Acoustics - The science of sound and sound control. Adhesion - The property of a coating or sealant to bond to the surface to which it is applied.Adhesive Failure - Loss of bond of a coating or sealant from the surface to which it was applied.Air Infiltration - The amount of air leaking in and out of a building through cracks in walls, windows and doors.

Air Side - In reference to float glass, the side that was up or exposed to the "air" when it was manufactured. The bottom side is referred to as the "tin" side because it floated on a liquid tin bath. Coatings are applied to the air side.

Air Spacer - An aluminum or stainless steel frame (desiccant filled) used to separate two lites of glass in an insulating unit.

Annealed - Raw glass with low, residual stresses. This enables cutting and fabrication. Annealing - In the manufacturing of float glass, it is the process of controlled cooling done in a lehr to prevent residual stresses in the glass. Re-annealing is the process of removing objectionable stresses in glass by re-heating to a suitable temperature followed by controlled cooling.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.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. Argon Gas - An invisible, non toxic gas used in insulating units to enhance the units insulating performance (u-value). Aspect Ratio - The quotient of the long side of a glazing lite over the short side of that lite.

Autoclave - A vessel that employs high pressure and heat. In the glass industry, used to produce a bond between glass and PVB or urethane sheets, thus creating a laminated glass product Backer Rod - A polyethylene or polyurethane foam material installed under compression and used to control sealant joint depth, provide a surface for sealant tooling, serve as a bond breaker to prevent three-sided adhesion, and provide an hour-glass contour of the finished bead.Bead - An applied sealant in a joint irrespective of the method of application, such as caulking bead, glazing bead, etc. Also a molding or stop used to hold glass or panels in position.Bent Glass - Flat glass that has been shaped while hot into curved shapes.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 process of edge finishing flat glass to a bevel angle.Bite - The dimension by which the framing system overlaps the edge of the glazing infill.

Blast Resistant Glass - A laminated glazing construction commonly specified to mitigate injuries from flying glass resulting from an air-blast explosive. Breather Tube Units - 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. Consult IG unit fabricator.Bubbles - In laminated glass, a gas pocket in the interlayer material or between the glass and the interlayer. In float glass, a gaseous inclusion greater than 1/32" (.8 mm) in diameter.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 Resistant Glass - A multiple lamination of glass or glass and plastic that is designed to resist penetration from medium-to-super-power small arms and high-power rifles. Buttering - Application of sealant or compound to the flat surface of some member before placing the member in position, such as the buttering of a removable stop before fastening the stop in place. Butt Glazed - The installation of glass products where the vertical glass edges are without structural supporting mullions.

Butyl - Shortened term for polyisobutylene. The primary seal of an insulating unit and key component in restricting moisture vapor transmission. Capillary Tube - A small tube factory-placed into the air spacer of an insulating unit used for balancing interior and exterior pressures during transportation over higher elevations, i.e. mountain ranges or air transport. Caulk - (v) The application of a sealant to a joint, crack or crevice. (n) A compound used for sealing that has minimum joint movement capability; sometimes called low performance sealant.

Ceramic Frit - A ceramic frit enamel applied to glass for decorative/aesthetic appearances. Applied with a large roller for full coverage applications or through a screen for silkscreening applications. 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. Chemically Strengthened Glass - Glass that has been strengthened by ion-exchange to produce a compressive stress layer at the treated surface.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.Clips - Wire spring devices used to hold glass in rabbeted sash, without stops, and face glazed. Coated Glass - A general reference to any glass incorporting a reflective or low-e coating.Cohesive Failure - Internal splitting of a compound resulting from over-stressing of the compound.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.Compound - A chemical formulation of ingredients used to produce a caulking, elastomeric joint sealant, etc. Condensation - The appearance of moisture (water vapor) on the surface of an object caused by warm moist air coming into contact with a colder object.

Conventionally Glazed - A framing system that captures the glazing component in the glazing channel. Crush - A lightly pitted area on glass resulting in a dull gray appearance.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.Cut Sizes - Glass cut to specified width and length.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 an applied load.Delamination - An unbonded area in laminated glass between glass and PVB. Design Pressure - Specified pressure a product is designed to withstand.Diffusing - Scattering, dispersing, as the tendency to eliminate a direct beam of light.Digs - Deep, short scratches. Desiccant - Small, extremely porous beads used to absorb moisture in the sealed air spacer of an insulating unit.

Distortion - General areas of optical deviation or image deformation as seen looking at the glass. Double Glazing - In general, any use of two lites of glass, separated by an air space, within an opening, to improve insulation against heat transfer and/or sound transmission. In insulating glass units the air between the glass sheets is thoroughly dried and the space is sealed, eliminating possible condensation and providing superior insulating properties.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. Double Laminated Insulating Glass - An insulating glass unit in which both the interior and exterior components are a laminated glass.

Double Strength - Refers to clear 1/8" (3mm) thick float glass.

Dual Seal - Refers to an insulating unit with a primary seal of polyisobutylene (butyl) and a secondary seal of silicone. Durometer - The measurement of hardness of a material. A gauge to measure the hardness of an elastomeric material.Edge Clearance - Nominal spacing between the edge of the glass product and the bottom of the glazing pocket (channel).Edging - Grinding the edge of flat glass to a desired shape or finish.Elastomer - An elastic, rubber-like substance, such as natural or synthetic rubber.Elastomeric - (adj) Having the property of returning to its original shape and position after removal of load. (n) An elastic rubber like substance. Emissivity - The measure of a surface's ability to emit long-wave infrared radiation.

Etch - To alter the surface of glass with hydrofluoric acid or other caustic agents. Permanent etching of glass may occur from alkali and other runoff from surrounding building materials.

European U-Value (formerly K-Value) - Based on ISO-DP10292 draft standard conditions. It is based on an outdoor temperature of 5.5°C, and indoor temperature of 20.5°C and a 4.8 m/s outdoor air velocity Exterior Glazed - Glazing infills set from the exterior of the building.Exterior Stop - The molding or bead that holds the lite or panel in place when it is on the exterior side of the lite or panel.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.Fenestration - Any glazed panel, window, door, curtain wall or skylight unit on the exterior of a building.Fillet Bead - Caulking or sealant placed in such a manner that it forms an angle between the materials being caulked.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 - That property of materials or their assemblies that prevents or retards the passage of excessive heat, hot gases or flames under conditions of use.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).Flare - A protrusion on the edge of a lite of glass.Flat Glass - A general term that describes float glass, sheet glass, plate glass and rolled glass. Float Glass - Raw glass, float refers to the process in which the glass was made. Flush Glazing (Pocket Glazing) - The setting of a lite of glass or panel into a four-sided sash or frame opening containing a recessed "U" shaped channel without removable stop on three sides of the sash or frame and one channel with a removable stop along the fourth side.Frosted Finish - A surface treatment for glass, consisting of an acid etching of one or both surfaces that diffuses transmitted light and reduces glare. Fully Tempered Glass (FT) - Glass that has been heat-treated to have either a minimum surface compression of 10,000 psi or an edge compression not less than 9,700 psi in accordance with the requirements of ASTM C 1048, kind FT or meet the requirements of ANSI Z97.1 or CPSC 16 CFR 1201 safety glazing standards. Tempered glass is 4-5 times stronger than annealed glass, and when broken, breaks into small, relatively harmless, pieces. Flush Glazing (Pocket Glazing) - The setting of a lite of glass or panel into a four-sided sash or frame opening containing a recessed "U" shaped channel without removable stop on three sides of the sash or frame and one channel with a removable stop along the fourth side.Frosted Finish - A surface treatment for glass, consisting of an acid etching of one or both surfaces that diffuses transmitted light and reduces glare.Gas-Filled Units - Insulating glass units with a gas other than air in the air space to decrease the unit’s thermal conductivity (U-value) or to increase the unit’s sound insulating value.Gaskets - Pre-formed shapes, such as strips, grommets, etc., of rubber or rubber-like composition, used to fill and seal a joint or opening either alone or in conjunction with a supplemental application of a sealant.Girth - In bent glass, the distance around the concave or convex surface measured perpendicular to the height, including any flats.Glass - A hard brittle substance, usually transparent, made by fusing silicates, under high temperatures, with soda, lime, etc. Glass Clad Polycarbonate (GCP) - One or more lites of flat glass bonded with an aliphatic urethane interlayer to one or more sheets of extruded polycarbonate in a pressure/temperatuer/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 - (n) A generic term used to describe an infill material such as glass. (v) The process of installing an infill material into a prepared opening in windows, door panels, partitions, etc. Glazing Bead - A strip surrounding the edge of the glass in a window or door, which holds the glass in place.Glazing Channel - A three-sided, U-shaped sash detail into which a glass product is installed and retained. Ground Edge - A special fabrication done to the edge of a piece of glass. Makes the edge smooth and gives it a whitish/gray appearance. Gun Consistency - Sealant formulated in a degree of viscosity suitable for application through the nozzle of a caulking gun.Heat-Absorbing Glass - Glass that absorbs an appreciable amount of solar energy.Heat Resisting Glass - Glass able to withstand high thermal shock, generally because of a low coefficient of expansion.Heat Soak - A process of heating glass to a specific temperature for a specified time in a special oven in an attempt to find any impurities in the glass known as "nickel sulfide inclusions".

Heat Strengthened Glass (HS) - 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 Transfer Methods - Heat transfers from one place to another via convection, conduction or radiation. Convection occurs from the upward movement of warm, light air currents. Conduction occurs when energy passes from one object to another. Radiation occurs when heat is sent through space and is capable of traveling to a distant object where it can be reflected, absorbed or transmitted.

Heat Treated - Term used for both fully tempered glass and heat-strengthened glass. 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.High-Transmission Glass - Glass, which transmits an exceptionally high percentage of visible light.

Hurricane / cyclic wind-resistant glass - Laminated glazing tested to one or more test protocols for high velocity hurricane winds and windborne debris. Infrared (IR) - IR is part of the solar spectrum, or sunlight, that is invisible to the human eye. It has a wavelength range of ~790-3000 nanometers and has a penetrating heat effect. Short-wave IR converts to heat when it is absorbed by an object.

Insulating Glass (IG) - Two glass components separated by an air spacer and hermetically sealed. Inherently, insulating glass increases a window's thermal performance. Insulating Laminated Glass - An insulating glass unit inwhich the exterior component is a monolithic glass ply and the interior component is a laminated glass . 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 - Refers to the plastic or vinyl in a laminated unit. Examples are PVB, SentryGlas Plus, Saflex HP, Vanceva Storm, etc.

Iridescence - Also called strain pattern or Q-lines. It is a pattern in heat treated glass not normally visible except under certain lighting conditions. It is especially visible with the use of a polarized lens. Iridescence is an inherent characteristic of heat treated glass. Jambs - The vertical frame members at the perimeter of the opening.Joint - The space or opening between two or more adjoining surfaces.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.Knocked Down (KD) - Fabricated framing components shipped loose for assembly at another location.Laminated Glass -Two or more pieces of glass bonded together by a piece of plastic/vinyl called polyvinyl butyral (PVB.) A minimum interlayer thickness of .030 (.76mm) meets the requirements of ANSI Z97.1 or CPSC 16 CFR 1201 safetly glazing standards.

Laminated Insulating Glass - An insulating glass unit in which the exterior component is a laminated glass and the interior component is a monolithic glass ply.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.

Light to Solar Gain Ratio (LSG) - The ratio is equal to the Visible Light Transmittance divided by the Solar Heat Gain Coefficient. The Department of Energy's Federal Technology Alert publication of the Federal Energy Management Program (FEMP) views and LSG of 1.25 or greater to be Green Glazing/Spectrally Selective Glazing.Lehr - A long, tunnel-shaped oven for annealing glass, usually by a continuous process. Lite -Another term for a pane of glass. Sometimes spelled "light" in industry literature.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.

Low-E -An abbreviation for Low Emissivity coatings. They are applied to glass to reflect invisible long-wave infrared or heat. They reduce heat gain or loss in a building by redirecting the heat. In addition, they typically provide greater light transmission, low reflection and reduce heat transfer.

Lucor -A powder used to separate lites of glass to prevent damage from scratching or rubbing. Luminous Efficacy (Light-to-Solar Gain Ratio) - The visible transmittance of a glazing system divided by the solar heat gain coefficient (or shading coefficient). This ratio is helpful in selecting glazing products for different climates in terms of those that transmit more heat than light and those that transmit more light than heat.Mastic - Descriptive of heavy-consistency compounds that may remain adhesive and pliable with age.Mock-Up - A full size sample or model of a unit normally used to judge appearance and performance. Modulus - Stress at a given strain. Also tensile strength at a given elongation.

Monolithic - Refers to a single lite of glass as a finished product.

Mullion - A vertical framing member separating fixed lites of glass, operating sash, or door openings. Multiple-Glazed Units - Insulating glass units with three or more lites of glass.Muntins - Horizontal or vertical bars that divide the sash frame into smaller lites of glass. Muntins are smaller in dimensions and weight than mullions. Negative Air - Refers to an insulating unit wherein the two lites of glass are closer together in the center of the unit than they are at the edge. This gives the unit the appearance of being "bowed in".

Nickel Sulfide - an inclusion in float glass that can cause spontaneous breakage in fully tempered glass. Offset - Either a laminated or insulating unit wherein the two edges don't match up.

OITC Rating - An abbreviatoin for Outside-Inside Transmission Class Rating. This rating is used to classify the performance of glazing in exterior applications. It is based on ASTM E-1332 Standard Classification for the Determination of Outdoor-Indoor Transmission Class. While STC rating is based on a "White' noise spectrum, this standard utilizes a source noise spectrum that combines Aircraft/Rail/Truck traffic and is weighted more to lower frequencies.

Opacifier Film - An adhesive film applied to glass for spandrel applications.Organic - Any compound which consists of carbon and hydrogen with a restricted number of other elements, such as oxygen, nitrogen, sulphur, phosphorous, chlorine, etc.

Patterned Glass - One type of rolled glass having a pattern impressed on one or both sides. Used extensively for light control, bath enclosures and decorative glazing. Sometimes called "rolled," "figured" or "obscure" glass.Permanent Set - The amount by which a material fails to return to its original dimensions after being deformed by an applied force or load.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 (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.Polariscope - A device for examining the degree of strain in a sample of glass. Polished Edge - A special fabrication done to the edge of a piece of glass. Makes the edge smooth and gives it an extremely shiny or polished appearance. Polished Wired Glass - Wired glass that has been ground and polished on both surfaces.

Polycarbonate - Extruded plastic sheet that can be glazed singly or as a component of a laminated glazing product.

Polyisobutylene (PIB) - The primary seal of an insulating unit and the key component in restricting moisture vapor transmission. Polymer - A chemical structure consisting of long chains of molecular units.Polysulfide Sealant - Polysulfide liquid polymer sealant, which are mercaptan terminated, long chain aliphatic polymers containing disulfide linkages. They can be converted to rubbers at room temperature without shrinkage upon addition of a curing agent.

Polyurethane - Also commonly called urethane. Used by some insulating fabricators for a secondary sealant. It is also an interlayer used in polycarbonate security products. Polyurethane Sealant - An organic compound formed by the reaction of a glycol with an isocyanate.

Polyvinyl Butyral (PVB) - The plastic or vinyl used in the makeup of a laminated unit, the vinyl is what holds that unit together. Polyvinyl Chloride (PVC) - Polymer formed by polymerization of vinyl chloride monomer. Sometimes called vinyl.Pot Life - The time interval following the addition of an accelerator before a chemically curing material will become too viscous to apply satisfactorily. Positive Air - The opposite of negative air. In an insulating unit, where the center of the unit is farther apart than around the air spacer, these units have a bowed out appearance. Pre-Shimmed Tape Sealant - A sealant having a pre-formed shape containing solids or discrete particles that limit its deformation under compression.Primer - A coating specifically designed to enhance the adhesion of sealant systems to certain surfaces, to form a barrier to prevent migration of components, or to seal a porous substrate.Priming - Sealing of a porous surface so that compound will not stain, lose elasticity, shrink excessively, etc., because of loss of oil or vehicle into the surround. A sealant primer or surface conditioner may be used to promote adhesion of a curing type sealant to certain surfaces. Pyrolytic Deposition - A process of applying a thin metallic coating to the surface of flat glass during the float glass manufacturing process. R-Value - Thermal resistance is expressed in ft^2/hr/°F/BTU. It is the reciprocal of U-value. The higher the R-value, the less heat is transmitted through the glazing material. 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. RAT Equation - The RAT equation accounts for 100 percent of solar energy, which is equal to the sum of solar reflectance, absorption and transmittance. For example, with a single pane of 1/8" (3mm) clear glass, 83 percent of solar energy is transmitted, 8 percent is reflected and 9 percent is absorbed by the glass. Of the solar energy absorbed, portions are emitted back towards the exterior and towards the building interior.

Reflective Glass - Glass with a metallic coating to reduce solar heat gain.

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.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.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 that are 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 (also 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 - Glass formed by rolling, including patterned and wired glass.

Roller Wave - The appearance of waviness sometimes seen in heat treated glass caused by the glass moving over rollers in the tempering furnace. Rough Opening - The opening in a wall into which a door or window is to be installed.Rub - A series of small scratches in glass generally caused during transport by a chip lodged between two lites.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.

Sandblasted Finish - A surface treatment for flat glass obtained by spraying the glass with hard particles to roughen the surface. The method restricts vision while maintaining a level of light transmission. Sash - The window frame, including muntin bars if used, to receive the glazing infill.Score - To penetrate the surface of a lite of glass by means of a cutting device, e.g. a glass cutter, along a predetermined line in order to produce a lite of glass of a specific size and/or shape.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 (or Applied Stop) - Stop, molding or bead fastened by screws as compared with those that snap into position without additional fastening.Sealant - An elastomeric material with adhesive qualities, applied between components of a similar or dissimilar nature to provide an effective barrier against the passage of the elements.Seam (verb) - 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" (.8 mm) in diameter. SentryGlas® Plus (SGP) - A laminate that incorporates an ionoplast interlayer which is bonded directly between two layers of glass. The product was originally marketed for hurricane protection but is also used for blast mitigating applications. Setting - Placement of lites or panels in sash or frames. Also action of a compound as it becomes more firm after application.

Setting Blocks - Small pieces of neoprene or other material which are placed under the lower edge of a lite of glass to support it within a frame.

Shading Coefficient - Shading coefficient is the ratio of solar heat gain through a specific type of glass that is relative to the solar heat gain through a 1/8" (3mm) ply of clear glass under identical conditions. As the shading coefficient number decreases, heat gain is reduced, which means a better performing product. Shadowgraph - A device for inspecting glass with respect to distortion and other defects.Shelf Life - Used in the glazing and sealant business to refer to the length of time a product may be stored before beginning to lose its effectiveness. Manufacturers usually state the shelf life and the necessary storage conditions on the package.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).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. Silkscreen - A process of applying a specific design or pattern to glass. The design is made by placing a screen over a piece of glass and then pressing ceramic frit, by means of a large squeegee, through the pores of the screen. After the frit is applied, the glass goes through an infra-red oven to dry the frit and then through a tempering furnace to fire (bond) the frit to the glass permanently.

Skylight - A window glazed in a roof or ceiling of a building.

Sloped Glazing - Glass units that are glazed more than 15° off vertical.

Solar Control Glass - Tinted and/or coated glass that reduces the amount of solar heat gain transmitted through a glazing product. Smoke - Streaked areas appearing as slight discoloration on glass.Solar Control Glass - Tinted and/or coated glass that reduces the amount of solar heat gain transmitted through a glazed product.

Solar Energy - The sum total of the solar spectrum. 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 Heat Gain Coefficient (SHGC) - The portion of directly transmitted and absorbed solar energy that enters into the building's interior. The higher the SHGC, the higher the heat gain.

Solar Reflectance - The percentage of solar energy that is reflected from the glass surface(s)

Solar Reflective Coatings - Coatings that reduce heat gain through higher solar reflection.

Solar Spectrum - The solar spectrum, commonly referred to as sunlight, consists of ultraviolet light, (UV), visible light and infrared (IR). The energy distribution within the solar spectrum is approximately 2 percent UV, 47 percent visible light and 51 percent IR. One aspect of the solar spectrum is its wavelength in which nanometer (nm) is the unit of length [1 nm+10^-9 m].

Solar Transmittance - The percentage of ultraviolet, visible and near infrared energy (300 - 3000 nanometers) that is transmitted through the glass.Solarization - Change in transmission, and sometimes color, of plastics as a result of exposure to sunlight or other radiation.

Spacers (Shims) - Small blocks of neoprene, EPDM, silicone or other suitable material, placed on each side of the glass product to provide glass centering, maintain uniform width of sealant bead and prevent excessive sealant distortion. Spandrel - The panel(s) of a wall located between vision areas of windows, which conceal structural columns floors and shear walls. Glass panels incorporate either a ceramic frit, opacifier film, or are installed into a shadow box application. Spectrally Selective Glass - Tinted and/or coated flat glass that reduces the amount of solar heat gain transmitted through a glazed product. STC (Sound Transmission Class) - A single number rating derived from individual transmission losses at specified test frequencies (for more information see ASTM E 90 and ASTM E 413). It is used for interior walls, ceilings and floors and in the past was also used for preliminary comparison of the performance of various glazing materials.STL (Sound Transmission Loss) - 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)." STC Rating - Abbreviation for Sound Transmission Class Rating. When glass is used on the building interior, the sound transmission classification (STC) value can be used to categorize the glass performance. The STC rating is a single-number rating system for interior building partitions and viewing windows. The STC rating is derived by testing in accordance with ASTM E90, 'Laboratory Measurement of Airborne sound Transmission of Building Partitions". The STC value is achieved by applying the Transmission loss (TL) values to the STC reference contour of ASTM E413, "Determination of Sound Transmission Class". The STC rating is a basis for glass selection. Its original intent was to quantify interiro building partitions, not exterior wall components. As a result, it is not recommended for glass selection of exterior wall applications, since the single-number rating was achieved under a specific set of laboratory conditions. Stones - Any crystalline inclusion imbedded in the glass.Stop - Either the stationary lip or the removable molding of the rabbet, serving to hold the glazing infill in the sash or frame, with the help of spacers.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.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.

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.Striking Off - The operation of smoothing off excess compound or sealant at sight line when applying same around lites or panels.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 trnsfer of loads from the glass to its perimeter support system and retention of the glass in the opening.

Substrate - The raw glass or base material to which other materials or fabrication procedures are applied.

Tape Sealant - A sealant having a pre-formed shape, and intended to be used in a joint under compression.Thermal Endurance - The relative ability of glass to withstand thermal shock.Tin Side - The bottom side of float glass as it was manufactured. Called "tin side" because float glass rides on a bath of liquid tin while it is being cooled. Tinted Glass - Glass with colorants added to the basic glass batch that give the glass color, as well as, light and heat-reducing capabilities. The color extends throughout the thickness of the glass. Typical colors include bronze, gray, dark gray, aquamarine, green, deep green, blue and black.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 operation of pressing in and striking a sealant in a joint, to press the sealant against the sides of a joint and secure good adhesion; the finishing off of the surface of a sealant in a joint so that it is flush with the surface.Toughened Glass - International terminology for fully tempered glass. (See Fully Tempered Glass)Transmittance - The ability of the glass to pass light and/or heat, usually expressed in percentages (visible transmittance, thermal transmittance, etc.).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.U-Value - A measure of heat gain or heat loss through glass due to the differences between indoor and outdoor temperatures. These are center pane values based on NFRC standard winter nighttime and summer daytime conditions. U-values are given in BTU/hr/ft^2/°F for the English system. Metric U-values are given in W/m^2/°C. NFRC winter nighttime U-values are based on an outdoor temperature of 0°F (-17.8°C), an indoor temperature of 70°F (21°C) and a 12.3 mph (19.8 km/h) outdoor air velocity. NFRC summer daytime U-values are based on an outdoor temperature of 89°F (32°C), an indoor temperature of 75°F (24°C), a 6.2 mph (10.1 km/h) outdoor air velocity and a solar intensity of 248 BTU/hr/ft^2/°F (782 W/m^2).

Ultraviolet Light (UV) - The name of the invisible portion of the light spectrum with wavelengths shorter than 390 nanometers. The damaging effects on long-term UV exposure results in fabric fading and plastic deterioration.

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.Vacuum (Sputtering) Deposition - Process for applying multiple layers of metallic coatings to the surface of flast glass in a vacuum chamber.

Vinyl Glazing - Holding glass in place with extruded vinyl channel or roll-in type.Visible Light Reflectance - The percentage of visible light (390 to 770 nanometers) within the solar spectrum that is reflected from the glass surface. Visible Light Transmittance - The percentage of visible light (380 - 780 nanometers) that is transmitted through the glass. (Visible light is the only portion of the solar spectrum visible to the human eye.) 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 (also Stain) - Attack of a glass surface by atmospheric elements.Weather-stripping - A material or device used to seal the opening between sash and/or sash and frame.Weeps (or Weep Holes) - Drain holes or slots in the sash or framing member to prevent accumulation of condensation and water.Wet Seal - Application of an elastomeric sealant between the glass and sash to form a weather-tight seal.Window - An opening constructed in a wall or roof and functioning to admit light or air to an enclosure, usually framed and spanned with glass mounted to permit opening and closing. Wired Glass - Rolled glass having a layer of meshed or stranded wire completely imbedded as nearly as possible to the center of thickness of the lite. This glass is available as polished glass (one or both surfaces) and patterned glass. Approved polished wired glass is used as transparent or translucent fire protection rated glazing. Patterned wired glass is sometimes used as decorative glass. It breaks more easily than unwired glass of the same thickness, but the wire restrains the fragments from falling out of the frame when broken.Work Life - The time during which a curing sealant (usually two compounds) remains suitable for use after being mixed with a catalyst.Zebra Board - A board with alternating black and white diagonal lines used to observe optical transmission and reflection qualities in coated and uncoated glass.