glass is missing from the impact point, there is no trapped air in the damage.


Chipped Edge: An imperfection due to breakage of a small fragment from the cut edge of the glass. Generally, this is not serious except in heat absorbing glass.


Chromogenic Glazing: A broad class of switchable glazing including active materials (e.g. electrochromic) and passive materials such as photochromic and thermochromic.


Circle Cutters: Cutters that have a vacuum base that attaches directly to the glass.  The adjustable arm holds a ruler set to the radius of the desired circle.


Circle Top: One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening. Also referred to as arch tops, circle heads, and round tops.


Cladding: Material placed on the exterior of wood frame and sash components to provide ease of maintenance. Common cladding materials include vinyl and extruded or roll formed aluminum.


Clear Glass: Architectural clear glass is mostly of the soda-lime-silica type, and composition varies between manufacturers, but is generally 70–74 percent silica, 5–12 percent lime, and 12–16 percent soda, with small amounts of magnesium, aluminum, iron and other elements.


Clerestory: That part of a building rising clear of the roof or other parts whose walls contain windows for lighting the interior.


Clerestory Window: A venting or fixed window positioned above other windows or doors on an upper outside wall of a room. A window in the upper part of a high ceilinged room that admits light to the center of the room.


Clips: Devices used on the fixed panels of shower glass panels and headers are used for safety and support reasons on top of the glass.


Coated Glass: Glass with a chemical film applied to one surface. The film can provide enhanced performance characteristics such as privacy, solar or mirror effects.


Coating: A thin layer which covers the surface of an object. Coatings may be applied to glass in order to alter the appearance or performance of the product in question e.g. anti-reflective coatings applied to auto mirrors to aid vision, coatings with photocatalytic and hydrophilic properties to make self-cleaning windows.


Cohesion: The ability of a sealant or adhesive to hold itself together; the internal strength of an adhesive or sealant.


Cohesive Failure: Adhesive failure indicated by hardened material on both substrate surfaces. The material itself failed (the body of the adhesive or sealant pulled apart).


Cold End: The name given to the stage in glass production involving processing when the glass is cold. Cold end processes include grinding, engraving, cutting, etc.


Color of Transmitted Light: The human eyes and brains subjective interpretation of the spectral distribution of transmitted visible radiation. Transmitted light is said to be colorless (white) if it matches the spectrum of the external incident light, while any imparted color is due to the subtraction of the complementary wavelengths by absorption or reflection of those wavelengths by the glazing system.


Combination Door: A screen or storm door used in combination with a primary door. Storm windows also are referred to as combination windows.


Combustible: Any liquid that will ignite at or above 100°F, but below 200°F.


Commercial Entrance System: Products used for ingress and egress in nonresidential buildings. Commercial entrance systems typically utilize panic hardware, automatic closers, and relatively large amounts of glass.


Compatibility: Refers to the reaction a sealant has on another sealant or on another material.


Composite: A term used for window or door components that consist of two or more materials, such as glass fibers or wood and plastic. The term also is used for windows and doors that combine two or more materials in the frame or sash construction, such as a product with a wood interior and a vinyl or aluminum exterior.


Composite Frame: A frame consisting of two or more materials – for example, an interior wood element with an exterior fiberglass element.


Compress: The act of pressing together or to force into a smaller space.


Compression Gasket: A system that uses a soft gasket on one side of the glass and a firm, dense gasket called a wedge on the other.


Compression Set: Occurs when a sealant is crushed and does not return to its original dimension when the load is removed.


Compression: Pressure exerted on a sealant in a joint.


Compound: A chemical formulation of ingredients used to produce caulking, elastomeric joint sealant, etc.


Condensation: The deposit of water vapor from the air on any cold surface whose temperature is below the dew point, such as a cold window glass or frame that is exposed to humid indoor or outdoor air. Water vapor from the air deposited on any cold surface that has a temperature below the dew point. Sometimes a problem on cold (and poorly insulated) window glass or framing that is exposed to humid indoor air.


Condensation Resistance: Condensation Resistance index; an indication of a windows ability to resist condensation developed by NFRC. The higher the CR, the less likely condensation is to occur.


Condensation Resistance Factor (CRF): Condensation Resistance Factor is an indication of a windows ability to resist condensation developed by AAMA. The higher the CRF, the less likely condensation is to occur.


Conduction: Transfer of heat through a material via molecular contact; heat flows from a higher temperature area to a lower temperature one.


Conductivity, Thermal: The time rate of steady state heat flow through a unit area of homogenous material induced by a unit temperature gradient in a direction perpendicular to that unit area.


Conductive Coating: A glass coating which is electrically conductive. Conductive coatings have been used to produce frost-free windscreens, and in a range of electro-optical applications. One way of producing a conductive coating is by depositing tin salts onto the glass.


Consistency: Degree of softness or firmness of a compound as supplied in the container and varying according to method of application, such as gun, knife, tool, etc.


Containers, Defects: Defects in automatically produced containers are categorized as Very critical Group 1 defects make the container dangerous and unusable, Main faults – Group 2 defects make the container unusable; Group 1 and 2 defects must be discarded, and Secondary – Group 3 defects represent a lowering of the quality of the container but do not affect the functionality of the container.


Containers, Enameling: The application of enamel as a means of applying decoration and/or labeling to containers. Enamel patterning or labeling is typically applied by automated silk screening; all-over color can be applied by spraying.


Containers, Forming: The process of turning a gob of molten glass into a hollow container was first mechanized towards the end of the 19th Century. Fully automatic machines were developed during the first quarter of the 20th Century, principally in the USA, using the blow-and-blow process for narrow-neck ware and the press-and-blow process for wide-neck ware. The landmarks in the development of automatic forming of containers were the gob feeder in 1923, which automated delivery of consistently sized gobs of glass, and the individual section bottle making machine in 1925. The equipment in use today is descended from these innovations.


Containers, Inspection: Inspection of glass containers includes the following: gauging or measuring; inspection for specific faults; proof testing. Gauging or measuring checks: height, diameter and verticality; choke (inner and outer dimension of the neck); dips and saddles in the finish area (mouth/seal of the container); wall thickness. Inspection for specific faults: cracks (also known as checks); stones; foreign material (tramps); spikes; birdswings; thin spots. Proof testing: simulated impact; vertical load.


Contaminant: A substance, liquid or solid, which is present in a break. Contaminants must be removed from a break before a repair can begin.


Continuous Cast Plastic: A method of manufacturing plastics, where molten plastic is forced through a machine, then cooled and dried on stainless steel rollers.


Convection: A heat transfer process involving motion of a fluid, such as air, caused by either the difference in density of the fluid and the action of gravity (natural convection) or by mechanical forces such as blowers, fans, etc. (forced convection). Convection affects heat transfer from the surface to air, whether it is for enclosed spaces (like insulated glazing unit cavity) or open spaces (like indoor glass surface to room air).


Coolant: A liquid used to cool and lubricate glass while it is being cut or ground with a tool to prevent hot spots or fracturing of the glass.


Cool Daylight Glazing: Spectrally selective glazing that employs tinting and/or surface coatings to achieve a visible transmittance that exceeds the solar heat gain coefficient (total solar energy transmittance).


Corner Cleaner: Machine that removes the bead of excess material formed in welding vinyl window corners.


Corrosion: The chemical reaction of air, moisture, or corrosive materials on a surface; also called oxidation. The process of wearing away the surface of a solid.


Cosmetic Blemish: A defect in the appearance of any material.


Cosmetic Surface: A surface that is finished or decorated to improve its appearance. Includes such things as paint, glass and upholstery.


Cottage Double Hung: A double hung window in which the top sash is shorter than the bottom sash.


Crazing: A phenomena that occurs to plastic when it is exposed to either harsh weatherization, UV light or force bending beyond the recommended minimum radius.


Creep: The deformation over time of a body under constant load.


Cristallo: An extremely clear glass developed by Venetian glass-makers by adding manganese (as a decolorizer) to the batch.


Critical Path Method: (CPM) is a step-by-step technique for process planning that defines critical and non-critical tasks with the goal of preventing time-frame problems and process bottlenecks.


Cross-Linked: Molecules that are joined side by side as well as end to end.


Crown Glass: Large panes that first became available in the seventeenth century and were incorporated in wooden sash windows. The glass was hand-blown through a pipe (pontil) into a circular disc, leaving a bubble or bullion where the pipe was inserted. Also known as bottle glass or bull’s eye glass.

  1. Window glass blown into a crown or hollow globe that is flattened and cut before use. This is produced by reheating and spinning out a bowl-shaped piece of glass (bullion) that causes the glass to extend into a flat disk by centrifugal force. The glass is then cut into the size required
  2. One of the two principal types of optical glass used in the production of compound lenses. The Crown glass, which is an alkali-lime silicate optical glass, has a low index of refraction and low dispersion (its Abbe v-value is larger than 50 or 55, depending on its index).


Crush: A lightly pitted area on glass resulting in a dull grey appearance.


Crystal: Three-dimensional building blocks that make a substance internally rigid.


Cullet: Broken glass, excess glass from a previous melt or edges trimmed off when cutting glass to size. Cullet is an essential ingredient in the raw batch in glass-making because it facilitates melting.


Cure Time: The time required for a chemical or material to dry or set at a given temperature and humidity. Cure times vary with the type of material used and the thickness of the application.


Cure: The hardening of a liquid material or adhesive by means of a chemical reaction. A process of drying and hardening over a given period.


Curing Agent: A chemical which is added to effect a cure in a polymer.


Curing by Chemical Reaction: This usually involves the cross-linking of a polymer.


Curtain Wall: An external non-load bearing wall, applied in front of a frame structure, thereby bypassing floor slabs. The cladding is intended to separate the internal and external environments and is distinct from the building structure. There are now many curtain walls systems manufactured from a variety of materials; the systems typically include both windows and spandrel sections.


Cutter: Tool used in cutting glass.


Cutting: The technique whereby glass is removed from the surface of an object by grinding it with a rotating wheel made of stone, wood, or metal, and an abrasive suspended in liquid.


Cut-Running Pliers: Pliers designed for use parallel to the score.  The upper jaw has two projections that taper outward from the center.


Cut Sizes: Glass cut to specific width and length.


Cutting Jig: A device used to standardize the cutting of similar size and length materials.


Cutting Rake: The angle and shape of the tip of a cutting tool, such as a drill bit or a saw blade.


Cylinder Glass: A glass that is blown in the shape of a cylinder and flattened into a sheet. A technique for producing sheet glass dating from the 11th century. Molten glass blown into a cylinder and cut apart, then reheated and flattened. By blowing a hollow glass sphere and swinging it vertically, gravity pulls the glass into a cylindrical pod measuring up to 3 meters long, with a width of up to 45 cm. While still hot, the ends of the pod are cut off and the resulting cylinder cut lengthways and laid flat.


Cylinder: Subassemblies for a door lock containing a cylinder plug with keyway and a cylinder body with tumbler mechanisms.




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Dalle Glass: Colored glass produced in pot furnaces and cast in molds to form plates in thicknesses of approximately 25 cms. Dalle glass (French for tile) is used in churches and decorative glazing, as well as for furnishings such as door handles.


Damage: A break in laminated glass. Same as break and crack.


Danner Process: A widely used method for the production of glass tubing. The process was developed by an American engineer, Edward Danner, in 1912. In the Danner process, the glass flow falls onto a rotating, slightly downward pointing mandrel. Air is blown down a shaft through the middle of the mandrel, thus creating a hollow space in the glass as it is drawn off the end of the mandrel by a tractor mechanism. The diameter and thickness of the glass tubing can be controlled by regulating the strength of the air flow through the mandrel and the speed of the drawing machine.


Dauber: A disposable cotton applicator for applying primers and preps to the metal and glass bonding surfaces.


Daylight Distribution: The distribution of illuminance due to sunlight and sky light within a room, generally measured on a horizontal plane at typical work plane height (0.8 m, or 2.5 feet above the floor). Units: lux (lx=lm/m2) or footcandles (fc) where 1 fc=10.764 lx.


Daylight Factor: The ratio, in percent, of work plane illuminance at a given point to the outdoor illuminance on a horizontal plane. It is only evaluated under cloudy sky conditions (no direct solar beam).


Daylighting: A building energy conservation measure involving the deliberate displacement of artificial lighting by dispersed sunlight or diffuse sky light. Switching, dimming, or other light control strategies must be employed. The mere admission of natural light without a compensating reduction in electric lighting density will not result in a net energy or environmental benefit, although it might improve visual amenity.


Day Tank: A glass-containing vessel made from refractory blocks mainly used for the melting of batch for colored glass, crystal glass and soft special glasses. Day tanks are refilled with batch daily, with melting usually done at night and glass production the following day. Used for producing larger quantities of glass than is possible with pot furnaces. The type of glass to be melted can be changed at short notice.


Debridge: The process of cutting away the metal on the bottom of a thermal break cavity once the two part polyurethane has reached full strength, thus creating a thermally broken extrusion.


Decibel: A unit for expressing the relative intensity of sounds on a scale from 0 for average least perceptible sound to about 130 for the average pain level.


Decorative Glass: Art glass; cathedral, stained or patterned glass.


Deflection (framing member): The amount of bending movement of any part of a structural member perpendicular to the axis of the member under an applied load.


Deflection (center of glass): The amount of bending movement of the center of a glass lite perpendicular to the plane of the glass surface under applied load.


Delamination: The failure of the bond between layers, as when glass separates from the laminate.


Demand Flow Technology (DFT): An approach to analyzing and optimizing production lines.


Desiccant: An extremely porous crystalline substance (hygroscopic or water-absorbing) used in granulated or bulk form inside the spacer of an insulating glass unit in order to keep the gas(es) within the sealed space dry and prevent condensation and fogging.


Design Pressure: Specified pressure a product is designed to withstand.


Denatured Alcohol: Denatured alcohol is ethanol (ethyl alcohol) made unfit for human consumption by adding one or more chemicals (denaturants) to it. Denaturing refers to removing a property from the alcohol (being able to drink it), not to chemically altering or decomposing it, so denatured alcohol contains ordinary ethyl alcohol.


Density: The mass per unit volume of a substance under conditions of pressure and temperature.


Design Heat Loss: The calculated values, expressed in units of BTU per hour (abbreviated BTU/h), for the heat transmitted from a warm interior to a cold outdoor condition under prescribed extreme weather conditions. The values are useful for selecting heating equipment and estimating seasonal energy requirements. Infiltration heat loss is a part of the design heat loss.


Design Life: The period of time during which a system or component is expected to perform its intended function, without significant degradation of performance and without requiring major maintenance or replacement.


Design Pressure (DP): The wind-load pressure to which a product is tested and rated to withstand.


Design Wind Load: The wind-load pressure a product is required by the specifier to withstand in its end use application.


Dewpoint (temperature): The temperature at which water vapor in air will condense at a given state of humidity and pressure.


Diamond Cutters: Specially shaped diamond to score glass.


Diffuse Light: Lighting on a work plane or object that is not predominantly incident from any particular direction.


Diffusing Glass: Glass with an irregular surface for scattering light; used for privacy or to reduce glare.


Diffuser: A translucent glazing layer or window accessory designed to intercept direct-beam radiation and transmit it diffusively (i.e. in many directions at the same time); also provides privacy.


Diffusivity, Thermal: Thermal conductivity per unit of heat capacity.


Digs: Deep short scratches.


Ding: A non-technical term often used by the public to refer to a stone damage to laminated glass.


Direct Glare: Glare resulting from high illuminance or insufficiently shielded light sources in the field of view. Direct glare is usually associated with bright areas, such as the sky, that are outside the visual task or region being viewed.


Direct Sunlight / Beam Sunlight: Daylight directly from the sun without any diffusion.


Disability Glare: Glare resulting in reduced visual performance and visibility. Often accompanied by discomfort glare.


Discomfort Glare: Glare producing discomfort. It does not necessarily interfere with visual performance or visibility.


Distortion: The optical effect due to the variation of sheet glass thickness. Alteration of viewed images caused by variations in glass flatness or inhomogeneous portions within the glass. An inherent characteristic of heat treated glass.


Divided Light: A window with a number of small panes of glass separated and held in place by muntins. Separately framed pieces or panes of glass. A double hung window, for instance, often has several lites divided by muntins in each sash. These designs are often referred to as six-over-six, eight-over-one, etc, to indicate the number of lites in each sash. Designs simulating the appearance of separately framed panes of glass are often referred to as SDLs or simulated divided lites. Designs using actual separate pieces of glass are sometimes referred to as TDLs or true divided lites.


Division Bar: A vertical run channel located between the door window and vent glass.


DOE2.1E: A building-simulation computer program used to calculate total annual energy use.


Doghouse: The name used to describe the batch feeding compartment within the furnace. The molten glass is covered with the batch material as it flows through the compartment.


Dolomite: A raw material compound (CaCO3 + MgCO3) of calcium carbonate and magnesium oxide, which helps lower the melting temperature in the production of flat glass.


Domestic Ware: The collective term for glass containers used in the home (oven dishes, bowls, jars, etc).


Dormer: An area protruding from the roof of a house, generally featuring one or more windows.


Double Envelope: A facade comprised of a pair of skins separated by an air space, which acts as a buffer against temperature extremes, wind and sound. The cladding can be designed into a multiple permutations of solid and diaphanous members, operable or fixed. Sun shading devices are often located within the cavity. The system goes by many names, including Double Leaf Facade, Double Skin Facade and Ventilated Facade.


Double Glazing: In general, any use of two layers of glass separated by an air space within an opening to improve insulation against heat transfer and/or sound transmission. In factory made double glazing units, the air between the glass sheets is thoroughly dried and the space is sealed airtight, eliminating possible condensation and providing superior insulating properties. It also allows for between glass shading options such as muntins, blinds, and pleated shades.


Double Glazing Unit: Two panes of glass separated by a permanently sealed cavity.


Double Seal Units: Insulating glass with two materials used to form the seal of the glass.


Double Hung Window: A window consisting of a pair of vertical sliding sashes with either sash opening independently of the other. It can use either a counterbalance mechanism to hold the sash in place or spring loaded side bars that keep sash in place by friction.


Double Strength Glass: Glass between 0.115 and 0.133 inch thick.


Drawn Glass: Glass made by a continuous mechanical drawing operation. A process for making sheet glass by drawing the molten glass as a sheet directly from the furnace. The thickness of the glass is determined by the drawing rate.


Drilling: The use of a drill to gain access to a tight break.


Drill Cap: Molding placed on top of the header brickmold or casing of a window frame.


Drip: A projecting fin or a groove at the outer edge of a sill, soffit, or other projecting member in a wall, designed to interrupt the flow of water downward over the wall or inward across the soffit.


Drop-Jaw Glass Pliers: Pliers used for breaking glass. They have a flat upper jaw and humped lower jaw.


Dry Glazing: Also called compression glazing, a term used to describe various means of sealing monolithic and insulating glass in the supporting framing system with synthetic rubber and other elastomeric gasket materials.


Dry Seal: Accomplishment of weather seal between glass and sash by use of strips or gaskets of Neoprene, EPDM, silicone or other flexible material. A dry seal may not be completely watertight.


Dual Seal Unit: A sealed multiple pane glazing unit with two independent materials used in the edge seal for bonding the glass layers to the spacer. The dual seal reduces the possibility of mechanical failure (i.e., separation of glass from spacer and loss of dry air or other gas(es) used in the cavity).


Durometer: The measurement of hardness of a material. A gauge to measure the hardness of an elastomeric material.


Dynamic Glazing: See Switchable glazing.




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EPDM: Ethylene Propylene Diene Monomer, a synthetic rubber.


Edge Block: See Anti-Walk Block


Edge Clearance: Nominal spacing between the edge of the glass product and the bottom of the glazing pocket (channel).


Edging: The shaping or finishing of the edges of a glass surface, usually by grinding with an abrasive wheel.


Edge Effect: Heat transfer at the edge of an insulating glass unit due to the thermal properties of spacers and sealants.


Egress Window: A window providing egress, as defined in applicable building codes. Also referred to as emergency exit window, escape window, and fire-escape window.


Egress: A path or means of going out of a building or structure exit.


Effective Thermal Conductivity: The combined effects of conduction, convection, and radiation in fluid-filled (gas-filled) enclosures and cavities, converted into an apparent or effective conductivity of a solid.


Elastomer: An elastic, rubber-like substance, such as natural or synthetic rubber.


Elastomeric: Having the property of returning to its original shape and position after removal of load. An elastic rubber like substance.


Electrochromic(s) Glazing: Glazing with optical properties that can be varied continuously from clear to dark with a low-voltage signal. Ions are reversibly injected or removed from an electrochromic material.


Electromagnetic Spectrum: Radiant energy over a broad range of wavelengths.


Electrode: A metal conductor through which electricity enters or leaves an electrolyte, gas, vacuum, etc.


Embossing: Carving or molding in relief. The forming or application of figures or patterns to an object so that they stand out from the surface.


Emery: A granular mineral substance used for grinding and polishing glass.


Emissivity: The relative ability of a surface to reflect or emit heat by radiation. Emissivity factors range from 0 to 1; the lower the emissivity, the less heat is emitted through a window system. Emissivity is typically measured by U-factor (or its inverse, R-value).


Enamel: A vitreous substance made of finely powdered glass colored with metallic oxide and suspended in an oily medium for ease of application with a brush. The medium burns away during firing in a low-temperature muffle kiln (about 965-1300°F or 500-700°C).

Sometimes, several rings are required to fuse the different colors of an elaborately enameled object.


Engraving: The production of a design in glass by cutting into the glass surface.

Engraving methods include copper wheel engraving, diamond or tungsten point engraving, acid etching and sand blasting.


EPDM: Ethylene Propylene Diene Monomer – a synthetic rubber.


Etch: To attack the surface of glass with hydrofluoric acid or other agents, generally for marking or decoration.


Evacuated Glazing: An insulating glazing composed of two glass layers, hermetically sealed at the edges, with a hard vacuum between (< 10-3 Pascals) to eliminate convection and conduction. A spacer system (commonly referred to as “pillars”) throughout the surface of glass (rather than just at the edges) is needed to keep the panes from touching.


Expansive Cement: An adhesive used to anchor glass railings into a base.


Extensibility: The ability of a sealant to stretch under tensile load.


Extension Jam: A board or trim component extending from the interior of the window frame to the interior wall. It is used to increase the depth of the jambs of a window to fit a wall of any given thickness.


Exterior Glazed: Glazing infills set from the exterior of the building.


Exterior Stop: The removable glazing bead that holds the glass or panel in place when it is on the exterior side of the light or panel, as contrasted to an interior stop located on the interior side of the glass.


Extrusion: The process of producing aluminum shapes by forcing heated material through an orifice in a die by means of a pressure ram. Also, any item made by this process. An example is the complex cross-section of an extruded aluminum or PVC window frame. A process for the production of continuous strips or rods of material such as glass and also the butyl used in the sealing of insulating glass units. The material, molten in the case of glass, is forced through a die and cut to the required length.


Extrusion Failure: The failure which occurs when a sealant is forced too far out of the joint.




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Facade / Face: The whole exterior side of a building that can be seen at one view; strictly speaking, the principal front. Commonly used as reference to the exterior skin of a building.


Face Glazing: A system having a triangular bead of compound applied with a putty knife, after bedding, setting and clipping the glazing infill in place on a rabbetted sash.


Fanlight: A half-circle window over a door or window with radiating bars.


Fast Cure Urethane: A faster hardening adhesive. The term ‘fast’ is relative to the surrounding temperature and humidity. Curing time is faster than for normal adhesives.


Fastener: An item that attaches one item to another such as a screw, bolt or rivet.


Fatigue Failure: The failure of a material due to rapid cyclic deformation.


Feeder: A mechanism mounted on the casing of the forehearth which delivers the glass in gobs. The rate of flow of the molten glass is regulated by the use of different sized orifices in the feeder spout and by a plunger which pushes the glass through the orifice. Shears for the cutting of the glass flow into gobs are operated through the same cam system as that of the plunger to ensure constant gob size.


Feldspar: Also known as felspar. Any of a group of aluminum silicates of potassium, sodium, or calcium. Used in the batch as a means of adding alumina to the molten glass.


Fenestration: The placement of openings in a building wall, such as windows, doors, skylights, etc., designed to permit the passage of air, light, or people; one of the important aspects of a building’s exterior appearance. Also, associated interior or exterior elements, such as shades or blinds. From the Latin word, fenestra, meaning “window.”


Fiberglass: A composite material made by embedding glass fiber in a polymer matrix. It may be used as a diffusing material in sheet form, or as a standard sash and frame element.

Very fine strands of glass (normally with a high boric oxide and content) used in the form of glass wool for insulation, glass fiber for matting, etc., and also for the reinforcement of plastics.

The principal production process involves blowing jets of steam or air onto molten glass as it emerges from a tank furnace through very small diameter nozzles.


Fillet Bead: Caulking or sealant placed in such a manner that it forms an angle between the materials being caulked.


Film Conductance: The time rate of heat flow from a unit area of a surface to its surroundings, induced by a unit temperature difference between the surface and the environment.


Fining: The process by which gaseous inclusions are removed from the glass melt after all batch materials have been added. Fining agents induce the formation of large bubbles which collect smaller bubbles as they rise to the surface.


Fire Polish: To make glass smooth or glossy by the action of fire or intense heat.


Fire-Protection Rating: The period of time that an opening protective assembly will maintain the ability to confine a fire as determined by tests – NFPA 252/ NFPA 257/UL 9/UL 10c/ASTM E 2010/ASTM E 2074.


Fire Resistance: As applied to buildings, the property of a material or assembly to withstand fire or give protection from it, characterized by the ability to confine a fire or to continue serving a structural function, or both.


Fire-Resistance Rating: The period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both, as determined by tests – NFPA 251/ASTM E 119/UL 263 (wall assemblies).


Fire Windows: Fire endurance-rated glazing material.


Firing: The process of bringing a glass furnace up to its operational temperature and then maintaining the temperature.


Fixed Lite: Non-venting or non-operable window.


Fixed Panel: Non-operable door or panel of glass.


Fixed Window: A single sash fastened permanently in a frame so that it cannot be raised, lowered, or swung open; a non-venting or non-operable window unit.


Flare: A protrusion on the edge of a lite of glass.


Flare-Jaw Pliers: Glass pliers that. Have identical upper and lower jaws, which widen along their length.


Flashing: (1) Sheet metal or other material applied to seal and protect the joints formed by different materials or surfaces. (2) Applying a thin layer of opaque or colored glass to the surface of clear glass, or vice versa.


Flash Point: Minimum temperature at which a liquid gives off a vapor in sufficient concentration to ignite when heated.


Flat Glass: A general term covering sheet glass, plate glass, float glass, window glass, and various forms of rolled glass, and named according to the method used in its manufacture. See also Float glass, Plate glass, Rolled glass, Sheet glass. All types of glass (rolled, float, plate, etc.) produced in a flat form, regardless of the method of production.


Flexing: A method of gaining access to a tight break by flexing the glass back and forth either with a tool or by hand.


Float Glass Process: Glass formed by a process of floating the molten glass (at approximately 1000 degrees Celsius) on a shallow bed of molten tin. Thickness is controlled by the speed at which the solidifying glass ribbon is drawn off the tin bath. The surfaces of the glass do not come into contact with any rollers or mechanisms that could cause damage until the glass has solidified; therefore, it produces a high-optical-quality glass with parallel surfaces without polishing and grinding. A method for the production of high-quality sheet glass whereby a ribbon of molten glass is fed across a bath of heated liquid, usually molten tin, in a carefully controlled atmosphere. The process was developed by the UK firm Pilkington Brothers.


Float Glass: Glass produced by a process in which the ribbon is floated across a bath of molten tin. The vast majority of flat glass is now produced using this method. The terms “plate” glass and “sheet” glass refer to older manufacturing methods still in limited use.


Flowering: A flower-petal effect around the outer edge of a repair. This is caused by the laminate detaching from the outer layer of glass.


Flue: A duct or channel for conveying heat or exhaust gases.


Flush Door: Door produced using two skins or faces separated by a stile-and-rail frame construction at the perimeter. Flush doors may be produced with a hollow core or solid core.


Flush Glazing: A method of glazing wherein the surfaces of the glass retaining members (stops or beads) are in the same plane normal to the glass as the side faces of the frame members; often achieved by providing pockets in these faces.


Flux: A substance that lowers the melting temperature of another substance. For example, a flux is added to the batch in order to facilitate the fusing of the silica. Fluxes are also added to enamels in order to lower their fusion point to below that of the glass body to which they are to be applied. Potash and soda are fluxes.


Foam Glass: Glass with a high bubble content, produced by adding additional gases or gas forming substances to the glass melt. The resulting glass has a very low density but a high compressive strength and dimensional stability, making it particularly suitable for thermally and acoustically insulating construction materials.


Foam Spacer: Nonconductive, foam material (often closed-cell silicone foam) used to separate the double- and triple-pane insulating glass units; improves the thermal performance of the window.


Fogging: A deposit of contamination left on the inside surface of a sealed insulating glass unit due to extremes of temperatures or failed seals.


Forehearth: A refractory tank whose function is to receive glass from the furnace, reduce its temperature to the desired level and discharge it to the feeder mechanism at a uniform temperature. The forehearth usually consists of two sections: a cooling section with burners and cooling ducts which allow the cooling process to be regulated, and a conditioning (equalizing) section generally equipped only with burners which ensure uniform temperature distribution through the glass flow as it enters the feeder.


Founding: The initial phase of melting batch. For many modern glasses, the materials must be heated to a temperature of about 2450°F 1400°C). This is followed by a maturing period, during which the molten glass cools to a working temperature of about 2000°F (1100°C).


Fourcault Process: The method of making sheet glass by drawing vertically upward from a slotted debiteuse block.


Frame: The fixed, enclosing structure of a window or other fenestration system which holds the sash, casement, door panels, etc., as well as hardware. Frames can be constructed from aluminum extrusions, steel, PVC extrusions, wood, composite materials, or a combination of these materials.


Freeze-Thaw Resistance: Resistance to cycles of freezing and thawing that could affect application, appearance, or performance


French Door: Generally refers to a pair of hinged doors that open from the middle. Also incorporates wider stile-and-rail components around the glass than typical glazed doors.


Frit: Ceramic frit opacification is one or more coats of durable colored ceramic material fire-fused onto compatible base glass. The firing also produces a heat-treated product. Since the basic purpose is generally to render the glass opaque, the frit is typically applied to the second surface of monolithic glass or the fourth surface of an insulating unit (counting from the outside surface in). The opacity can be improved with thicker or multiple coats, which are available in a wide range of colors.


Frosted Finish: A surface treatment for glass, consisting of an acid etching of one or both surfaces that diffuses transmitted light and reduces glare.


Frosting: The process of giving a glass surface a matt finish, thus reducing transparency. Frosting may be by means of acid treatment (pouring hydrofluoric acid onto the glass), sandblasting, special glue application and subsequent removal, or mechanical etching with a grinding wheel.


Fully Tempered Glass: Flat or bent glass that has been heat-treated to have either a minimum surface compression of 10,000 psi (69 MPa) or an edge compression not less than 9,700 psi (67 MPa) in accordance with the requirements of ASTM C 1048, kind FT or meet the requirements of ANSI Z97.1 or CPSC 16 CFR 1201. Outside of North America, sometimes called “toughened glass.”


Furnace: An enclosed structure for the production and application of heat. In glassmaking, furnaces are used for melting the batch, maintaining pots of glass in a molted state, and reheating partly formed objects at the glory hole.


Furnace, Pot: A pot furnace consists of a melting chamber lined with refractory brick, a vaulted roof or “crown” of silica brick, and external walls made of insulating brick. Below the upper chamber in which there may be as many as twelve melting pots, there is a lower section for the pre-heating of the fuel gas. Pot furnaces are used today in the manufacture of mouth-blown glass objects and special glasses.


Furnace, Tank: See Tank


Fusing: (1) The process of founding or melting the batch; (2) heating pieces of glass in a kiln or furnace until they bond (see casting and kiln forming); (3) heating enameled glasses until the enamel bonds with the surface of the object.


Fusing Glass-to-Glass: Glasses of different compositions can be fused together for decorative purposes and also in the sealing of electrical, medical and industrial components. The fusion temperature for soda-lime glasses is generally between 760°C and 820°C. Particular attention must be paid to the thermal expansion coefficients of different glass types.


Fusion-Weld: A term for a type of corner construction, used with vinyl and other types of windows and doors, in which a small amount of material on the ends of two pieces are melted or softened, then pushed together to form a single piece. This also is referred to simply as a welded corner.




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Garnish Moldings: The interior decorative moldings around the perimeter of glass parts.


Gasochromic Glazing: Glazing which uses the phenomenon of chromism due to tin injection/ejection to color the window. The application of gas flow transporting ions to the surface (catalyst), which changes solar and visible transmittance.


Gas Fill / Gas Filled IGU: A gas, usually argon or krypton, placed between window or skylight glazing panes to reduce the U factor by suppressing conduction and convection.


Gasket: A pre-formed section, generally of neoprene or rubber-like composition, that provides a continuous sealing for the glass or frame members. It provides a weather tight seal when compressed.


Gas Retention: The ability of a sealed insulating glazing unit to retain its original gas filled composition. In the long term, diffusion through frame and edge seal materials allows air to progressively replace the original gas(es).


G Factor: Same as Solar Heat Gain Coefficient (SHGC). This quantity is related to Total Solar Energy Transmittance (TSET). In some countries, it is formally applied to only the glazing, but generally applies to both transparent and opaque parts of a fenestration system.


Girth: In bent glass, the distance around the concave or convex surface measured perpendicular to the height, including any flats.


Glare: High luminosity values from a point, line, or area source that may affect the visual amenity, depending on luminosity, background illumination, adaptation of the eye, and area size. There are upper limits for physiological glare (damage to the eyes) and psychological glare (feeling of discomfort).


Glare Veiling: Diffuse scattering from a glazing system, which obscures (masks) the visibility of objects beyond the glazing system.


Glass: An inorganic, hard, brittle substance, usually transparent, that is made by fusing silicates (sand), soda (sodium carbonate), and lime (calcium carbonate) with small quantities of alumina, boric, or magnesia oxides under high temperatures, without crystallizing. Contrary to common belief, glass is not solid, but is rather a very hard fluid which flows slowly. A homogeneous material with a random, liquidlike (non-crystalline) molecular structure. The manufacturing process requires that the raw materials be heated to a temperature sufficient to produce a completely used melt, which, when cooled rapidly, becomes rigid without crystallizing.


Glass Ceramics: Materials produced from glass which have a polycrystalline structure. Most offer advantages of low thermal expansion, making them suitable for uses such as cookware. Others have high physical strength and can be machined like metals.


Glass Clad Polycarbonate: One or more lites of flat glass bonded with an aliphatic urethane interlayer to one or more sheets of extruded polycarbonate in a pressure/temperature/vacuum laminating process.


Glass Fines: Minute glass particles typically resulting from glass fabrication processes (i.e. cutting, grinding, polishing, drilling, edging, etc)


Glass Quality (Flat): Defined by ASTM C 1036 on the basis of end use and allowable blemishes.


Glazing: A generic term used to describe an infill material, such as glass or window assemblies in general. Also refers to the process of applying or installing glass into a window or door sash.


Glazing Bar: See Muntin


Glazing Bead: A small applied molding used to hold a pane of glass, or substitute for it, in a frame.


Glazing Channel: A three sided U shaped sash detail into which a glass product is installed and retained.


Glazing Compounds: A soft dough-like material used for filling and sealing the space between a pane of glass and its surrounding frame.


Glazing Stop: A component of the sash or door panel that holds the glass in place.


Glider: A window with a movable sash that slides horizontally. Also referred to as a Horizontal Sliding Window.


Glory Hole: A hole in the side of a glass furnace, used to reheat glass that is being fashioned or decorated. The glory hole is also used to fire polish cast glass to remove imperfections remaining from the mold.


Gob: A drop of still molten glass formed by the cutting of the stream of glass as it flows from the forehearth through a feeder into a spout/orifice of variable diameter; the greater the diameter, the larger the gob. The gobs are fed into the forming machine to be molded into bottles and other glass objects.


Gob Feeder: A machine mounted at the end of the forehearth that dispenses gobs of molten glass of consistent size and weight for forming into glass containers. From the spout of the forehearth the molten glass flow out through an orifice, the size of which influences the flow rate of the glass. A cylindrical plunger moves up and down to accelerate or slow the flow of molten glass through the orifice. Linked to the motion of the plunger is a shear that cuts the molten glass into gobs at the correct point in relation to the plunger action. The gobs are then fed down chutes to the forming machine.


Green Building: A movement in architectural and building circles aimed at creating structures that are occupant and environmentally friendly. Criteria such as sustainability, energy efficiency and healthfulness are considered.


Green Strength: A term used by some adhesive manufacturers to describe initial strength of an adhesive.


Grille: A term referring to window pane dividers or muntins. It may be a type of assembly fitted to the interior of the window or door unit that can be detached for cleaning. Also can be fitted inside the sealed insulating glass unit, when it also is referred to as a grid.


Grinding: The removal of glass with abrasives or abrasive (grinding) wheels in order to shape, polish or otherwise finish both flat and hollow glass. Grinding processes include milling, sawing, edging and drilling.


Grit: The amount of tiny abrasive material contained within a given area of an abrasive material.


Grommet: A ring or eyelet. In electricity, an insulated washer of rubber or plastic inserted in a hole in a metal part to prevent grounding of a wire passing through the hole.


Gun Grade / Gunnable Sealant: Sealant that is meant to be applied with a caulking gun.


Gun Consistency: Sealant formulated in a degree of viscosity suitable for application through the nozzle of a caulking gun.


Ground Glass: A light-diffusing glass, usually sandblasted or ground.




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Hard Coat(ing): A low-emittance (low-E), thin-film surface coating on sheet glass which is deposited at a high temperature during the final stage of glass production. It is resistant to abrasion and attack by moisture, atmospheric pollutants, etc.


Haze: The scattering of visible light, resulting in a decrease in the transparency of a window system and a cloudy appearance.


Hazardous Materials: Materials deemed to be of danger or risk to humans, animals or the environment.


HAZCOM: Hazardous Communications is a document required by OSHA that contains a company’s policies and procedures as well as procedures for handling and disposing of hazardous materials.


HAZMAT: Is an abbreviation for hazardous materials – substances in quantities or forms that may pose a reasonable risk to health, property, or the environment. HAZMATs include such substances as toxic chemicals, fuels, nuclear waste products, and biological, chemical, and radiological agents.


Head: The main horizontal member forming the top of a window or door frame.


Header: Horizontal framing member placed over the top of a window or door.


Heat Absorbing Glass: Glass having the property of absorbing a substantial percentage of radiant energy in the near-infrared range of the spectrum.


Heat Flow Rate (Q): The quantity of heat transferred to or from a system in unit time.


Heat Gain: Instantaneous rate of heat gain at which heat enters into and/or is generated within a space. Latent heat gain occurs when moisture is added to the space from occupants or equipment. Sensible heat gain is added directly to the space by conduction, convection, and/or radiation.


Heating Degree Day: Term used to relate the typical climate conditions to the amount of energy needed to heat a building. The base temperature is usually 65 degrees fahrenheit. A heating degree day is counted for each degree below 65 degrees that the average daily outside temperatures reach in the winter.


Heat Loss: The transfer of heat from inside to outside by means of conduction, convection, and radiation through all surfaces of a building.


Heat Loss Rate: The rate at which heat is lost from a system or component of a system, per degree of temperature difference between its average temperature and the average ambient air temperature.


Heat Mirror™: A thin, transparent-coated (low-e) polymer film that is inserted between double or triple glazing, which permits transmission of visible light but reflects far-infrared (and sometimes near-infrared) radiation. Heat Mirror is a commercial trademark of Southwall Technologies for their proprietary soft-coated, low-e polyester glazing films.


Heat Resistant Glass: Glass which has a low coefficient of expansion and which is therefore less liable to thermal shock. Borosilicate glass is the most common type of heat resistant glass.


Heat Strengthened Glass: Glass that has been subjected to a thermal treatment characterized by rapid cooling to produce a compressively stressed surface layer somewhat less stressed than that produced in tempered glass. Heat-strengthened glass is approximately twice as strong as annealed glass of the same thickness when exposed to uniform static pressure loads. Heat-strengthened glass is not considered safety glass and will not completely dice as with fully tempered glass. Flat or bent glass that has been heat-treated to have a surface compression between 3,500 and 7,500 psi (24 to 52 MPa) and meet the requirements of ASTM C 1048, kind HS. Heat strengthened glass is not a safety glazing material and will not meet the requirements of ANSI Z97.1 or CPSC 16 CFR 1201.


Heat Treated Glass: A term sometimes used for both fully tempered and heat strengthened glass.


Heated Urethane: A type of adhesive that is heated to a prescribed temperature before application. The heat pre-cures the adhesive for faster setting.


Heating Up: Raising the temperature within the furnace to the required operating temperature under strictly controlled conditions, ensuring the homogenous expansion of refractory materials.


Heel Bead: Sealant applied at the base of a channel, after setting the lite or panel and before the removable stop is installed; one of its purposes being to prevent leakage past the stop.


Heliostat: A sun tracking device. Typically, an instrument consisting of a mirror or other reflective surface moved by clockwork, by which a sunbeam is made apparently stationary, by being steadily directed to one spot during the whole of its diurnal period. A heliostat, for instance, might be used with a skylight, reflecting direct sunlight through the aperture throughout the day to increasing illuminance.


High Transmission Glass: Glass that transmits an exceptionally high percentage of visible light.


Holographic Glazing: Glazing with a thin-film microstructure coating that refracts incident light in some advantageous way, e.g. as a light redirecting glazing for daylighting applications.


Hollow Ware: Made generally of soda-lime glass, but also of crystal, lead crystal and special glasses, hollow ware includes a wide variety of containers and receptacles: container glass (bottles, jars, medical and packaging glass), tableware (drinking glasses, bowls, etc), construction hollow ware (glass building blocks, etc), medico-technical glassware (laboratory equipment, tubing, etc) and lighting glass (lamps, bulbs, etc).


Hopper Window: A partially movable sash that is hinged at the bottom and opens inward.


Hone Angle: An important characteristic of a cutting wheel that determines the sharpness of the wheel.


Horizontal Pivoted Window: A window fitted with a ventilator; it opens by rotating on centrally located pivots on upright frame members.


Horizontal Sliding Window / Horizontal Slider: A window fitted with one or more sashes that opens by sliding horizontally in grooves provided in horizontal frame members. An operating sash with a fixed light (comprising a unit) is termed a single slider.


Horizontal Tempering: The tempering process where the glass travels through the oven in horizontal plain.


Hot Melt Butyl: An insulating glass edge sealant used during manufacturing.


Humidity, Absolute: The mass of water vapor per unit of volume.


Humidity, Relative: The percentage of moisture in the air in relation to the amount of moisture the air could hold at that given temperature.


Hot Spot: Inside the furnace, the hot spot is that area on the surface of the melt which has reached the maximum temperature (at which batch reactions have been completed and dissolved gases have been reduced to acceptable levels).




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IG Units: Common name for insulated glass units.


I.S. Machine: I.S. (Independent/Individual Section) container forming machines are made up of individual but identical sections placed side by side in line. Each section comprises an arrangement of mechanisms with gears enabling the sections to be started or stopped independently of the others, making the I.S. machine more flexible than continuous or intermittent motion rotary machines.


Impact Resistance: The ability to withstand mechanical blows or shock without damage seriously affecting the effectiveness of the material or system. Term used to describe window and door products that have passed established tests for resistance to windborne debris. Such products are typically used in coastal areas that are prone to hurricanes.


Inert Gas: Refers to the use of chemically nonreactive gas(es) within the cavity of a sealed insulating glass unit for the purpose of reducing conductive/convective heat transfer.


Infiltration Air: The movement of outdoor air into the interior of a building through cracks around windows, doors, and the building envelope in general.


Infiltration Heat Loss: The heat loss due to infiltration. The loss depends upon the indoor and outdoor temperatures, the crack perimeter, and the rate of air leakage per foot of crack.


Infrared: Part of the light spectrum; infrared rays that cause heat.


Insulating Glass (IG): Two or more lites of glass with a hermetically sealed airspace between the lites. The sealed space may contain air or be filled with an inert gas, such as argon.


Infrared Lamp: An incandescent lamp working at a low filament temperature and consequently emitting relatively high amounts of infrared radiation. Infrared bulbs are usually made of borosilicate glass with molybdenum or tungsten wires.


Infrared Radiation (IR): Invisible electromagnetic radiation, beyond red light on the spectrum, with wavelengths greater than 0.7 microns. Short-wave infrared radiation is from 770 nm to 2500 nm (0.77 to 2.5 microns), while long-wave infrared is from 2.5 microns and beyond.


Inleakage: The unwanted entry of air into a furnace through expansion created gaps in the furnace superstructure or through other areas such as burner ports, regenerators and exhaust flues. Inleakage can result in decreased efficiency and increased fuel costs.


Insulating Glass (IG) / Insulating Glass Unit (IGU): A combination of two or more panes of glass with a hermetically sealed air space between the panes of glass, separated by a spacer. This space may or may not be filled with an inert gas, such as argon.


Integrated Sash: A sash unit in which the insulating glass spacer profiles are integrated into the sash profiles. Separate IG construction is eliminated as the two lites of glass are applied and sealed directly to the sash, creating one assembly.


Interior Glazed: Glazing infills set from the interior of the building.


Interior Stop: The removable molding or bead that holds the lite in place when it is on the interior side of the lite.


Interlayer: Any material used to bond two lites of glass and/or plastic together to form a laminate.


Interior Venetian Blinds: A venetian blind installed between two panes of glass and remotely controlled.




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Jal Awning Window: A window consisting of multiple top hinged ventilators arranged in a vertical series and operated by one or more control devices that swing the bottom edges of the ventilator outward. The window does not contain a cross shaft or torque bar, but does have an individually operated locking mechanism.


Jalousie Window: Window made up of horizontally mounted, louvered glass slats that tightly abut each other when closed and rotate outward when cranked open.


Jamb: The main vertical members forming the sides of a window or door frame.


Jamb Depth: Width of a window or door from the interior to the exterior of the frame.


Jambliner: The track installed inside the jambs of a double hung window, on which the window sash slide.


J Channel: Installed or built-in to the side of a window or door, this channel is designed to accommodate the ends of siding pieces to provide a finished appearance.


Joint Design: The design of a void to be filled with sealants to prevent air or water leakage.


Joint: The opening between component parts.




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Kiln: An oven used to process a substance by burning, drying or heating. In contemporary glass working kilns are used to fuse enamel and for kiln forming processes such as slumping.


Kiln Forming: The process of fusing or shaping glass usually in or over a mold by heating it in a kiln.


Kink: An abrupt deviation from a flat plane or the normal contours of bow and warp, and most commonly found near the edge of a piece of heat treated glass.


Knife Consistency: Compound formulated in a degree of firmness suitable for application with a putty knife such as used for face glazing and other sealant applications.


Knocked Down (KD): Fabricated framing components shipped loose for assembly at another location.


Krypton: An inert, nontoxic gas used in insulating windows to reduce heat transfer.


kWh: Kilowatt-hour; a unit of energy equal to one thousand watt-hours.




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L Squares: An ‘L’ shaped instrument that can be made of wood, plastic, aluminum, or phenolic resin, and has two edges perpendicular to each other, used as a guide for the glass cutter when making 90° angle cuts to the edge of a sheet of glass.


Lacing Tool: Tool whose eyelet threads the locking strip while its heel presses the locking strip into the channel.


Laminate: Vinyl inner layer of laminated glass.


Laminated Glass: Two or more sheets of glass bonded together with one or more inner layers of transparent plastic (interlayer) to which the glass adheres if broken. The bonding is achieved by heating the glass/interlayer sandwich under pressure in an autoclave. The glass is used for overhead, safety glazing and sound reduction. Laminated or compound glass consists of two or more sheets of glass with one or more viscous plastic layers sandwiched between the glass panes. The solid joining of the glasses takes place in a pressurized vessel called an autoclave. In the autoclave, under simultaneous heating of the already processed layers of glass and special plastic, lamination occurs. When laminated safety glass breaks, the pieces remain attached to the internal plastic layer and the glass remains transparent.


Laminated Plastics / Plastic Laminates: Two or more lites (or sheets) of polycarbonate (or acrylic) with an aliphatic urethane interlayer between polycarbonate or acrylic bonded together under heat and pressure.


Lap Joint: A joint in which the component parts overlap so that the sealant or adhesive is placed into shear action.


Lap Shear Strength: The strength demonstrated by the diagonal pull of two substrates until adhesive failure. The name comes from the lap joint created by the test samples and the shear action used to pull the samples apart.


Lathes: Two distinct types of lathe exist although both basically consist of a horizontal shaft rotated by a motor. The first type uses the shaft to spin an abrasive wheel (often at high speed) in order to cut, score or polish glass; the second type uses the shaft to rotate a piece of glass so that it can be heated and manipulated.


LCD Switchable: Form of chromogenic (switchable) glazing that employs a liquid crystal device to modulate transmittance of solar radiation.


Lead Crystal: The type of glass produced when lime in the batch is replaced by lead oxide. The composition of lead crystal is 54-65% silicon dioxide (SiO2), 18-38% lead oxide (PbO), 13-15% soda (Na2O) or potash (K2O), and other oxides. Such glass has a high refractive index and is particularly suited for decoration by cutting.


Lehr: A special type of oven or kiln used specifically for annealing glass. In industrial production, it usually has a moving belt to carry the glass through at controlled speeds and is divided into different areas each with its own heat source, making it possible to carefully regulate the temperature gradient to which the glass is submitted. In smaller workshops, the lehr may be a simple kiln with a shelf for the glassware rather than a moving belt, and with electronic controls to program the temperature cycle required.


Libbey-Owens Process: A method for the production of sheet glass by means of a continuous drawing process. Devised by the American Irving Colburn and further developed with the support of the US glassmaker Libbey-Owens, the process was patented in 1905 and was first used for commercial production in 1917. The glass ribbon is drawn vertically from the tank for about 70 cm by a metal bait before being bent over a roller into the horizontal plane ready for cutting and annealing. The drawing speed with the Libbey-Owens process is twice that of the Emile Fourcault process.


Light / Lite: A window; or a pane of glass within a window. Double hung windows are designated by the number of lights in the upper and lower sashes, as in six-over-six.


Light Scoops: Clerestory roof monitors oriented away from the sun, utilized when and where indirect light is desired or solar heat gains are undesirable.


Light Pipe: A generic term for a system employing bulk optics (lenses, mirrors, reflective ducts or other optical waveguide technology) designed to transport light (natural or artificial) to parts of a building remote from the envelope. Also known as Tubular Daylighting Devices (TDD).


Light Redirection System: A glazing unit or panel, possibly retrofitted, which intercepts incident sunlight and sky light and reflects it in another direction, usually toward the ceiling.


Light Shaft: An insulated shaft built to direct the light from a roof window or skylight through the attic to the room below.


Light Shelf: A daylight enhancement device; an internal and/or external overhang with a reflecting upper surface normally above head height. Designed to reduce glare near the window and improve illuminance uniformity along an axis normal to the window wall.


Light-to-Solar-Gain Ratio (LSG): A measure of the ability of a glazing to provide light without excessive solar heat gain. It is the ratio between the visible transmittance of a glazing and its solar heat gain coefficient.


Light Transmittance: The percentage of visible light able to pass through.


Lightwell: An open shaft in a building that provides air and light to windows opening onto the shaft.


Limestone: A sedimentary rock composed mainly of calcium carbonate which is added to the batch to provide calcium oxide.


Lintel / Header: A structural component or beam above a window or door opening that supports the wall above.


Liquid Crystal Glazing: Glass in which the optical properties of a thin layer of liquid crystals are controlled by an electric current, changing from a clear state to a diffusing state.


Lite: A term for a pane or finished piece of glass. In windows and doors, refers to separately framed panes off glass as well as designs simulating the look of separately framed pieces of glass.


Litrium / Literium: An atrium designed to optimize daylighting in adjacent spaces.


Live Load: Loads produced by the use and occupancy of the building or other structure and do not include construction or environmental loads such as wind load, snow load, ice load, rain load, seismic load or dead load.


Load: The amount of energy that must be added to or extracted from a space to thermal comfort. Sensible or latent cooling or heating loads are due to accumulated heat gains or losses through the building envelope, window, infiltration or ventilation and occupancy.


Long Wave Infrared Radiation: Invisible radiation, beyond red light on the electromagnetic spectrum (above 2.5 micro meters or microns), emitted by warm surfaces such as a body at room temperature radiating to a cold window surface.


Louvered Window: A window having louvers or slats that fill all or part of the opening.


Louvers: Slanted fins or slats in a window, ventilator or venetian blind; the slats may be fixed or adjustable and made of wood, metal, glass or plastic.


Low Conductance Spacers: An assembly of materials designed to reduce heat transfer at the edge of an insulating window. Spacers are placed between the panes of glass in a double or triple glazed window.


Low-E / Low-Emittance Coating: A microscopically thin (less than 100 nm) metal, metal oxide, or multilayer coating deposited on a glazing surface to reduce its thermal infrared emittance and radiative heat transfer. Near-infrared emittance may also be reduced depending on whether solar heat is to be rejected or admitted. Low-emissivity glass is used to increase a windows insulating value, block heat flow and reduce fading.


Low Emissivity on Low-E Glass: Commonly known as low-E glass and often used in double and triple glazing units, this window glass has a special thin-film metallic or oxide coating which allows the passage of short-wave solar energy into a building but prevents long-wave energy produced by heating systems and lighting from escaping outside. Low-E glass thus allows light to enter while also providing thermal insulation.


Low Iron Glass: Glass with a low concentration of ferrous compounds, which are absorbing in the near-infrared part of the solar spectrum. Particularly used for solar collector covers and equator facing windows in cold climate, passive solar buildings where solar transmittance must be maximized.


Luminous Efficacy (Light-to-Solar Gain Ratio): The ratio of the visible transmittance to the shading coefficient; it is a measure of the light-to-heat ratio of the transmitted energy.




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Masonry Opening: Area in a masonry wall left open for windows or doors.


Mastic (broad interpretation): Any field molded sealant or adhesive. Includes materials which are gunned, poured or troweled into place.


Material Safety Data Sheets (MSDS): Required for all toxic or hazardous materials used by a company. The sheets have information on the chemicals as well as what to do when exposed to the materials.


Mechanical Window: A term for a product, usually vinyl, in which the corners are assembled using screws or other fastening mechanisms, as opposed to a welded corner construction.


Medium-Density Fiberboard (MDF): A wood fiber composite used in a variety of window, door and millwork applications.


Melt: The fluid glass produced by melting a batch of raw materials.


Metal Clad Window: Exterior wood parts covered with extruded aluminum or other metal with a factory applied finish for protection.


Metal Window: A window composed of a metal frame and sash; the metals can be aluminum, steel, stainless steel and bronze however, the vast majority of metal frames are made of aluminum.


Micron: One millionth (10-6) of a metric meter.


Microscopic Surface Particles: Any glass fines, debris, dust, grit, refractory particles, etc that are invisible to the naked eye and adhere to one or both glass surfaces during the heat treating process.


Migration: Spreading or creeping of a constituent of a compound onto/into adjacent surfaces.


Mil: One thousandth of an inch, or 0.0254 millimeters.


Mirrors: Polished glass with a reflective coating of silver deposited on the back.


Misco: Wire glass where the wire is a diamond pattern.


Mixed Feed: The transfer of the various ingredients of the batch into the mixer by means of hoists, buckets and conveyor systems.


Mobile Unit: A vehicle, usually a van or light truck, properly equipped with glass, mirrors, safety equipment and tools and driven to a glass repair customer home or place of business.


Model Building Code: A resource of codes that have been written and adopted as the law or standard in a geographical area.


Modulus: The ratio of stress to strain.


Moisture Migration: The passage of moisture into or through a material or construction, in the form of water vapor, due to a difference in vapor pressure at the two faces.


Molded Glass: Glass that is formed in a mold, as distinct from cast, rolled, drawn or offhand ware.


Molding or Chrome Release Tool: Tool used to remove molding clips from a frame or back lite.


Monitor: A raised section of roof that includes a vertical, or nearly vertical, glazed aperture for daylighting.


Monomer: A material composed of single molecules. A building block in the manufacture of polymers.


Mortise Lock: A lock fitting a rectangular shaped cavity in the edge of a door.


Mold: A form, normally made of wood or metal, used for shaping and/or decorating molten glass. Some molds (e.g., dip molds impart a pattern to the parison, which is then withdrawn, blown and tooled to the desired shape and size; other molds are used to give the object its final form, with or without decoration.


Mold, Block: A particular type of mold produced in a single piece of cast iron, hollowed into a specific shape using a cold deformation process. Used in the production of pressed glass hollow ware.


Mold, Dip: A cylindrical, one-piece mold open at the top so the gather can be dipped into it and then inflated.


Mold, Optic: An open mold with a patterned interior in which a parison of glass is inserted, then inflated to decorate the surface.


Muffle Kiln: A low temperature kiln for refiring glass to fuse enamel, fix gilding and produce luster.


Mullion: A major structural vertical or horizontal member connecting windows, sliding glass doors or frames.


Muntin / Muntin Bars / Muntin Grilles: Small, secondary horizontal or vertical framing members that divide glazing into separate vision areas within the basic framework of a door, window, sash or ventilator. Sometimes referred to as sash bar, window bar, or glazing bar.




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Nailing Fin: An accessory component or integral extension of a window or patio door frame that generally overlaps the conventional stud construction and through which nails are driven to secure the frame in place.


Narrow Neck Ware: Glass containers, such as bottles, whose opening is tapered and of smaller diameter than the body of the vessel.


Natural Convection: A heat transfer process involving motion in a fluid (such as air) that is caused by a difference in the density of the fluid and the action of gravity. This is an important part of heat transfer from the glass surface to room air.


Natural Ventilation: Air movement into and out of a building due to wind or differences in air pressure or temperature.


Neck Ring: In the production of glass containers, the tool coupled with the blank mold (parison) which gives the shape to the neck of the container. During the shaping process in the IS machine, the neck ring transports the glass container into the blow mold or finishing mold.


Negligent: Habitually guilty of neglect, extremely careless or casual.


Neoprene: A synthetic rubber having physical properties closely resembling those of natural rubber but not requiring sulfur for vulcanization.  Extremely good weather resistance (both heat and cold) with ultraviolet stability.


Non-Drying / Non-Curing: A sealant that does not set up or cure.


Non-Sag: A sealant formulation having a consistency that will permit application in vertical joints without appreciable sagging or slumping. A performance characteristic, which allows the sealant to be installed in a sloped or vertical joint application without appreciable sagging or slumping.


Non-Skinning: Descriptive of a product that does not form a surface skin.


Non-Staining: Characteristic of a compound which will not stain a surface.


Nozzle: The tubular tip of a caulking gun through which the compound is extruded.




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Obscure Glass: Any textured glass (frosted, etched, fluted, ground, etc.) used for privacy, light diffusion or decorative effects. Also known as vision proof glass.


Obsidian: Glass made by natural forces, often found in volcanic areas where heat has acted upon sand, sodium and calcium compounds to produce glass.


OEM: Abbreviation for Original Equipment Manufacturer.


Off Set Pliers: Pliers used to trim glass in hard to reach places. The jaws contact the glass at right angles to its edge.


One Part Sealants: Sealants requiring no premixing.


One Part Urethane: An adhesive used in glass replacement that has only one component.


One Step Distributor: An industry term for a wholesale company which buys building products from a manufacturer and sells them to builders, contractors and homeowners is referred to as a one-step distributor. A wholesaler that buys building products from the manufacturer and sells them to lumberyards and home centers, which in turn sell to builders, contractors and homeowners is referred to as a two-step distributor.


Opacifier: A material, either film or liquid, that is applied to the back of a piece of glass to act as a light shield.


Opalescent: Name of the texture of a type of art glass.


Opaque: Impenetrable by light.


Open Time: The time interval between the application of an adhesive and when it becomes no longer workable.


Open Celled: As in open-celled foam. Foam extrusions can have the body contain connecting open cells. This allows air to pass through the foam to promote adhesive cure.


Operable Window: A window that can be opened for ventilation.


Optical Glass: High quality glass with closely specified optical properties; It is used in the manufacture of optical systems.


Oriel: Type of bay window which protrudes from building, but does not touch the ground.


Organic: Any compound which consists of carbon and hydrogen with a restricted number of other elements, such as oxygen, nitrogen, sulphur, phosphorous, chlorine, etc.


Outdoor-Indoor Transmission Class (OITC): A single number rating calculated in accordance with ASTM E 1332, using values of outdoor-indoor transmission loss. It provides an estimate of the sound insulation performance of a facade or building elements. The frequency range used is typical of outdoor traffic noises.


Outside-Inside Transmission Class (OITC): A rating used to classify the performance of glazing in exterior applications.


Oval Cutter: Cutters that allow glaziers to cut ovals of specific dimensions. Oval cutters can also cut circles.


Owens-Illinois Coating Techniques: Techniques developed by the Owens Illinois company for the surface treatment of glass containers. The two main types are stearate and polyethylene based.

Stearate treatment using polyoxyethylene monostearate gives good lubricity and reduced friction. It is water soluble and not water repellent, facilitating the application of labels. Stearic acid is of vegetable origin, making this type of coating also suitable for kosher foods. However, since the stearate is destroyed by firing or any subsequent processing, the treatment needs to be repeated after the firing of applied color labels. Polyethylene coatings are deposited from a water emulsion but are not water soluble and can thus withstand washing and pasteurizing. Although they are slightly water repellent, most glues used ensure satisfactory adhesion. Polyethylene coatings are transparent and give high luster and lubricity to the glass surface.


Oxidation: Formation of an oxide; the deterioration of rubbery materials due to the action of oxygen or ozone.


Ozone: A reactive form of oxygen. A powerful oxidizing agent occuring naturally in the atmosphere.




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Palladian: A large arch-top window flanked by smaller windows on each side.


Pane: One of the compartments of a door or window consisting of a single sheet of glass in a frame; also, a sheet of glass, or a substitute for it, cut to size and shape and ready for glazing. Often called a square or a light.


Panel: Component mounted within stile-and-rail members of doors; used to refer to the entire door.


Panning: In replacement window work, the outside aluminum trim that can extend around the perimeter of the window opening; it is used to cover up the old window material. Panning can be installed in the opening or attached directly to the window before installation.


Particle Dispersed Glazing: Glazing in which the orientation of small particles between two sheets of glass is controlled electrically, thus changing its optical properties.


Parting Stop: A narrow molding, either integral or applied, that holds a sash or panel in position in a frame.


Passive Solar Heat Gain: The direct admittance of solar heat to a building (usually deliberately and in winter) through windows to reduce or eliminate the need for additional heating energy.


Passive System: A solar heating or cooling system that uses no external mechanical power to move the collected solar heat.


Pattern Cutters:  Patterned glass is one type of rolled glass having a pattern impressed on one or both sides. Used extensively for light control and decorative glazing. Sometimes called rolled or rough rolled glass.


Patterned Glass: One or both surfaces of glass with a rolled design; it is used for privacy and light diffusion.


Peak Demand: The maximum hourly total building electricity use in the year. Electricity uses include space conditioning equipment such as chillers, fan coil units, electrical reheat coils, auxiliary equipment such as pumps and fans, electric lighting, and other office equipment (computers, copy machines, etc).


Peak Load: The maximum hourly total building heating or cooling load in the year.


Peel Test: A test of an adhesive or sealant using one rigid and one flexible substrate. The flexible material is folded back (usually 180°) and the substrates are peeled apart. Strength is measured in pounds per inch of width.


Pellet: A small block of compressed matter. Pre-weighed and mixed batch materials are available in the form of pellets.


Pelletizing: The preparation of materials, e.g. batch ingredients, in pellet form.


Performance (energy): The thermal, solar, and visual properties of a product influence the building energy balance due to solar gains, heat loss, and daylight, and require auxiliary energy from artificial lighting, heating, and cooling; ventilation energy (fans) may also be affected. Therefore, a product has an impact on the overall primary energy use in a building.


Performance Class: There are five window performance classes; R – Residential, LC – Light Commercial, C – Commercial, HC – Heavy Commercial, and AW – Architectural. This classification system provides for several levels of performance so the purchaser or specifier may select the appropriate level of performance depending on climatic conditions, height of installation, type of building, etc.


Performance Grade / Design Pressure: The minimum level of design pressure (air, water, wind) a product must be tested at to achieve a particular rating.


Perimeter Heating: A system of heating in which radiators or registers are located along the exposed wall, usually below windows; heated air from the heating devices counteracts the cold convection flow from the windows.


Perm: Empirical unit of water-vapor permeance (mass flow rate), equal to one grain (avoirdupois) of water vapor per hour flowing through one square foot of material or construction induced by a vapor-pressure difference of one inch of mercury between the two surfaces.


Permanent Set: Occurs when a sealant is stretched, released, and does not return to its original length, but remains longer.


Permeability: The ability of a porous material to permit transmission of water vapor.


Permeance: A measure of the transmission of water vapor through a material expressed in units of perms.


Personal Protective Equipment (PPE): The safety gear worn by persons engaged in work with safety concerns and includes nitrile gloves, safety or ultraviolet glasses, dust and mist masks, first aid kits, and any additional equipment required by company policy and OSHA.


Phial: See Vial


Philips Process: A variation of the Schuller up-draw process patented in Germany in 1931 for the mechanical manufacture of glass tubing and rod.


Photochromic Glazing / Photochromics: Glazing which changes its thermal, solar, and visible transmittance in response to outdoor illuminance or ultraviolet (UV) radiation.


Photopic Response Function: See V-lambda curve.


Photovoltaic: A device that produces electricity (voltage) directly from sunlight (photons).


Picture Window: Large, non-operating window. It is usually longer than it is wide to provide a panoramic view.


Pigment: A coloring substance or matter.


Pivot / Pivoted Window: A window with a sash that swings open or shut by revolving on pivots at either side of the sash, or at the top and bottom.


Plastic Film: A thin, plastic substrate sometimes used as the inner layers in a triple or quadruple glazed window.


Plasticizer: A material which softens a sealant or adhesive by solvent action.


Plate Glass: Flat glass with surfaces that are essentially plane and parallel; it is formed by a rolling process, ground, and polished on both sides. It is available in thicknesses varying from 1/8″ to 1-1/4″ (3.2 mm to 31.8 mm), but has been replaced by float glass. Flat glass made by the casting or rolling of molten glass which is then mechanically ground and polished to produce a smooth and transparent sheet.


Plunger: A tool used in the production of glass containers during the first stage of shape forming in the IS machine. The task of the plunger is to help give the glass container its final shape inside the parison (or blank mold).


Pocket / Channel: A three sided, U-shaped opening in a sash or frame to receive glazing infill. Contrasted to a rabbet, which is a two-sided, L-shaped section, as with face glazed window sash.


Pocket / Channel Depth: The inside dimension from the bottom of the pocket to the top. Pocket depth equals the bite plus the edge clearance.


Pocket Glazing: See Flush Glazing


Pocket Window: A unit designed for replacement applications; is installed into the existing window frame after removal of the sash, balance hardware and parting stops. Also called an insert window, these units allow existing interior and exterior trim to be maintained.


Pocket (Channel) Width: The measurement between stationary stops (or stationary stop and removable stop) in a U-shaped channel.


Points: Thin, flat, triangular or diamond shaped pieces of zinc used to hold glass in wood sash by driving them into the wood.


Point Fixings: In contrast to mullions or patch fittings, which project beyond the plane of the glazing, point fixings are interior. Typically, holes are drilled into the glass and bolts or screws attach the glass in an interior frame structure.


Polariscope: A device for examining the degree of strain in a sample of glass.


Polished Wire Glass: Wire glass that is ground and polished on both sides.


Polishing Lubricant: A lubricant use to aid in polishing glass and plastics.


Polycarbonate: A plastic material used for glazing.


Poly-Isobutylene Tape / PIB Tape: Used to form the primary seal of a dual seal insulating glass unit.


Polymer: A compound consisting of long chain-like molecules. The building units in the chain are monomers.


Polysulfide Rubber: A synthetic polymer usually obtained from sodium polysulfide. Polysulfide rubbers make very good sealants.


Polysulfide Sealants: Sealants that adhere well to glass, aluminum and spacer and corner materials.


Polysulfide: An adhesive used to bond glass to materials prior to the advent of urethane.


Polyvinyl Butyral (PVB): Plastic material used as the interlayer in the construction of some types of laminated glass.


Polyvinyl Chloride (PVC): Polymer formed by polymerization of vinyl chloride monomer.


Pot: A fire clay container placed in the furnace in which the batch of glass ingredients is fused and kept molten. The glass worker gathers directly from the pot.


Pot Life: The time interval following the addition of an accelerator before a chemically curing material will become too viscous to apply satisfactorily.


Preformed Gaskets: Glazing gaskets manufactured to window openings, usually made of rubber or urethane.


Preformed Sealant: A sealant which is pre-shaped by the manufacturer.


Pre-Hanger: A company that buys doors, framing, hardware, glass lites and other components and prepares or pre-hangs the unit for installation.


Pre-Shimmed Tape Sealant: A sealant having a pre-formed shape containing solids or discrete particles that limit its deformation under compression.


Prep: A cleaner or a product that enhances an adhesive; usually applied to the glass prior to the primer.


Pressed Glass: Glassware formed by placing a blob of molten glass in a metal mold, then pressing it with a metal plunger or follower to form the inside shape. The resultant piece, termed mold-pressed, has an interior form independent of the exterior, in contrast to mold blown glass, whose interior corresponds to the outer form. The process of pressing glass was first mechanized in the United States between 1820 and 1830.


Pressure Sensitive Adhesive: Adhesive which retains tack after release of the solvent so it can be bonded by simple hand pressure.


Preston Test: The means of verifying the bursting strength of a glass container during automatic inspection.


Prime Window: A primary window as opposed to a storm or combination unit added on.


Primer: An undercoat or chemical applied to a surface to improve the adhesion, durability and appearance of a topcoat or the bond of an adhesive. A product (chemical) used to prepare metal bonding areas and ensure a strong bond between the glass part and the adhesive.


Priming: Sealing of a porous surface so that compound will not stain, lose elasticity or shrink excessively. A sealant primer or surface conditioner may be used to promote adhesion of a curing type sealant to certain surfaces.


Primerless Urethane: A type of urethane adhesive that requires no primer on the glass surface. Metal primers may be necessary.


Prismatic Glazing: A daylighting device that consists of a light-redirecting glazing with a fine-structure, sawtooth cross-section, designed to refract incident sunlight and sky light toward the ceiling.


Pro Dealer: A term used for building product dealers and/or distributors that cater to professional customers such as home builders and remodeling contractors.


Production Cutters: Mechanical cutters.


Projected Window: A window fitted with one or more sashes opening on pivoted arms or hinges. The term refers to casements, awnings and hoppers.


Protected Opening: A window with a fire-resistance rating suitable for the wall in which it is located.


Psychrometric Chart: A chart which shows various psychrometric quantities, like dry bulb and wet bulb temperatures, moisture content, partial pressure of water vapor, etc.


Pultrusion: The process used to produce fiberglass composite profiles or components for the production of windows and doors. Term also is used generally to refer to the composite profiles or lineals cut and processed to make window and door components.


Pump Gun: A device used for pumping sealants and adhesives.


Push Up: The base of a glass bottle (particularly of a wine bottle) which is pushed upwards inside the bottle during the forming process.


PVC: A polymer known as polyvinylchloride made by combining several chemicals, fillers, plasticizers and pigments. It is often used as an extruded or molded plastic material for window framing or as a thermal barrier for aluminum windows.


Pyrolytic Coating: A low-E, thin-film coating applied at high temperature.


Pyrolytic Deposition: A process for applying a thin metallic coating to the surface of flat glass during the float glass manufacturing process.


Pyrolytic Glass: A glass product that is coated, usually to provide low-emissivity or solar control benefits, during the manufacturing process at the molten glass stage. Commonly referred to as a hard coat, this type of coating offers a surface that is generally as durable as an ordinary glass surface, and therefore requires no special handling and does not need to be used in an insulating glass unit. The other type of glass coating is a sputter-coat, which is applied in a secondary process. Sometimes referred to as a soft-coat, these types of coatings generally require some additional care in handling and fabrication and must be used within an insulating glass unit.


Pyrometer: An instrument used to measure the temperature inside the furnace or kiln.




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Rabbet: An ‘L’ shaped section, which can be face glazed or receive a removable glazing bead to hold the lite of glass in place.


Racking: A movement or distortion of sash or frames causing a change in angularity of corners.


Radiant Temperature: The temperature describes the infrared radiant field at a certain position and is the weighted average of surface temperatures surrounding the location; the weighting is dependent on surface emissivity and the view factors to the measurement point.


Radiant Temperature: The temperature describes the infrared radiant field at a certain position and is the weighted average of surface temperatures surrounding the location; the weighting is dependent on surface emissivity and the view factors to the measurement point.


Radiation: The transfer of heat, in the form of electromagnetic waves, from one surface to another. For example, energy from the sun reaches the earth by radiation, and a person’s body can lose heat to a cold window or skylight surface in a similar way.


Rail: A horizontal member of a window sash or door panel. Also known as head rail, top rail, bottom rail, meeting rail.


Raw Materials, for Basic Refractories: Basic refractories are made up of various mixes of periclase (magnesium oxide), chromite (chrome ore) and forsterite (olivine). Bonding agents can also be added so that refractories can be shaped.


Redox: The abbreviated form of reduction-oxidation. The term redox equilibria is used to refer to the balance between reduction and oxidation in the glass furnace.


Redox Equilibra: Used to refer to the balance between reduction and oxidation in the glass furnace.


Refining: Refining ensures that a homogenous glass is produced during founding by eliminating bubbles. Refining is achieved through the action of certain chemicals (refining agents) added to the batch recipe and also by keeping the glass above the liquids temperature so the bubbles rise to the surface.


Reflectance: The fraction of incident radiation upon a surface that is reflected from that surface.


Reflection: The process by which incident flux leaves a surface or medium form the incident side, without change in frequency.


Reflective Glass: Window glass that is coated to reflect radiation striking the surface of the glass.


Reflectivity: The reflectance of a microscopically homogeneous sample with a clean, optically smooth surface and of thickness sufficient to be completely opaque.


Refraction: The deflection of a light ray from a straight path when it passes at an oblique angle from one medium (such as air) to another (such as glass).


Refractive Index: A standard of measurement used particularly to establish the qualities of optical glass. The index is the ratio of the sine of the angle of incidence of a ray of light to the sine of the angle of refraction (the change in direction when a ray of light passes from one medium to another) by the glass. The second medium normally used to establish the index is a vacuum.


Refractories: Material capable of withstanding extremely high temperatures and thus used in furnaces for industries such as glass and steel where raw materials have to be heated to a molten form.


Regenerative Heating: As in recuperative heating, waste heat from the furnace is used to pre-heat combustion air. Regenerative heating is a cyclic process whereby exhaust gases pass over and thus heat up refractory blocks in one of two pre-heating chambers. Once the first chamber has been heated up, exhaust gases are diverted to heat the second chamber, while cold combustion gas is introduced into the first chamber to be pre-heated by the hot refractory blocks. Continuous reversal of this process provides a permanent flow of pre-heated gas for combustion.


Relative Heat Gain: The amount of heat gain through a glass product taking into consideration the effects of solar heat gain (shading coefficient) and conductive heat gain (U-value). The value is expressed in Btu/hr/ft2 (W/m2). The relative heat gain is calculated as RHG = (Summer U-value x 14oF) + (Shading Coefficient x 200). The lower the relative heat gain, the more the glass product restricts heat gain.


Relative Humidity: The percentage of moisture in the air in relation to the amount of moisture the air could hold at that given temperature. At 100 percent relative humidity, moisture condenses and water droplets are formed.


Release Agent: A liquid solvent used to soften adhesives or sealants.


Removable Double Glazing (RDG): A removable glazed panel or sash on the inside or outside of an existing sash or window, such as a storm panel, used for additional insulation and protection against the elements.


Resilience: A measure of energy stored and recovered during a loading cycle. It is expressed in percentage.


Resin Laminating: A process used to laminate curved glass and other specialized limited batch applications.


Resin: A solid organic material, generally not soluble in water, that has little or no tendency to crystallize. Resin is optically matched to auto glass and used to fill breaks and cracks. A term commonly used within the industry that refers to the raw materials used by PVC extruders to produce vinyl window profiles. The word is also used to describe a liquid material that is used in the production of laminated glass.


Retainer: An item that holds steady a panel to a frame.


Ribbon Window / Window Band: A series of windows in a row across the face of a building.


Roll (or Roller) Distortion: Waviness imparted to horizontal heat treated glass while the glass is transported through the furnace on a roller conveyor. The waves produce a distortion when the glass is viewed in reflection.


Roll Impressions: Indentations in the surface of rolled glass caused by contact of the glass with the rolls and/or displaced roll disks while the glass surface is in a plastic state.


Roll Marks / Roll Scratches: A series of the fine parallel scratches or tears on the surface of rolled glass in the direction of draw. They are 1/8″ (3 mm) long or smaller, but usually so fine and so close together that they appear to be a series of incipient checks rather than scratches. They are caused by a difference in velocity between rolls and the sheet of glass.


Rolled Glass: A flat glass with a patterned or irregular surface, produced by rolling, and having varying transparency. Types include flat wire glass, corrugated glass, patterned glass, obscured glass, cast glass, and figured glass. Rolled (or cast) glass is a translucent glass with 50-80% light transmission, depending on its thickness and type of surface. It is used where transparency of the glass sheet is not important or not desired. To produce rolled glass, molten glass pours from the melting tank over a refractory barrier (the weir) and onto the machine slab where it flows under a refractory gate (the tweel), which regulates the volume of glass, and then between two water-cooled rollers. The distance between the rollers determines the thickness of the glass.


Roll Up Shade: A window shade installed on inside of building that rolls up around a cylindrical holder at the top. These shades serve to maintain privacy, reflect some solar radiation, and reduce convection flow when fully extended.


Roof Window: A fixed or operable window similar to a skylight that is placed in the sloping surface of a roof. See also Skylight.


Rough Opening: The framed opening in a wall into which a window or door unit is to be installed.


Round Top: One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening. Also referred to as arch-tops, circle-tops and circle-heads.


Rub: A series of small scratches in glass generally caused during transport by a chip lodged between two lites.


Rubber Blocks or Spacers: Small rubber blocks/spacers, used by some manufacturers, to separate the glass from the metal frame.


R Value: The thermal resistance of a glazing system expressed ft2/hr/oF/Btu (m2/W/oC). The R-value is the reciprocal of the U-value. The higher the R-value, the less heat is transmitted throughout the glazing material.




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Safety Glass: Glass constructed, treated or combined with other materials to reduce the likelihood of injury to persons in the broken or unbroken state. Types of safety glass include laminated safety glass, tempered glass and wire glass. Glass which does not disintegrate into sharp and potentially dangerous splinters when it is broken. Safety glass may be produced by laminating (see laminated glass) or by tempering (see tempering).


Safety Glazing: See Tempered Glass.


Sand: The most common form of silica used in making glass. It is collected from the seashore or, preferably, from deposits that have fewer impurities. For most present-day glassmaking, sand must have a low iron content. Before being used in a batch, it is thoroughly washed, heated to remove carbonaceous matter, and screened to obtain uniformly small grains.


Sandblasting: A method for creating a decorative effect on glass. Sandblasting consists of blasting an abrasive at the surface of the glass under pressure. Matte and peppered effects are achieved using different pressures and shading is achieved by changing the distance and pressure of blasting during application.


Sandblasted Finish: A surface treatment for flat glass obtained by spraying the glass with hard particles to roughen one or both surfaces of the glass. The effect is to increase obscurity and diffusion, but it makes the glass weaker and more difficult to clean.


Sash: The window frame, including muntin bars if used, to receive the glazing infill. The portion of a window that includes the glass and framing sections which are directly attached to the glass. Not to be confused with the master frame into which the sash sections are fitted. An assembly of stiles and rails (vertical and horizontal members) made into a frame for holding glass.


Sash Cord: Rope or chain in double-hung windows that attaches the sash to the counter balance.


Sash Lift: Protruding or recessed handle on the inside bottom rail of the lower sash on a double or single hung window.


Sash Stiffener: A reinforcement usually inserted into a sash profile prior to assembly; Designed to increase the strength of the unit.


Sash Weights: Concealed cast-iron weights used to counterbalance the sash of older double hung windows.


Sausage Packs: A type of packaging for adhesive materials. The material is packaged in an aluminum foil pack. When the material is forced out of the package, the foil is crushed, reducing the amount of disposable waste.


Screen Printing: A process for the decoration of glass whereby colored ink is forced by a flexible squeegee through a fine-mesh screen or mask (traditionally made of silk, now also made of nylon, polyester and stainless steel) onto the glass surface. A separate mask is used for the application of each color. Considerable automation of the process has been developed, thus allowing extremely high printing speeds for even complex designs.


Score: The term used to describe a cut on the surface of glass or mirror with a glass cutter.


Scratches: Any marking or tearing of the surface appearing as though it had been done by either a sharp or rough instrument.


Screw On Bead / Applied Stop: Stop, molding or bead fastened by screws as compared with those that snap into position without additional fastening.


Sealant: A flexible material placed between two or more parts of a structure with adhesion to the joining surfaces to prevent the passage of certain elements such as air, moisture, water, dust and other matter. Sealants are commonly made of silicone, butyl tape or polysulfide.


Sealer: A surface coating generally applied to fill or protect cracks, pores or voids in a surface.


Sealed Insulating Glass Units: See Insulating Glass Unit


Seam: To grind, usually with an abrasive belt, wet or dry, the sharp edges of a piece of glass.


Seeds: Minute bubbles in float glass less than 1/32” or .8 mm in diameter.


Selective Surface: A surface for which the spectral optical properties of reflectance, absorptance, emittance, or transmittance vary significantly with wavelength, enhancing the collection (or rejection) of radiant energy in a restricted portion of the spectrum.


Self-Cleaning Glass: Glass treated with a special coating. Currently, commercially available products feature a coating that uses the sun’s UV rays to break down organic dirt through what is called a photocatalytic effect. The coating also provides a hydrophilic effect, which reduces the surface tension of water to cause it to sheet down the surface easily and wash away dirt.


Setting: Placement of lites or panels in sash or frames. Also action of a compound as it becomes more firm after application.


Setting Block: Small blocks made of neoprene, vinyl, etc, to distribute the weight of glass to the strong point of a sash or frame, to aid in centering the glass and to prevent glass-to-metal contact.


Shading Coefficient (SC): The ratio of solar heat gain through a window to the solar heat gain through a single layer of 3mm clear glass under the same environmental conditions. This is meaningful for near-normal incidence only. This quantity has been replaced by the Solar Heat Gain Coefficient (SHGC).


Shaded Glass: Laminated glass in which a dark color has been added to the top section of the inner vinyl layer to improve driver visibility in glare. The color typically becomes lighter as the tint travels down the glass.


Shadowgraph: A device for inspecting glass with respect to distortion and other defects.


Shard: A sharp piece or fragment of glass.


Shear Test: A method of deforming a sealed or bonded joint by forcing the substrates to slide over each other. Shear strength is reported in units of force per unit area (psi).


Sheet Glass: Flat glass made by continuous drawing and whose surface has a characteristic waviness. Because of the long usage of the term, much thin float glass is still incorrectly referred to as sheet glass.


Shims: See Spacers


Shore A Hardness: Measure of firmness of a compound by means of a Durometer Hardness Gauge. Shore A hardness range of 20-25 is about the firmness of an art gum eraser. A hardness of 90 is about the firmness of a rubber heel.


Short Wave Infrared Radiation: Short wave infrared radiation is from 770 nm to 2500 nm (0.77 to 2.5 microns).


Sidelites: Narrow fixed units mulled or joined to operating door units to give a more open appearance.


Sidelighting: Lighting from windows and translucent walls. Sidelighting historically was encouraged by the need for exterior views as well as light, and is best accomplished in buildings with narrow plans.


Sight Line: The line along perimeter of glazing infills corresponding to the top edge of stationary and removable stops. The line to which sealants contacting the glazing infill are sometimes finished off.


Silicone Sealant: A sealant having as its chemical composition a backbone consisting of alternating silicon oxygen atoms.


Simulated Divided Lites (SDLs): A type of grille or grid design that creates the appearance of a number of smaller panes of glass separated by muntins, but actually uses larger lites of glass with the muntins placed between and/or on the surfaces of the glass layers.


Single Glazing: Use of a single lite of glass in a window; generally not as energy efficient as insulating glass or other forms of double glazing.


Single Seal Units: IG unit manufactured with only one sealant.


Single Hung: A window resembling a double hung or vertically sliding window, with a fixed, non-operating top sash.


Single Strength Glass: Glass with thickness between 0.085 and 0.100 inch.


Silica: Silicon dioxide, a mixture that is the main ingredient of glass. The most common form of silica used in glassmaking has always been sand.


Silicone: A chemical used as a lubricant or as a sealant with a wide variety of usage.


Silk Screen Process: A decorating process in which a design is printed on glass through a silk mesh, woven wire or similar screen.


Sill: The lowest horizontal member in a door, window, sash, or ventilator frame. Also known as sill plate, inside sill, outside sill.


Sill Pan: A product placed under a window or door during the installation process that is designed for water drainage.


Single Glazed / Single Glazing: Glazing that is just one layer of glass or other glazing material (as opposed to sealed insulating glass which offers far superior insulating characteristics).


Single Hung Window: A window consisting of two sashes, the top one stationary and the bottom movable. This window is similar to a double-hung window except that the top sash is stationary. See also Double hung window.


Skin: A single piece of material used as the face of a door.


Skinned Over: The appearance of an adhesive when it has started to cure.


Skylight: A sloped or horizontal application of a fenestration product which allows for daylighting. Skylights may be either fixed (non-operable) or venting (operating). Unlike roof windows, skylights need not provide provisions for the cleaning of exterior surfaces from the interior of the building.


Slab: A term for a complete door panel that has not been prepared for installation into a frame.


Sliding Window: A window fitted with one or more sashes opening by sliding horizontally or vertically in grooves provided by frame members. Vertical sliders may be single or double hung.


Sloped Glazing: A glass and framing assembly that is sloped more than 15 degrees from the vertical and essentially forms the entire roof of the structure. This is generally a single-slope construction. Also, any glazed opening in a sloped roof or wall, such as a stationary skylight or fully operable roof window.


Smart Window: The generic term for windows with switchable coatings to control solar gain.


Smoke: Streaked areas appearing as slight discoloration on glass.


Soda: Sodium carbonate. Soda (or alternatively potash) is commonly used as the alkali ingredient of glass. It serves as a flux to reduce the fusion point of the silica when the batch is melted.


Soda Ash: Sodium carbonate (Na2CO3), or soda ash, is the main source of sodium oxide (Na2O), or soda. This anhydrous white powder is added to the glass batch with sodium oxide becoming part of the glass and carbon dioxide being released.


Soda Lime Glass: The most common type of industrially produced glass. A typical soda-lime glass is composed of silica (71-75%), soda (12-16%) and lime (10-15%), plus small amounts of other materials to provide particular properties such as color.


Soft Coat(ing): Generally refers to silver-based, low-E coating; see above. So called due to its susceptibility to damage through abrasion. The coating generally consists of a multilayer structure of alternate dielectric and thin transparent metal layers which are deposited in a vacuum chamber. Also known as sputtered coating.


Soft Coat Glass: A glass product that is coated in a secondary process known as sputter-coating, usually to offer low-emissivity or solar control benefits. The term refers to the fact that these types of coatings generally require some additional care in handling and fabrication and must be used within an insulating glass unit. A hard coat or pyrolytic glass is coated during the manufacturing process at the molten glass stage. This type of coating offers a surface that is generally as durable as an ordinary glass surface and therefore requires no special handling and does not need to be used in an insulating glass unit.


Solar Absorptance: The fraction of incident solar radiation absorbed by glazing.


Solar Control Coatings: Thin film coatings on glass or plastic that absorb or reflect solar energy thereby reducing solar gain.


Solar Control Glass: Tinted and/or coated glass that reduces the amount of solar heat gain transmitted through a glazed product.


Solar Control Glazing: Glazing modified to reduce its total solar energy transmittance by means of tinting, selective surface coating, or the application of a retrofit film.


Solar Energy Reflectance: In the solar spectrum, the percentage of solar energy that is reflected from the glass surface(s).


Solar Energy Transmittance: The percentage of ultraviolet, visible and near infrared energy within the solar spectrum (300 to 2100 nanometers) that is transmitted through the glass.


Solar Glass: Glass that either reflects or absorbs the ultraviolet and infrared rays from the sun.


Solar Heat Gain: Heat from solar radiation that enters a building.


Solar Heat Gain Coefficient (SHGC): The fraction of solar radiation admitted through a window or skylight, both directly transmitted and absorbed and subsequently released inward. The solar heat gain coefficient has replaced the shading coefficient as the standard indicator of a windows shading ability. It is expressed as a number between 0 and 1. The lower a windows solar heat gain coefficient, the less solar heat it transmits, and the greater its shading ability. SHGC can be expressed in terms of the glass alone or can refer to the entire window assembly. For near-normal incidence only, SHGC = 0.86 x SC.


Solar Radiation: The total radiation of energy from the sun, including ultraviolet and infrared wavelengths as well as visible light.


Solarization: Change in transmission, and sometimes color, of plastics as a result of exposure to sunlight or other radiation.


Sound Insulating / Sound Resistive Glass: Glazing that is fixed on resilient mountings and separated so as to reduce sound transmission.


Sound Transmission Class (STC): A single number rating calculated in accordance with ASTM E 413 using sound transmission loss values. It provides an estimate of the sound insulation performance of an interior partition in common sound insulation situations. The frequency range used is typical of indoor office noises.


Sound Transmission Loss (STL): The reduction of the amount of sound energy passing through a wall, floor, roof, etc. It is related to the specific frequency (Hz) at which it is measured and it is expressed in decibels (dB). Also called Transmission Loss (TL).


Spacer: The linear object that separates and maintains the space between the glass surfaces of insulating glass.


Spacer, Flat: Small blocks of composition, neoprene, etc., placed on each side of lites to center the lites in the channel and maintain uniform width of sealant beads. They prevent excessive sealant distortion.


Spall: Spalling occurs as shards of glass break away from the rear face (protection side) of a laminate as a result of impact, often becoming dangerous projectiles themselves.


Spandrel: An exterior wall panel filling the space beneath a window sill that usually extends to the top of the window below in multistory construction.


Spandrel Glass: Architectural glass that is used in spandrel panels.


Spectrally Selective Coating: A low-E coating with optical properties that are transparent to some wavelengths of energy and reflective to others. Typical spectrally selective coatings are transparent to visible light and reflect short-wave and long-wave infrared radiation.


Spectrally Selective Tint: A tinted glazing with optical properties that are transparent to some wavelengths of energy and reflective to others. Typical spectrally selective tints are transparent to visible light and reflect short-wave and long-wave infrared radiation.


Spectrally Selective Glazing: A specially engineered low-E coated or tinted glazing whose optical properties vary with wavelength.


Specular Surface: A mirrored surface which reflects light at the same angle as the light falling on the surface.


Spinning, Hollow Ware: A relatively new method for the centrifugal production of hollow ware such as borosilicate glass columns in chemical plants, funnels, television tubes and other non-rotationally symmetrical items. Molten glass is fed into a steel mould which rotates at the required speed. At high speeds, the glass can assume almost cylindrical shapes. When the glass has cooled sufficiently, rotation stops and the glass is removed.


Splayed Window: Window unit set at an angle in a wall.


Sputter Coating: A secondary manufacturing process in which a thin layer of materials, usually designed to offer low-emissivity or solar-control benefits, is applied to glass. Sputter coatings are commonly referred to as soft coats, as they generally require some additional care in handling and fabrication and must be used within an insulating glass unit. A hard coat or pyrolytic glass is coated during the manufacturing process at the molten glass stage. This type of coating offers a surface that is generally as durable as an ordinary glass surface and therefore requires no special handling and does not need to be used in an insulating glass unit.


Stain: Discoloration of either a glass or finished aluminum surface caused by alkalis that leach from surrounding materials such as pre-cast or cast-in-place concrete or from sealants, pollutants or other contaminants.


Stained: See Decorative Glass


Staple Fiber: Short lengths of glass fiber, usually U-shaped, which intertwine and are used, in particular, to create insulation materials.


Stemware: The collective term given to drinking glasses whose body is connected to the base by a thinner column of glass.


Stile: The main vertical members of the framework of a sash or door panel.


Stile-and-Rail Door: Traditional type of wood door constructed with vertical stiles and rails with openings filled with raised wood panels or glass.


Stoce: Unit of glass sheets transported without benefit of a wood crate.


Stones: Any crystalline inclusion imbedded in the glass.


Storefront: A nonresidential system of doors and windows mulled as a composite structure. Typically designed for high use/abuse and strength. The storefront system is usually installed between floor and ceiling.


Stool: Interior trim piece sometimes used to extend a window sill and act as a narrow shelf.


Storm Door: A panel or sash door placed on the outside of an existing door to provide additional protection from the elements.


Storm Window: A glazed panel or sash placed on the inside or outside of an existing sash or window as additional protection against the elements.


Stop: A molding used to hold, position or separate window or door parts. Also, the molding or component on the inside of a window frame against which the window sash rests or closes. Also called a bead, side stop, window stop and parting stop.


Straightedge: A piece of material with a straight edge for testing straight lines and surfaces or drawing straight lines.


Straight-Jaw Glass Pliers: Glass pliers that have identical upper and lower jaws.


Strain: The percentage of elongation or compression of a material or portion of a material caused by an applied force.


Strain Pattern: A specific geometric pattern of iridescence or darkish shadows that may appear under certain lighting conditions, particularly in the presence of polarized light (also called quench marks). The phenomenon is caused by the localized stresses imparted by the rapid air cooling of the tempering operation. Strain pattern is characteristic of heat treated glass.


Stress / Residual: Any condition of tension or compression existing within the glass, particularly due to incomplete annealing, temperature gradient or inhomogeneity.


Stress Cracks: Cracks resulting from unusual forces acting on the glass body.


Striking Off: The operation of smoothing off excess compound or sealant at sight line when applying same around lites or panels.


Structural Glass: Flat glass that is usually colored or opaque and frequently ground and polished, used for structural purposes. Glass block, usually hollow, that is used for structural purposes.


Structural Glazing: Glazing which is part of the structural design of a building.


Structural Glazing Gaskets: Cured elastomeric channel shaped extrusions used in place of a conventional sash to install glass products onto structurally supporting sub-frames, with the pressure of sealing exerted by the insertion of separate lockstrip wedging splines.


Structural Silicone Glazing: The use of a silicone sealant for the structural transfer of loads from the glass to its perimeter support system and retention of the glass in the opening.


Substrate: The underlying hard structure supporting a special purpose surface treatment (e.g. thin-film coating).


Suck-Blow Process: A process used for glass container manufacturing with forming machines. Glass is sucked from the tank of molten glass into the parison mould and then cut by shears. A plunger inside the mould produces a hollow space in the glass which is then enlarged by blowing. Following this initial blow and then reheating, the parison is transferred to the finishing mold for the finishing blow.


Suction Cup: A semi-spherical cup of flexible material such as rubber. By pressing the cup onto a glass surface and removing air from inside the cup, the vacuum thus created holds the cup and glass together. Suction cups are used in both the manual and automatic handling and conveyance of glass.


Sun Control Film: A tinted or reflective film applied to the glazing surface to reduce visible, ultraviolet, or total transmission of solar radiation. It reduces solar heat gain and glare and, in some cases, can be removed and reapplied with changing seasons.


Sun Scoops: Clerestory roof monitors oriented toward the sun, utilized when and where capturing direct light or solar gains are desired.


Super Window: A window with a very low U-factor (typically less than 0.15) achieved through the use of multiple glazings, low-E coatings and gas fills.


Surface Coating: The deposition of a thin-film coating on a surface.


Suspended Film: Polymer-based, optically clear glazing layer mounted between glass layers in a multiple glazed system.


Suspended Glazing: Glazing system suspended from above. This innovation, first achieved in projects of the 1960s, made possible continuous glass facades, without mullions.


Suspended Particle Device (SPD): A type of switchable glazing that typically uses laminated glass construction with the interlayer material featuring suspended particles that align when the glass unit is charged to provide a clear view and scatter when there is no charge, changing the glazing to translucent.


Switchable Glazings: Glazings with optical properties that can be reversibly switched from clear to dark or reflective with the application of an external stimulus, e.g. heat, light, electric signal, etc. Also known as dynamic glazing.




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Tack / Tackiness: The stickiness of the surface of a sealant or adhesive.


Tank: A large receptacle constructed in a furnace for melting the batch. Tanks replaced pots in larger glass factories in the 19th century.


Tape Glazing: Installing glass or products with butyl tape.


Tape Sealant: A sealant having a preformed shape and intended to be used in a joint under compression.


Tapping Ball: An added feature to a wheel cutter that is used to weaken the glass on the underside of the score line prior to breaking.


Task Lighting: Light used to illuminate visually demanding activities, such as reading.


Tempered Glass: Treated glass that is strengthened by reheating it to just below the melting point and suddenly cooling it. When shattered, it breaks into small pieces. Since these particles do not have the sharp edges and dagger points of broken annealed glass, tempered glass is regarded as a safety glass and safety glazing material. Tempered glass is also approximately five times stronger than standard annealed glass. The glass must be cut to size and have any other processing (such as edge polishing and hole drilling) completed before being subjected to toughening, because attempts to work the glass after tempering will cause it to shatter. Also known as toughened glass.


Tempering: Strengthening glass with heat.


Tenon: A rectangular projection cut out of a piece of wood for insertion into a mortise.


Tensile Strength: Resistance of a material to a tensile force (a stretch). The cohesive strength of a material, expressed in psi.


Tension: The act of straining or stretching.


Thermal Barrier / Thermal Break: An element, made of a material with relatively low thermal conductivity, which is inserted between two members having high thermal conductivity in order to reduce the heat transfer. Such elements are often used in aluminum windows.


Thermal Break: A thermally insulating or low-conductance material used between interior and exterior aluminum (or other conductive materials) window and door components.


Thermal Conductance: The same as thermal conductivity except that thickness is ‘as stated’ rather than one inch.


Thermal Conduction: The mode of heat transfer through a material by molecular contact. Heat flows from a high temperature area to one of lower temperature.


Thermal Conductivity: The heat transfer property of materials, expressed in units of power per area and degree of temperature (e.g. BTU-per-hour per inch of thickness per square foot of surface per one degree F temperature difference). The passage of heat through a material. Insulation materials are defined as having low thermal conductivity whereas metallic materials generally have high thermal conductivity.


Thermal Emissivity: Similar to thermal emittance, except that the suffix ‘-ivity’ refers to a property of general material, while ‘-ance’ refers to a specific material with a certain thickness, surface finish, etc.


Thermal Emittance: The ability of a surface to emit long-wave radiation relative to that of a perfect black body. Also known as the long-wave infrared emittance. A perfect black body has an emittance equal to 1.0, while a perfect reflector has an emittance equal to zero.


Thermal Endurance: The relative ability of glass to withstand thermal shock.


Thermal Mass: The mass in a building (furnishings or structure) that is used to absorb solar gain during the day and release the heat as the space cools in the evening.


Thermal Movement: Movement and changes in a structure caused by temperature changes.


Thermal Radiation: The heat transfer by radiation from surfaces at or near the room temperature (i.e., wavelengths in the range 2.5 – 50 microns). It is often referred to as far IR radiation or long-wave IR radiation.


Thermal Resistance: A property of a substance or construction which retards the flow of heat; one measure of this property is R-value.


Thermal Shock: A rapid change in temperature imposed on a glass body.


Thermal Shock Testing: Assessing the effects on a material of rapid temperature change. In glass, the shock may derive from the external surface of glass expanding or contracting more rapidly than the interior surface as a result of heating or cooling. Any such difference may lead to cracking or shattering.


Thermal Stress: Stress caused by the temperature differential across a glazing layer; e.g. for a tinted or switchable glazing in its darkened state, the sunlit side of the glazing will be hotter than the reverse side.


Thermocouple: A pair of different metals in contact at a point, generating a thermoelectric voltage which can serve as a measure of temperature.The wires are encased in a protective sheath that can be introduced as a probe into the glass furnace or kiln.


Thermochromic Glazing / Thermochromics: Glazing which changes its thermal, solar, and visible transmittance in response to its temperature. Because of absorption, the temperature of the glazing may differ from the ambient temperature.


Thermogram: An image of an object taken with an infrared camera that shows surface temperature variation.


Thixotropic: Non-sagging. A material which maintains its shape unless agitated. A thixotropic sealant can be placed vertically in a joint and will maintain its shape without sagging during the curing process.


Tilt Window: A single or double hung window whose operable sash can be tilted into a room to allow cleaning of the exterior surface on the inside.


Tin Side: Also called the non-air side, the surface of glass facing the molten tin within a float glass furnace.


Tinted Glass: Glass that is colored by incorporation of a mineral admixture, by surface coating, or by the application of retrofit film. Any tinting reduces both visual and radiant transmittance.


Toe Bead: Sealant applied at the intersection of the outboard glazing stop and the bottom of the glazing channel; must be sized to also provide a seal to the edge of the glass.


Tong Marks: Small, surface indentations near and parallel to one edge of vertically tempered or vertically heat strengthened glass resulting from the tongs used to suspend the glass during the heat treating process.


Tooling: The pressing of a compound in and against the side of a joint to form good adhesion; also dressing of a joints surface compound for good appearance.


Toplighting: Lighting from skylights, roof monitors or clerestories. Toplighting historically has been utilized when floor areas are too large to be illuminated adequately by sidelighting.


Toughening: Special process of solidification of a glass sheet in order to make it particularly resistant to breakages. The process may be physical (thermal) or chemical. In the former, the glass sheet is heated to a temperature just below its softening point and then immediately cooled by special jets of cold air. These harden the surface of the glass, giving the inside more time to cool. This allows the external layer to crystallize into a wider lattice while the inside solidifies with greater compression than in the crystal lattice. The result is a sheet of glass which is two or three times stronger than untempered glass and which, upon breakage, shatters into tiny pieces with blunt edges (the most common applications are for automotive or safety glass). The chemical process, on the other hand, is based on the so-called ion-stuffing technique. Different chemical elements possess different ionic radii and therefore different densities. Hence, if glass containing sodium is cooled slowly in a salt bath of molten potassium, the sodium ions will migrate from the glass to the salt, while the potassium ions will move to the surface of the glass where, due to their wider radium, they create a denser and therefore stronger surface layer (of no less than 0.1 mm). Glass sheets which have been chemically tempered are five to eight times stronger than those which have not undergone any tempering process.


Toxic: Poisonous or dangerous to humans if swallowed or inhaled, or by contact, possibly resulting in eye or skin irritation.


Toxicity: The level or poisonous or toxic effect of a material.


Translucent: Permitting light to pass through, but with differing degrees of obscuration and diffusion.


Transmission: The quantity of heat flowing through a unit area due to all modes of heat transfer induced by the prevailing conditions.


Transmittance: The percentage of radiation that can pass through glazing. Transmittance can be defined for different types of light or energy, e.g. visible light transmittance, UV transmittance or total solar energy transmittance.


Transom Window / Transom Light: The window sash located above a door.


Transparent: Permitting light to pass through with clear vision.


Transparent Insulation Material (TIM): A generic name for a class of glazing materials having high visible transmittance and very low thermal transmittance. Includes so-called geometric media (honeycomb structures, aerogels, etc.). Some TIMs are translucent (diffusely transmitting) rather than transparent.


Triple Glazing / Triple Pane Glass: A window with three panes of glass or two outer panes of glass with a suspended plastic film in between. The layers are separated by two gas filled spaces (usually Argon or Krypton) to increase energy efficiency and provide other performance benefits.



True Divided Lites (TDLs): Traditional window construction incorporating smaller panes of glass actually separated by muntins, rather than simulating such an appearance with larger lites of glass and a muntin grid or grille placed between or on the surfaces of the glass layers.


Tube Drawing Process: See Danner Process


Tubing: Hollow rods of glass used especially in the production of laboratory/medical equipment (ampoules, vials, etc.) and fluorescent lighting.


Turret Cutter: A cutter head with more than one cutting wheel.


Two Part Adhesive / Urethane: A type of adhesive that has two component parts: Hardener and resin. In auto glass adhesives, there are two-part urethanes and two-part adhesives. Although they are different chemically, they do have similar performance characteristics.


Two Part (Multi-Component) Sealant: A product comprised of a base and curing agent or accelerator, necessarily packaged in two separate containers, which are uniformly mixed just prior to use.


Two Step Distributor: An industry term for a wholesale company that buys building products from the manufacturer and sells them to lumberyards and home centers, which in turn sell to builders, contractors and homeowners. A wholesaler that buys building products from a manufacturer and sells them to builders, contractors and homeowners is referred to as a one-step distributor.




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UBC: Uniform Building Code.


U Factor / U Value: The heat transmission in unit time through unit area of a material or construction and the boundary air films, induced by unit temperature difference between the environments on each side. A measure of the rate of non-solar heat loss or gain through a material or assembly. The lower the U-factor, the greater a window’s resistance to heat flow and the better its insulating value.


U-Factor (total): The area-weighted average thermal transmittance of a complete window, including center-of-glass, edge-of-glass and frame U-factors.


Ultraviolet Light (UV): Invisible rays of solar radiation at the short-wavelength violet end of the spectrum. Ultraviolet rays can cause fading of paint finishes, carpets and fabrics, as well as deterioration of some materials.


Ultraviolet Radiation (UV): Extremely short wavelength invisible radiation at the violet end of the visible spectrum. UV rays are found in everyday sunlight and can cause fading, chalking of dark paint finishes, or other damage. Extreme UV exposure can cause certain plastic materials to distort and can cause sunburn.


Ultraviolet Transmittance Weighted: A measure of non-visible solar transmittance between 280 and 380 nanometers in wavelength.


Ultimate Elongation: Elongation at failure.


Uniform Bead: A consistent width and appearance of a substance (adhesive) applied to a surface.


Unit: Term normally used to refer to one single assembly of insulating glass.


United Inches: Total of one width and one height of a lite of glass in inches.


Unleaded Frit: A painted band around the perimeter of the glass applied with unleaded paint. It requires special preparation before bonding.


Urethane Breakdown: Results when urethane is exposed to ultra-violet light. Urethane breakdown appears as a chalky black powder on the surface of the hardened adhesive.


Urethane: A family of polymers ranging from rubbery to brittle. Usually formed by the reaction of a diisocyanate with a hydroxyl; also called polyurethane.


U Value: A measure of air-to-air heat transmission (loss or gain) due to the thermal conductance and the difference in indoor and outdoor temperatures. As the U-value decreases, so does the amount of heat that is transferred through the glazing material. The lower the U-value, the more restrictive the fenestration product is to heat transfer. Reciprocal of R value.




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Vacuum Cup: A tool used for picking up glass.


V Bead: Sealant or adhesive compound applied in a triangular shape to a surface.


Vacuum / Sputtering Deposition: A process in which glass is placed in a vacuum chamber, electric energy is added, and a magnetic reaction takes place that causes the metal atoms to strike the surface of the glass at high speeds.  The atoms coat the surface of the glass uniformly.


Vacuum Glazing Window: See Evacuated Glazing


Vapor Barrier: A membrane or coating which resists the passage of water vapor from a region of high vapor pressure to low pressure, more accurately called a vapor retarder.


Vapor Deposition of Thin Films: The term covers a wide range of techniques for applying a thin film on the surface of the glass to change its technical or aesthetic properties e.g. scratch resistance, solar control. The methods employed to deposit the film include spraying onto hot glass, condensation in a vacuum and evaporation of the film material by heating.


Vapor Retarder: A material (usually in the form of a membrane or coating) that reduces the diffusion of water vapor across a building assembly, from a region of high vapor pressure to low vapor pressure.


Vello Process: A drawing process used for the production of glass tubing. Glass from the furnace forehearth flows down through an orifice (ring) within which is a rotating conical-ended shaft (or mandrel) over and around which the glass flows. The tube-shaped glass is pulled from the end of the shaft by a tractor machine and turned through 90° into a horizontal position ready for cutting.


Venetian Blind: A light controlling shading device consisting of overlapping thin, horizontal slats which can be raised or adjusted from wide open to closed positions by varying the tilt of the slats.


Venturi Tubes: Short pieces of narrow tube between wider sections of tube, used for exerting suction or measuring flow rates and invented by the Italian physicist G. B. Venturi, who died in 1822.


Vertical Run Guide: A weather strip or channel that steers the door glass in the frame when the glass is raised or lowered.


Vertical Tempering: When the glass is supported by tongs as it moves vertically through a tempering furnace.


Vial: A small cylindrical glass vessel especially for holding liquid medicines.


Vinyl: Generic term for polyvinylchloride or PVC, an extruded material used for window and door framing.


Vinyl Clad Window: A window with exterior wood parts that are covered with extruded vinyl.


Viscosity: The quality or state of being viscous; the physical property of a liquid or semi-liquid that enables it to develop and maintain a certain amount of shearing stress dependent upon the velocity of flow and then to offer continued resistance to flow.


Visible Light: The portion of the electromagnetic spectrum yielding light that can be seen. Wavelengths range from 380 to 720 nanometers.


Visible Light Reflectance: The percentage of visible light (390 to 770 nanometers) within the solar spectrum that is reflected from the glass surface.


Visible Transmittance (VT): The fraction of visible radiation transmitted by a glazing system between the limits of 380 and 770 nanometers (0.38 – 0.77 micrometers). It is weighted according to the photopic response of the human eye (V-lamdba curve) and is expressed as a number between 0 and 1. Also known as visible light transmittance (VLT). The percentage of visible light (390 to 770 nanometers) within the solar spectrum that is transmitted through glass.


Visible Reflectance: The measured amount of energy in the visible wavelength range that is reflected by a window system; it is expressed as a percentage.


Visible Spectrum: That portion of the total radiation that is visible to the human eye and which lies between the ultraviolet and infrared portions of the electromagnetic spectrum. The colors associated with the visible spectrum range from violet, indigo, blue, green, yellow, orange, through red.


Visual Comfort: A set of qualities associated with the amenity of a window, such as freedom from glare and excessive contrast.


V Lambda Curve / Photopic Response Function: A bell-shaped function describing the relative response of the human eye to solar radiation as a function of wavelength under bright light conditions.


Vulcanization: A process in which rubber is treated with chemicals to harden and strengthen it.




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Warm Edge: Term used to describe technology that uses insulating spacers to achieve better thermal performance of an insulating glass unit, particularly evident in the increase of edge surface temperatures on the indoor side in the winter.


Waste Gas Analysis: Gases emitted by the melt in the furnace can be analyzed either in the furnace itself (in order to assess melting efficiency, for example) or as they are discharged from the furnace stack (above all, for pollution control purposes). Furnace gas testing may be performed with Orsat equipment (gases are absorbed selectively as they pass through a series of specific solvents) or by means of instrumental analysis. Paramagnetic detection may be used for oxygen analysis, and infrared absorption for carbon dioxide analysis. Mass spectrometry or gas chromatography are also used to analyze gas mixtures.


Waste Heat Recovery: An economy measure whereby the heat of exhaust gases is used in a cyclic process to pre-heat combustion air and/or fuel-gas.


Wave: An optical effect in flat glass due to irregularities in the surface of the glass that make objects viewed at various angles appear wavy or bent.


Weathering: Changes on the surface of glass caused by chemical reaction with the environment. Weathering usually involves the leaching of alkali from the glass by water, leaving behind siliceous weathering products that are often laminar.


Weatherometer: An environmental chamber in which specimens are subjected to water spray and ultraviolet light.


Weatherstrip / Weatherstripping: A strip of resilient and flexible material for covering the joint between the window sash and frame in order to reduce air leaks and prevent water from entering the structure. Also, the process of applying such material.


Wedge Glazing: Interior, flexible, continuous, pressure fit gasket that ensures a high compression seal between the glass and aluminum, while applying pressure and seal to the outside architectural glazing tape.


Weeps / Weep Hole: A small opening in a window or sill member through which water may drain to the building exterior.


Weld: A term used for a type of corner construction, used with vinyl and other types of windows and doors, in which a small amount of material at the two pieces are melted or softened, then pushed together to form a single piece. This also is referred to commonly as a fusion-weld.


Wet Glazing: A method of sealing glass in a frame by use of sealants rather than dry-glazing gaskets.


Wet Seal: Application of an elastomeric sealant between the glass and sash to form a weather-tight seal.


Wheel Cutter: The most common type of hand glass cutter.


Wind Load: Force exerted by winds on building panels and complete structures; may be inward (positive) or outward (negative).


Window: The frame, equipped with sash(es), ventilator(s) or louvers, if any, and their fittings, which, when glazed with glass or substitute for it, closes an opening for the admission of air and/or light in the wall of a building.


Window-to-Wall Ratio (WWR): The ratio of the total area of a building facade which is occupied by windows (glass area and frame).


Window Unit: A complete window with sash and frame.


Window Wall: A metal curtain wall of the commercial type in which windows are the most prominent element.


Wind Pressure: The pressure produced by stopping the wind velocity; the main cause of air infiltration.


Wire Glass: A glass with inner wire mesh for strength and fire-retardant qualities.


Wired Glass: Flat rolled glass reinforced with wire mesh and used especially for glass doors and roofing to prevent objects from smashing through the glass and also to hold pieces of broken glass together. By holding the glass together, it can also protect against break-in and the spreading of fire.

Wired glass is produced by continuously feeding wire mesh from a roller into the molten glass ribbon just before it undergoes cooling.


Work Life: The time during which a curing sealant (usually two compounds) remains suitable for use after being mixed with a catalyst.



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Xerogel: A type of transparent insulation material similar to aerogel but simpler to manufacture. It has both a higher visible transmittance and higher thermal conductivity than aerogel.



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Zenith: The point on the skydome directly overhead, a 90 degree solar altitude.


Zebra Board: A board with alternating black and white diagonal lines used to observe optical transmission and reflection qualities in coated and uncoated glass.