Glossary » Viridian Glass


Or the Glassary as we like to call it – where we set the record straight on all the technical stuff. Search from hundreds of industry terms to find the explanation you’ve been looking for.



A wearing, grinding or rubbing away by friction.

Abrasion Resistance

The inherent ability of a coating or substrate to resist degradation or destruction by friction.


That portion of total incident radiation that is absorbed by the glass and subsequently re-radiated either outside or inside.

Acid Etching

The process of decorating glass, which involves the application of hydrofluoric acid to the glass surface.


Sharpness of image.


– Australian Fenestration Rating Council – the Australian body which manages the performance ratings of various glass types.


– Australian Glass & Window Association – The peak association representing companies covering window manufacturers, glass manufacturers, glass processors, merchants, glaziers and suppliers of supporting machinery, services and materials.


The space in the cavity between two glass panes in an insulated glass unit.

Ambient Temperature

The surrounding temperature existing at any given time.

Annealed Glass

Glass cooled gradually during manufacture in an annealing operation to reduce residual stresses and strains that can occur during cooling. Technically, the stress condition of ordinary glass which is glass that can be cut and processed. This is the normal cuttable glass that is generally available.


In the manufacturing of float glass and obscure 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 on-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 inherent in the flat glass product to allow normal cold end cutting and processing.

Annealing Point

Temperature at which the viscosity of the glass is approximately 1013 Poises. At the annealing point of glass, internal stresses are substantially relieved in a matter of minutes.

Anti Bandit Glazing

A type of security glazing, typically laminated glass, designed to resist manual attack and to delay access to the protected space for a short period of time.

Antique Glass

Glass with an uneven surface texture and bubbles inside, produced by using antique methods in order to obtain the appearance of glass made before the development of industrial processes.

Application Life

Period of time during which a sealant can be effectively applied to a joint. The timing is from completion of mixing and could be affected by temperature, humidity or a combination of both. Also known as Working life.


Recommended places to use this type of glass


An inert, non-toxic gas placed between glass panes in an insulated glass unit in order to improve the insulating properties of the unit.


A small bevel at an angle of approximately 45 degrees to the edge points of the glass, applied usually with a wet or dry belt, stone or machine.

Arrised Edge

The result of removing sharp edges.

Aspect Ratio

The ratio of the longer side of a panel to its shorter side.

Asymmetrical Material

Material is asymmetric when it is composite and some of the components are of different thicknesses.


The reduction of sound intensity (or signal strength) with distance. Attenuation is the opposite of amplification, and is measured in decibels.


A now superseded trade name for the Viridian range of tinted float glass. Now known as VFloat.


A pressure tank vessel that employs high pressure and heat to produce bonding between glass and PVB or urethane sheet, creating a PVB laminated glass product.



Clearance Space between the surface of the glass and the back of the rebate.

Back Putty

That portion of the compound remaining between the back of the rebate and glass after the glass has been pressed into position in the bedding putty.

Backing 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 hourglass contour of the finished sealant bead.


A vertical member supporting a handrail and forming part of a balustrade.


A framed or unframed barrier between handrail and floor level (see also handrail).


A surface defect that looks like hammered metal. Unless very heavy, it usually cannot be seen by the naked eye, although it can be clearly seen on the shadowgraph.


A strip of timber, aluminium or other suitable material secured to the rebate to retain the glass in place (sometimes referred to as a glazing bead).

Bed or Bedding

The glazing material used to seal between the glass and frame/bead.

Bedding or Stop

In glazing, the application of compound at the base of the channel, just before the stop is placed in position, or buttered (see Buttering) on the inside face of the stop.


The process of manufacturing bent glass.

Bent Glass

Glass produced by heating annealed glass to the point where it softens and which then can be pressed or sag-bent over formers. Bends can be created in one or two planes. Bending can be incorporated in the toughening process. Bent glass can also be laminated.


A sloping edge on a glass sheet commonly used on mirror glass.

Bevel Both Sides

The edges to both surface sides of the glass are bevelled to the usual standard bevel.

Bevel To Butt

The process of producing a small mitre bevel to butt edges typically on mirrors.


The process of grinding and polishing a sloped angle on the face of the edge of flat glass which results in a decorative edge appearance to the glass.


Also referred to as structural bite, is the width of silicone sealant that is applied to the panel of glass to adhere it to the frame.


Migration of colour from the coating film onto or into a surface with which it comes in contact.


A noticeable imperfection in or on the surface of the glass.


An elongated bubble larger than seed.


A profusion of bubbles or gaseous inclusions in glass. Small bubbles less than 2mm diameter are referred to as seeds.


A small piece of lead, wood, santoprene or rubber or other suitable material used to position glass in a frame. Refer setting blocks.


A surface film on glass resulting from atmospheric attack or deposition by smoke or other vapours.

Blow in

A separation of glass and interlayer at or close to the edge of laminated glass caused by penetration of the autoclaving medium into the edge during laminating.

Body Tinted Glass

Glass produced by the addition of metal oxides to the molten glass which do not materially affect the basic properties except for the colour and solar energy transmission.


A curve, bend or other deviation from flatness in glass.

Break Pattern

The resultant pattern formed by the cracks within an individual pane of glass when broken.

Breather Tube Units

An insulating glass unit with a tube factory-placed into the unit’s spacer to accommodate pressure differences for units being installed at high altitudes. These tubes must be sealed on the job site prior to unit installation.

Brewsters Fringes

A rainbow effect sometimes seen in double glazing caused by the light refraction from identical thicknesses of glass.

Brilliant Cut

Decorative process in which designs are cut into glass with abrasive and polishing wheels.

British Thermal Units BTUs

The amount of energy (in imperial units) needed to raise one pound of water from 63°F to 64°F.

Bronze Glass

See tinted glass.


In float glass and obscure glass, a gaseous inclusion. In laminated glass, a gas pocket in the interlayer material or between the glass and the interlayer. Also called a blister or seed.

Bulb Edge

In float glass manufacture, the extreme lateral edge of the ribbon as floated down the line.

Bull Nose

The rounding, in the form of a quarter circle, of half of the cut edge of the glass. The remaining surface edge is slightly rounded. Also known as half round.

Bullet Resistant Glass

A multiple lamination of glass and plastic that is designed to resist penetration from medium-to-super-power small arms and high-power rifles.


A glass panel having a formed antique style circle in its centre for decorative effect. Originally the cut-out bottom of a mouth blown glass cylinder.

Butt Glazing

The installation of glass products where the vertical glass edges are glazed with silicone and without structural supporting mullions.


Application of sealant or compound to the flat surface of some member before placing the member in position; for example, the buttering of a removable stop before fastening the stop in place.



Abbreviation for cut-to-size glass.


Processing Computer Aided Design, the use of a computer to produce graphics.


The amount of energy needed to raise one gram of water from 14.5°C to 15.5°C.

Cantilevered Balustrade

The use of glass in a balustrade where it forms a structural enclosure or barrier. The glass is installed or cement fixed directly into channels or with fixings and the glass takes all loads directly back to its fixing point.

Capillary Tube Units

An insulating glass unit with a very small metal tube of specific length and inside diameter, factory-placed into the unit’s spacer to accommodate pressure differences encountered in shipping to high altitudes. (See also Breather Tubes).

Casement Window

A window, pivoted or opening on side hinges.

Cast Glass

Glass produced by ‘casting’, in other words by pouring molten glass into a mould or by heating glass in a tank and extruding it through patterned rollers.

Cast-In-Place Lamination (CIP)

Lamination process where the interlayer is obtained by pouring a liquid between plies of glass or plastics glazing sheet material, which is then cured to produce the final product.

Central Area of Sheet

The area that forms an oval or circle centred on the sheet, whose axis or diameter does not exceed 80% of the overall dimension. This allows a fairly large area at the corners, which may have imperfections that are not allowed in the central area.

Centre Tension

Residual tension stresses within the centre (core or zone) between the surface compression layers of thermally toughened and heat-strengthened glass.

Ceramic Enamel

A combination of crushed glass, metal oxide colourants and flux mixed in an oil or water medium and fused onto glass. Also known as ceramic ink.

Cerium Oxide

The oxide of the rare earth group, used alone or together with other substances as a polishing agent for glass.

Chair Rail

A fixed glazing bar or rigid push bar that provides protection from human impact. Also known as a crash rail.

Channel Depth

The measurement from the sight line of the frame to the bottom of the channel.

Channel Glazing

A three-sided, U-shaped opening in sash or frame to receive light or panel. Also known as perimeter channel.

Channel Width

The distance between the fixed and removable beads at the widest point.


Very small cracks in flat glass, usually at the edge. Though small, these are cause for concern since they can be intensified under strain (See Edge Vents).

Chemical Durability

The lasting quality, both physical and chemical, of a glass surface. It is frequency evaluated after prolonged weathering or storage, in terms of physical and chemical changes in the glass surface (see Weathering).

Chemically Toughened Glass

Chemical strengthening of glass is brought about through a process known as ion-exchange. Glass is submersed in a molten salt bath at temperatures below the annealing range of the glass. In the case of soda lime silica glass, the salt bath consists of potassium-nitrate. During the submersion cycle, the larger alkali potassium icons exchange places with the smaller alkali sodium ions in the surface of the glass. The larger alkali potassium ions ‘wedge’ their way into the voids in the surface created by the vacating smaller alkali sodium ions. This ‘strengthened’ surface may penetrate to a depth of only a few microns. It is not a recognised safety glass.


A small shallow piece of glass which has become detached from the original glass edge or face or the void it has left.

Chipped Edge

An imperfection due to the breaking of a small fragment from the cut edge of the glass. Generally this is not serious except in heat absorbing glass.


A straight line (or measurement), joining ends of an arc.

CIP (Cast In Place)

Lamination process where the interlayer is a liquid poured between two plies of glass and then chemically or UV cured to produce the final laminated glass product.

Cladding Glass

Toughened or Heat strengthened glass usually painted or silk-screened using ceramic ink as a colouring agent for use in curtain walls or as a cover to columns and walls. (See also Spandrel).

Clear Glass

Architectural clear glass is almost invariably of the soda-lime-silica type. Composition varies with manufacturer but is generally silica (SiO2) 70% to 74%, lime (CaO) 5% to 12% and soda (Na2O) 12% to 16%, with small amounts of magnesium, aluminium, iron and other elements.

CNC Processing

Computer Numeric Control. This type of machinery enables the processing of sophisticated shapes and hole contours in glass.

Cohesive Failure

Internal splitting of a sealant resulting from over stressing and insufficient elasticity and elongation to absorb the strain.

Coincidence Dip

The frequency at which a glass panel vibrates in unison with the frequency of the incident sound pressure waves thus significantly reducing the sound insulating properties of the glass at that specific frequency.

Colonial Bars

Horizontal or vertical bars that divide a sash frame into smaller panels of glass. Colonial bars are smaller in dimensions and weight than mullions. They are sometimes surface fixed to glass.

Colour co-ordinated

A system that can be used to assign numbers to specify or describe the colour of glass or the colour of coating on glass.

Colour Tone Pattern Available

Colours often refer to coloured interlayers or seraphic screen printing, tones refer to the colouring of the glass material and patterns often refer to patterns that are rolled onto the glass during production or by seraphic screen printing

Colour Variation

Noticeable colour differences between glass panels, or within one panel of glass or coated glass.


Pressure exerted on the glazing compound sealant, tape or gasket by the glazing method.


The appearance of moisture (water vapour) on the surface of glass caused by warm moist air coming into contact with the colder surface of the glass.


Heat transfer in which there is a direct contact of molecules in a solid body, e.g. the passage of heat along a metal bar of which one end is inserted into a fire.


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, and the like.


Heat transfer in which actual movement of the medium, gas or liquid occurs e.g. heated air from a convection heater.

Coolness Factor

(See Luminous Efficacy).


Attenuated glassy inclusions that possess optical and other properties differing from those of the surrounding glass. Cords are the result of non-homogeneity. Low intensity cords are called strings, wire lines or ream.

Corners On/Off

Section of glass remaining on or removed from the corner of a sheet, caused by the score mark not continuing right through to the traverse mark.

Countersunk Hole

A hole which has been ground out at the surface to receive a mechanical fixing, allowing the bolting or fixing of the glass panel.

Covered Edge

The perimetric area of the glass covered by the channel or sash when installed. Also known as edge cover.

Crash Rail

A rail, together with its fixings, capable of withstanding a load of 750N per metre length, acting in any direction without contact with the glazing material.


Broken glass , the excess glass from previous glass manufacture or edge trims off the cutting of glass to size. Cullet is an essential ingredient in the pre-melt raw glass mix as it facilitates the melting process.

Curing Agent

One part of a two-part sealant, which, when added to the base, will cause the base to change its physical state by chemical reaction between the two parts.

Curtain Wall

A non load-bearing wall of metal sections, glass and infill panels, which is carried directly by the structure of a building. Extensively used in modern high-rise office buildings.

Cut sizes

Any flat glass cut to specific dimensions. Also known as cut-to-size


The removal of a section of a glass panel.


(a) A person who cuts glass. (b) The tool used in cutting glass.


Scoring glass with a diamond, steel or hard alloy wheel and breaking along the score.


Damage Weighted

The measurement of the relative fading reduction over the whole solar spectrum, not just ultra violet. It is weighted to address the fact that fading results from a broad band of solar energy.

Daylight Size

The clear height and width between frame members that admits light.


A specially prepared paper on which designs have been printed for the purpose of transferring to glass.


The process of producing a colourless appearance in glass.

Decorated glass

Clear or patterned glass processed by craftsmen for decorative effect. Stained glass, leadlights and sand-blasted, acid-etched, embossed and printed glass fall into this category. Decorative interlayers can also be incorporated in laminated glass.


(a) Firing enamels onto glassware. (b) Applying designs to formed glassware by means of etching, sandblasting, cutting, engraving or similar methods.

Deflection (centre of glass)

The amount of bending movement of the centre of a glass panel, perpendicular to the plane of the glass surface under load (usually wind load).


A condition in which one or more of the glass plies of laminated glass loses the bond with the interlayer. Often it is a minor edge discolouration reaction from sealant.

Desiccant (Silica Gel)

Molecular sieve or extremely porous crystalline substance used to absorb moisture inside the air space of insulated glass units.

Design Wind Pressure

The specified pressure a product is designed to withstand.


Crystallization in glass.

Dew Point

The temperature at which condensation of moisture begins when air is cooled.


The more or less cubicle (cubic?) pattern of fracture of fully tempered glass, the edges of the dice being roughly equal to the thickness of the glass (see break pattern).

Dichroic Coatings

Multi-layered coatings that exhibit different colours by reflection and transmission as a function of viewing angle.

Dielectric Coating

A flexible, electrically insulating coating suitable for application by spraying, dipping and syringe dispensing. NOTE: The range of performance available from the use of metallic coatings is limited because of the thickness of coating that has to be applied. The use of dielectric coatings, which produce interference effects, allows higher light transmission with increased selectivity; the range of colours is also increased.

Dielectric Constant

The ratio of the electric energy of the field set up in a dielectric material to that set up in a vacuum. At a given frequency, it is the ratio of the capacitance of the capacitor with the glass material as the dielectric to the capacitance of the same capacitor with a vacuum as the dielectric.

Diffuse Reflection

Glass used in picture framing to avoid reflections and the glare of lighting.


Scattering, dispersing, as the tendency to eliminate a direct beam of light.


Deep, short scratches.

Diminishing Stop Bevel

A bevel in which only a portion of the surface edges is bevelled, the bevel running out on a small radius.

Direct Transmittance

That portion of the sun’s emitted solar heat energy which is directly transmitted through the glazing.

Distance Piece (Shims)

Small blocks of resilient, non-absorbent material (such as extruded rubber) used to prevent the displacement of glazing compound or sealant by external loading. They are positioned opposite each other between the glass and rebate, and glass and bead.


Alteration of viewed images caused by variations in glass flatness and is an inherent characteristic of glass that has been heat treated.

Double Bevel

The surface edge of the glass on the face that is bevelled, the bevel consisting of two intersecting planes.

Double Glazing

In general, any use of two panels of glass, separated by an air space, within an opening to improve insulation against heat transfer and/or sound transmittance. 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

Draw Lines

Refers to the direction of flow (or pull) of the glass during production of sheet glass. Float glass has eliminated this issue.

Drop Height

The vertical distance used from the horizontal centre-line of the maximum diameter of the impacting object when it is released, relative to the horizontal centre-line of the impacting object when it is at rest.

Dry Glazing

Also called compression glazing. This term is used to describe the glazing or sealing in of single glass or insulating glass in the supporting framing system without wet sealants using pre-formed and extruded materials such as glazing gaskets and wedges.

Dry Seal

A weather seal between the glass and frame using foam tapes or gasket materials. Note: A dry seal may not be completely watertight.

Dual Seal

Insulating Glass units manufactured with a primary seal and a secondary seal for maximum protection against moisture vapour transmission.


An instrument for measuring the relative hardness of materials such as rubber. Also, the term often used (loosely) as a synonym for relative hardness.


Edge Blocks

Rubber blocks that prevent glass from moving sideways in the glazing rebate from thermal effects or vibration.

Edge Compression

The compression stresses (similar to surface compression) measured at the very edge of a heat-treated light of glass. The values of compressive stresses may vary on each edge of a given light.

Edge Cover

The distance between the edge of the glass and the edge of the rebate forming the sight opening of the window frame.

Edge Defects

Glass defects that include vents, shells, flakes, chips, wave, shark’s teeth, nibs, corners on/off.

Edge Vent

Cracks that run in from the edge of the glass.

Edge Work

Grinding, smoothing, bevelling or polishing the edge of flat or shaped glass.


The ‘painting’ or ‘cladding’ of the perimeter edge of glass panels prior to toughening which results in a fused colour to the edge for protection of sealants and adhesives against UV degrading.


Being of an elastic, rubber-like substance, such as natural or synthetic rubber.


The ability of a material to emit radiant energy. Emittance is the ratio of the total radiant energy emitted by a given surface to that emitted by an ideal black body at the same temperature. To emit is to give out, to discharge. In the case of glass, essentially, to re-radiate absorbed energy (heat).


Abrading the surface of the glass to achieve decorative designs by means of copper wheels, diamond points, carborundum pencils and other flexible drive tools. The engraving can consist of ‘brilliant’ cutting of various geometric shapes in the glass surface, which can be further polished.

Environmental Control Glass

A broad name for all types of glass that have a function in controlling noise, heat, glare or radiation (see also Solar Control).


To alter the surface of glass with hydrofluoric acid or other caustic agents.

Exposed Edge

A glass edge that is not covered. NOTE: Glass with exposed edges has no protection from damage, and may cause injury to those who come in contact with it.

Exterior Glazed

Glass inserted from the exterior of the building.

Exterior Stop

The removable moulding or bead that holds the glass in place when it is on the exterior side of the glass, as contrasted to an interior stop located on the interior side of the glass.

External glazing

Glazing, either side of, which is exposed outside the building.



The whole exterior of the side of a building that can be seen in one view – generally the front.

Face Mitre

The application of a machined mitred edge to the front surface of a pane of glass, which will result in the butting pane aligning to the face of the glazing.

Faceted Glazing

Glazing with vertical strips of glass (facets) joined at the vertical edges with silicone joints to typically form a radius window


Faults and imperfections, which include the following: (a) Bubble (b) Blemish (c) Bloom (d) Seed (e) Chip (f) Feather

Feather Edge

Any bevelled edge where the bevel is brought as close as practicable to the back edge of the glass.


Any glass panel, window, door, curtain wall or skylight unit on the exterior walls providing joinery to the building.


Poorly annealed glass that results in poor cutting from residual tension or bowing.

Figured Glass

Glass that is generally produced by the rolled process (see ‘rolled glass’). The surface of the rollers used carry the pattern or design to be ‘imprinted’ in the glass as it passes between them. The process gives the glass a textured surface on one or both sides. The surface finish may be both decorative and functional. Apart from the huge variety of patterns possible, figured glass can also offer light dispersion and glare reduction characteristics. Also known as ‘patterned’ or ‘obscure glass’.

Finger Slots

The slot produced by processing the surface of the glass by grinding in a slot for use as a finger grip in sliding the glass panels.

Finished Size

The finished size of the glass after cutting and processing is complete.


Supporting glass panels, usually vertical, located at a 90° to the glazed surface, usually behind a butt joint.

Fire Cracks

Small cracks penetrating the surface of the glass usually in the shape of short hooked crescents.

Fire-Rated Glass

Glass that resists the penetration of flames and/or smoke for a period of time, in accordance with appropriate Standards.


Laminated Glass Laminated glass containing an interlayer that reacts to high temperature to give the product its fire resistance. This product may also contain glass components that are themselves fire resistant.


A process to produce permanent colours on glass by firing ceramic colour onto the glass surface at high temperature (600°C).


Defect in coating film, generally a circular depression, usually resulting from contamination of the substrate surface; the coating flows away from the contaminant.


Any item that is used to secure – (a) members of a window assembly to each other; (b) an item of hardware to a window member; (c) a completed window assembly into the building structure.

Fixing Compound

A material used in fixing glass, applied by hand, knife or trowel, or as a pre-formed strip, and capable of adhering to a wide variety of surfaces.


Bevel-like protrusion above the cut edge, but different from a corner-on in that it often has a razor sharp edge.


A protrusion on the edge of a panel of a glass.


An impervious membrane or material which must be compatible with the framing materials and fitted in such a manner as to waterproof (the installation in-delete?) the building.

Flat Glass

A general term that describes construction float glass, sheet glass, plate glass and rolled glass.

Flat Ground Edge

Glass, the cut edges of which are machine ground flat and the surface edges are slightly arrised without a final polish.

Float Glass

A transparent glass, the two surfaces of which are flat, parallel and fire polished so that they give a clear undistorted vision and reflection. Float glass is manufactured by floating a ribbon of molten glass over a bath of liquid tin which has a greater density than that of glass.

Flush Glazing

Glass glazed to an aluminium frame without any external mullion or transom projections.


A unit of brightness equalling one lumen (the basic unit of light) per one square foot of a perfectly white, completely reflectant surface. Brightness in foot-lamberts = Illumination in lumens ´ (P? p?)ercentage of reflectance

Formed Glass

Glass that has been heat-treated to mould patterns or designs into the surface of glass. Also known as slump glass.

Fracture Pattern

The resultant pattern formed by the cracks within an individual light of glass when broken.


A structure manufactured from timber, metal, glass, or other durable material or combinations of materials, such as glass fins and structural sealant supporting the full length of all the edges of the glazed panel.


Raw materials mixed together and melted to form glass.

Front Clearance

The space between the face of the glass and the bead.

Front Putty

A triangular fillet of putty formed between the surface of the glass and the rebate platform, or that portion of compound remaining between the bead and the glass, on completion of glazing.

Frosted Finish

A surface treatment for glass, consisting of acid etching or sandblasting of one or both surfaces to diffuse transmitted light.


Fire Resistant Rating. The classification given to a glass type or glazing system to resist fire, relative to certain measurements.


A glass particle or crystalline material that is permanently bonded to a surface of a light or pane of glass.



The filling of the cavity of a sealed, insulating glass unit with a special gas to enhance the thermal insulation and/or acoustic properties.

Gaseous Inclusions

Round or elongated bubbles in the glass.


A pre-formed resilient rubber-like compound providing a continuous surround for glass and a weather tight seal when compressed.

Georgian Wired

Glass Incorporating wire mesh square pattern. The glass may be cast or clear polished.


A process employed largely for lettering and decorative work, whereby leaf metal such as gold leaf is applied to the glass surface and coated with a protective medium.


The measurement around the perimeter of a curve or bend.


The discomfort or impairment of vision, or both, caused by extreme contrasts in the field of vision, where parts such as lamps, the sky, the sun or reflecting surfaces are excessively bright in relation to the general brightness of surroundings.

Glass Block

A rectangular or square hollow block made of cast glass, and produced in a range of shapes for use in non-load-bearing partitions. Glass blocks are usually translucent, produce an even distribution of light, and are patterned on the interior or exterior face(s) to obscure through-vision.

Glass Brick

See Glass Block

Glass Clad Polycarbonate

Two or more panels of flat glass bonded with a urethane interlayer to one or more sheets of extruded polycarbonate in a pressure/ temperature/vacuum laminating process.

Glass Fin

A piece of glass positioned to provide lateral structural support to a glass wall.

Glass Flooring

Composite of three or more layers of annealed or toughened glass with highly tear resistant interlayers with a non-slip coating fused onto the upper surface.

Glass Stop

A small timber moulding or metal section for holding glass in place, usually rectangular, or with a rounded or bevelled edge (see Glazing Bead).

Glazier’s Putty

A stiff, dough-like material consisting of chalk whiting and linseed oil with white or other pigment. Used for setting window panes in timber sashes or filling (stopping) imperfections or crevices in other surfaces


1 The securing of glass in prepared openings in windows, door panels, partitions, and the like. 2 Glass or plastics glazing sheet material for installation into a building.

Glazing Bar

An aluminum extrusion typically used for glazing systems in roofs.

Glazing Bead

A small timber moulding or metal section for holding glass in place, usually rectangular, or with a rounded or bevelled edge. Also called ‘Glass Stop’.

Glazing Compound

A material used in glazing, applied by hand, gun, knife or trowel, to provide bedding for the glass and a weather-tight joint between the glass and frame.

Glazing Gasket

Plastic or synthetic rubber extrusion used between the glass and the frame or the glass and the bead.

Glazing Groove

A groove made to receive glass.

Glazing Panel Size

The actual size of the pane of glazing material.

Glazing Quality

In float glass, the standard glass supplied to buildings when quality is not otherwise definitely specified

Glazing Shoe

A mechanical fixing at the end of a sloped glazing bar to stop the glass panel sliding or protruding past the bar at the gutter or exposed end.

Glazing System

Any combination of glass and/or any other material that fills a window opening.

Glue Chip

Decorative glass produced by sticking material onto the glass with a glue. As the glue cures the material is stripped off the glass, the surface of which is plucked. This gives a random pattern.

Greenhouse Effect

The description applied to the phenomenon that keeps the planet warm. The earth’s atmosphere transmits short-wave solar energy, but then traps the absorbed solar heat that re-radiates in the form of long-wave infra-red radiation. It is a misconception that greenhouses become warm because of the greenhouse effect. The glass in an ordinary greenhouse acts as a convection trap rather than a radiation trap.



A horizontal or sloping rail(ing) at about waist height, which is grasped by the hand for support and which forms a safety rail to guard the side of a stairway, landing, elevated platform, walkway or bridge. Handrails form the top of the balustrade on open sides and are supported on handrail brackets on enclosed (wall) sides.

Hard Coat

Coating applied to glass during its manufacture whereby it is fused to the glass in the form of a pyrolitic coating. It is very durable and can be cut and toughened from stock.

Heat Absorbing Glass

Glass that absorbs amounts of solar energy (e.g. tinted glass).

Heat Gain and Heat Loss

Heat gain occurs in the summer months, when the exterior temperature is above the interior temperature and the heat flows inward. Heat loss occurs in the winter months, when the interior temperature is warmer than the exterior temperature and heat flows outward. Heat gain or heat loss are generally measured by U value.

Heat Soaking

Heat soaking is the process whereby toughened glass is reheated for a period of time at high temperatures to induce breakages that may be caused by inclusions or contaminants in the glass.

Heat Strengthened Glass

Flat or bent glass that has been heat treated to a specific surface and/or edge compression range. 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 fragment as will fully toughened glass

Heat Transfer

Heat is transferred in the following manner: Conduction – in which there is direct contact of molecules in a solid body, for example; the passage of heat along a metal bar of which one end is inserted in a fire. Convection – in which actual movement of the gas or air occurs; for example, heated air from a convection heater. Radiation – by which heat passes from source to object without heating the space between them; for example, heat from the sun to earth.

Heat Treated

Annealed glass heated to a temperature near its softening point and forced to cool rapidly under carefully controlled conditions. Heat-treated glass may be either heat strengthened or fully toughened (fully tempered).

Heat-Reflecting Glass

Surface-treated glass that reduces solar heat gain through reflection.

Heat-Resisting Glass

Glass with a low coefficient of expansion, which is therefore less liable to thermal shock. Borosilicate is the most common type of heat-resistant glass.

Heat-strengthened Laminated Safety Glass

Laminated safety glass utilizing two or more panels of heat strengthened glass in the make-up.

Heel Bead

Sealant applied at the base of a window channel, after setting the glass panel and before the bead is installed. One of its purposes is to prevent air and water penetration.

Hermetically sealed

Made airtight by fusion or sealing. Insulated Glass Units are hermetically sealed.

High light transmission glass

Transmits a high percentage of visible light. Also known as low iron glass.


A sash hinged at the bottom and often fitted with side checks to prevent cross draughts in a room.

Horticultural glass

Used for glass houses and other horticultural applications.

Hydrofluoric acid

A highly corrosive acid that attacks silicates such as glass. Pure Hydrofluoric acid dissolves glass, leaving a brilliant, acid-polished surface.



A crystalline or non-crystalline particle entrapped in glass.


That part of the solar spectrum that is invisible to the human eye (780 to 2500nm).

Insulating Glass Unit (IGU)

Two or more panes of glass spaced apart and factory sealed with dry air or special gases in the unit cavity. Often abbreviated to IGU or DGU and referred to as a unit.


Plastic material used between two or more glass panels in the manufacture of laminated safety glass to bond the glass together.

Intumescent Interlayer

A type of interlayer in fire-resistant laminated glass, which becomes opaque when exposed to fire.


A surface rainbow effect similar to an oil-on-water appearance. Normally caused by atmospheric moisture or alkali attack.

Irregular Shape

A shaped piece of glass that is not a straight edged rake and cannot be expressed as a size on paper without a diagram.



Vertical frame member at the perimeter of the opening of a window or door.


Keeps the heat in

Keeping you warmer in winter,controlling the flow of heat to reduce artifical heating

Keeps the heat out

Keeping you cooler in summer, it’s the capacity of the glass to direct heat back towards it’s source and away from the interiors of your home.


Laminated Glass.

A composite material consisting of two or more sheets of glass permanently bonded together by a plastic interlayer material. NOTE: Laminated glass will crack and break under sufficient impact, but the glass will tend to adhere to the plastic interlayer instead of falling apart.

Laminated safety glass

Laminated glass that satisfies the test requirements of the relevant safety glazing material Standards.

Lead Glass

A type of glass produced when lime in the batch is replaced by lead oxide for X ray shielding uses.


The specific width of the furnace or annealing ribbon which designates the sizes available from that float line. (See Annealing).

Lehr End Size (LES)

The standard dimension size produced by the width of a float line which usually comprises one constant specific size of the float produced.


A pane or sheet of glass.

Light Transmission

A term sometimes used to refer to the amount of visible light transmittance through a type of glass, usually expressed as a percentage.

Liquid-Pour Laminated Safety Glass

Two or more sheets of glass permanently bonded together by a liquid resin that cures to form a plastic-type interlayer, which meets the safety glazing requirements of the relevant safety glazing material Standards. Also known as CIP laminate.


See Light or Window Light

Live load

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


A window unit comprising a series of blades of glass or other material lapping over each other when in the close position.

Low Emissivity Glass (Low E)

Commonly known as ‘Low-E’ glass and often used in double and triple glazing units, this window glass has a special thin film of metallic oxide coating that 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 allows light to enter while also providing thermal insulation.

Low Iron Glass

Very low in iron content and consequently is extremely white and clear and transmits an exceptionally high percentage of visible light.

Low Reflection Coatings

Special coating on glass to reduce reflection and improve vision through the panel.

Luminous Efficacy (Light-to-Shading Coefficient Ratio)

The visible transmittance of a glazing system divided by the 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. Also referred to as the Coolness Factor.



Making glass visible. The marking of glass so as to minimise the potential for human impact and injury.


Heavy consistency compounds which may retain their adhesiveness and pliability with age.


Without lustre or gloss; dull.

Max Height

The maximum height that can be manufactured

Max Width

The maximum width that can be manufactured

Maximum Thickness

The thickness of a panel of glass at the maximum thickness tolerance.

Minimum thickness

The thickness of a panel of glass at the minimum thickness tolerance.


A piece of glass silvered on one side.

Mirror silvering

A chemical process depositing a coating of metal, mostly silver, onto the surface of clear glass. This deposit is usually protected by a layer of copper, which in turn is protected by a paint backing. The silver gives the mirror its reflective properties.


Misalignment of the edges of two lights of glass in laminated glass or in insulating glass units.

Mitre Bevel

Both Sides Bevelling of both surface edges of the glass and, unless otherwise specified, with a complete angle of approximately 68°.

Mitre bevel DDDD

The bevelling of the cut edge of the glass to an angle of approximately 45° (unless otherwise specified); the extreme point is slightly arrised. Also known as Mitre.

Modesty Panels

A panel of toughened shower screen glass silk-screened with a decorative pattern to give a discreet curtain effect.


Stress at a given strain. Modulus of elasticity is the tensile strength at a given elongation.

Monolithic Glass

A single light or piece of glass as opposed to laminated glass or an insulated glass unit.


A blotchy appearance in a coating film.


A vertical intermediate framing member. When used in curtain walls it represents all vertical members.


Laminated glass comprising three or more lights of glass.

Multi-Light Window

A window incorporating more than one opening or fixed light, or both, within one perimeter frame, as low lights, high lights or side lights. Multiple glazed units See Insulating Glass Units.



A synthetic rubber with similar properties to natural rubber, but manufactured without sulphur for vulcanisation.


The metric system unit of force which, when applied to a body having a mass of one kilogram, causes an acceleration of one metre per second squared in the direction of application of the force.

Newton Rings

A visual effect created when the centre of the glass panes making up an IGU come so close as to touch each other. It will appear as a circular or semi circular rainbow effect in the central area of the unit. This may indicate that the spacer width is too small, the result of temperature related pressure changes or improper pressure equalisation.


– National Fenestration Rating Council – the American body which manages the performance ratings of various glass types.

NFRC 100

– The standard specifying environmental conditions, (i.e. wind speeds, internal and external temperatures, solar radiation levels and heat transfer coefficients) and procedure used to determine the performance characteristics of glass types. The Australian glass and glazing industry has adopted the NFRC 100 – 2001 methodology through the AFRC (Australian Fenestration Rating Council).


A small protrusion of glass. See Corners on/off and Flange. Nibs often occur away from the corners of the sheet.

Nickel Sulphide Inclusions (NiS)

Minute particles of nickel and sulphur present in the raw material of glass which under heat, form into crystals and, in rare cases, can cause spontaneous breakage.

Noise Insulation Rating

Capacity to keep the unwanted, outside noise from entering through the glass


Obscure Glass

(See Patterned Glass).

Off-Line Coatings

Applied to individual panes of glass once the glass has been manufactured, taken off line and cut in preparation for further treatment. NOTES: Off-line coatings sometimes called sputter coatings are a soft coat and require special handling and processing. Toughening must take place before the coating is applied.

Offset Intentional mismatch

(see Mismatch).

On-Line Coatings

On-line treatment made while the glass is hot and still in the annealing lehr. They may still be considered as basic products, and the size and tolerance constraints are similar to those for clear float glass. Notes: 1. Surface coatings, either for solar control purposes or for reduced emissivity (a property to improve thermal insulation), are called pyrolitic coatings because they are generally applied to the hot glass during its passage through the annealing lehr. They involve the thermal decomposition of gases, liquids or powders sprayed on to the glass to form a metal oxide layer that fuses to the surface. 2. On-line coatings have advantages of hardness and durability over off-line coatings and are suitable for bending and toughening. They tend to be limited in colour/variety.

One-Way Vision

The term for a reflective glass, which if glazed with appropriate lighting ratios, allows visual security to be maintained from the viewing side.


Applied polyester film or coating to the surface of tinted or reflective glass rendering it opaque. Suitable for use in spandrel and non-vision areas.


The relative capacity of a coating material to obstruct the transmission of light.


Denoting a solid colour with little if any light transmission.

Open Gaseous Inclusions

Open bubbles at the surface of glass, which leave a cavity in the finished surface.

Orange Peel Effect

A rough surface texture on paint or ceramic ink coating having the appearance of orange peel and regarded as undesirable when viewed against light.

Ordinary Annealed Glass

Cooled gradually during manufacture in an annealing operation to reduce residual stresses and strains that can occur during cooling.


In the sense of a film or coating, forming an integral element of a whole.

Overhead Glass

Generally regarded as glass or glazing installed at above 2 metres and sloped more than 15° from the vertical. It relates to glass over populated areas. Vertical glazing to upper levels is not generally regarded as overhead glass.



A process whereby glass is first coated with ceramic enamel, and subsequently fired so that the colour becomes permanent.

Panel Wall

A non-load bearing window wall that is wholly supported at each storey.

Pascal (Pa)

The unit of pressure or stress that arises when a force of one Newton is applied uniformly over an area of one square metre.

Patterned Glass

Having a pattern impressed on one or both sides. Used extensively for diffusing light, privacy, bathrooms and decorative glazing. Sometimes called figured rolled or obscure glass.


Tiny, transparent openings in a coating film which can be attributed to surface contamination, cracks, dirt, coating contamination, surface tension, static electricity, screen clogging, abrasion of the film, agglomerates in the coating, rapid solvent loss, and the like. Any small hole that permits the passage of light.

Plate Glass

The plate glass process was used to produce higher quality glass by the grinding and polishing of both sides, (see Polished Plate) but has now been completely superseded by the float process. Because of the long usage of the term, much currently made Float glass is sometimes still incorrectly referred to as plate glass in specifications.


One sheet or panel of glass in a laminate.

PMMA Resin

PolyMethylMethAcrylate. A very elastic resin used as an interlayer in acoustic laminate where the limpid interlayer has excellent sound reduction properties.

Pocket Glazing

A U-shaped opening in a sash or frame to accommodate a glass panel. Beads maybe fixed or removable.

Poisson’s ratio

The ratio of lateral strain to axial strain in an axially loaded glass sample, derived from modulus data.


A device for examining the degree of strain in a sample of glass. (Either edge or surface compression).

Polished Plate Glass

Manufactured prior to the invention of the Float process. The glass was ground and polished on both sides to produce a parallel optically high quality surface.

Polished Wired Glass

A clear glass that has been ground and polished on both surfaces with a wire mesh embedded into it.


A process whereby the surface or edge of glass is polished with felt and a polishing agent, as in polished edges.

Poly Vinyl Butyral (PVB)

Interlayer An extremely tough, resilient plastic film used to bond glass together in the laminating process.


Compounds made from polybutene polymers.


A butyl compound, typically the primary seal in a dual seal Insulating Glass Unit and the key component in restricting moisture vapour transmission.


A chemical structure consisting of long chains of molecular units.


Compounds made from polysulfide synthetic rubber. A secondary sealant used to seal the perimeter of insulated glass units. Polysulphide must not be exposed to UV otherwise it will breakdown. It can only be used when the IGU is fully framed.

Polyvinyl Chloride (PVC)

Polymer formed by polymerisation of vinyl chloride monomer. Sometimes called vinyl.

Pre-Shimmed Tape Sealant

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


A coating specifically designed to enhance the adhesion of sealant systems to certain surfaces.


A compound used to glaze and seal glass into joinery.


The coating on a glass substrate which is deposited on-line during the glass manufacturing process. The coating is fired into the glass surface at 700°C and is therefore extremely hard and durable.


Quench Pattern

(See Strain Pattern).



The thermal resistance of a glazing system. The higher the R-value, the less heat is transmitted throughout the glazing material. The R-value is the reciprocal of the U-value.


Process by which energy passes from source to object without heating the space between them, e.g. energy from the sun to earth.


Regions of different compositions within the glass mass usually seen as bands of lines parallel to an edge on float glass.


The part of a frame in joinery which is designed to receive glass which can be face putty glazed or receive a removable glazing bead to hold the panel of glass in place.

Reflective Glass

Glass with a reflective coating to reduce heat and light transmission.

Refractive Index

The ratio of the speed of light in air to the speed of light in the glass.


The repair or replacement of glazing because of breakage, renovation or for any other reason.

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 (W/m2 per C°). The lower the relative heat gain the more the glass product restricts heat gain.

Relative Humidity

A measure of the moisture content of the air at a given temperature, in effect the ratio of the water vapour pressure to the saturated water vapour pressure. It is expressed as a percentage.

Reveal Lining

The trim member that lines the perimeter of a window between the frame and the internal wall lining. Also known as a reveal.

Rolled Glass

Glass formed by rolling, including patterned glass and wired glass. (See also Patterned Glass).

Roller Hearth Toughening

A process that supports the glass horizontally on rollers, passing it first into a heating chamber and then into a cooling area. The roller hearth can produce an effect known as roller wave.

Roller Wave

Corrugations, dimpling, embossing or waviness imparted on horizontal heat-treated glass while the glass is transported through the furnace on a roller conveyor. The corrugations produce distortion when the glass is viewed in reflection.

Round and Polish

The grinding in the form of a semicircle and polishing, of the cut edge of the glass. Also known as round smooth. Usually a manual operation.

Round Edge

The slight curving of the cut edge of the glass to form an arc of a circle.


An abrasion or series of small scratches, which produce a frosted appearance in glass. Generally caused during transport by a chip lodged between two panels.


Safety Glass

Glass which is treated or manufactured into a form that reduces the likelihood of a cutting and piercing injury to persons by the glass should it be broken by human contact. These are the manufactured glass types which satisfy the requirements of AS/NZS 2208 for safety glazing. Laminated and toughened safety glass are rated Grade A. Wired glass is rated Grade B.

Safety Mirror

Mirror which has a sheet of organic material permanently bonded to one side so that the mirror holds together if broken and meets the test requirements of the relevant code.

Safety Plastic

A glazing material that is solid in its finished state and at some stage in its manufacture or processing into finished articles, can be shaped by flow. Plastic may consist of a single sheet of plastic material, a combination of two or more such sheets laminated together, or a combination of plastic material and reinforcement material in the form of fibres or flakes, which meets the test requirements of the safety glazing standards.

Safety Wired Glass

A single sheet of glass with wire completely embedded in the glass, which meets the test requirements of the relevant safety glazing standards.

Salt Spray Test

Accelerated corrosion test in which samples are exposed to a fine mist of salt water. Primarily used to test silvered glass.


A surface treatment for glass obtained by blasting the glass with hard particles to obscure one or both surfaces of the glass. The effect is to increase obscurity and diffusion. but it can make the glass weaker and harder to clean.


The separate frame to a window or door which carries the glass. It may be fixed (inoperable) or movable (operable).


A smooth, lustrous texture.


Uneven edge definition in a screen-printed design caused by inadequate thickness of emulsion or insufficient exposure of the emulsion which results in the emulsion, during washout operations, to break free of an entire mesh opening, following the contour of the mesh instead of the contour of the image. Most obvious with coarser meshes where the pattern steps over a thread.


Scratch on the surface of the glass.


Any marking or tearing of the surface appearing as though it had been done by either a sharp or rough instrument. Scratches occur on glass in all degrees from various accidental causes. Block reek is a chain-like scratch produced in polishing. A runner-cut is a curved scratch caused by grinding. A sleek is a hairline scratch. A crush or rub is a surface scratch or series of small scratches generally caused by handling.

Screen Printing

The application of ink to the surface of glass through a screen or mesh. The ink may be applied uniformly to the entire surface or in a design determined by the mesh stencil.

Screw-on Bead or Stop

Stop, moulding or bead fastened by machine screws as compared with those that snap into position without additional fastening.


An abrasion or dull area on a glass substrate, usually caused by furnace rolls or contact with other furnace parts during heat-treating cycle.


A dull area in a glossy coating film.


Compound used to fill and seal a joint or opening, in contrast to a sealer, which is a liquid used to seal a porous surface. When cured, it has adhesive and flexible properties.

Security Glass

Thick laminated or multi-laminated glass designed to withstand various forms of violent attack. (Specialist advice should be obtained to assist in the selection of this product).


Small gaseous bubbles usually less than 2 mm in size (see blister and bubble).

Segmented Glazing

See Faceted Glazing.


The extreme lateral edges of the Lehr or glass ribbon which are stripped off and recycled as cullet.

Serviceability Wind Pressure

The wind pressure conditions that glass meets in normal ‘in service’ conditions. It is the wind pressure used for deflection calculations.

Setting Blocks

Generally rectangular cured extrusions of santoprene, EPDM, silicone, rubber or other suitable material on which the bottom edges of glass are placed to effectively support the weight of the glass and avoid frame contact.

Shading Coefficient

The ratio of the total solar heat gain through a specific glass product or glazing system to the total solar heat gain through 3mm clear glass under the same set of conditions; often quoted in terms of ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers) or standard weather conditions.

Shark’s Teeth

Serrated features in the cut edges of glass, extending from the score mark through part or all of the thickness. Shark’s teeth seriously weaken the edge and create thermal shock risk.

Sheet Glass

A transparent glass manufactured by drawing. Sheet glass has natural fire finished surfaces, but because the two surfaces are never perfectly flat and parallel there is always distortion of vision and reflection.


Similar to a chip, but often larger and occurring on the face opposite to the score mark.


(See Spacers).


The glazed or partly glazed wall at public access level in non-residential buildings with or without a stall board and /or intended for the display of goods or services.

Shore ‘A’ Hardness

Measure of firmness of a compound by means of a Durometer Hardness Gauge (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. )

Side Panel

A panel (operable or inoperable) located adjacent to a doorway. It may or may not be in the same plane as the doorway.

Sight Line

The line along the perimeter of the glazed panel corresponding to the edge of fixed or removable bead. The line to which sealants contacting the glazed panel are sometimes finished off. It tends to be the daylight size.

Sight size

The clear unsupported opening size that admits light.


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

Silicone Sealant

One part or two part elastromeric adhesive, rubber sealant which cures at room temperature, also referred to as room temperature vulcanising (RTV). Its inorganic composition means silicone sealant is unaffected by UV, ozone and extremes of hot and cold. It will not break down or lose adhesion and for this reason is widely used in most glazing applications.


The bottom horizontal member of the window/door frame.


The application by chemical or other methods of a film of silver to a glass surface to create mirrors.


Streaks of dense seed with accompanying small bubbles.


A fine scratch-like mark having smooth boundaries, usually produced by a foreign particle in the polishing operation.

Sloped Glazing

Any installation of glass that is sloped more than 15° from the vertical. Where over populated areas, refer Overhead Glazing.

Slump Glass

Glass that has been heat treated to mould patterns or designs into the surface of the glass.(See also Formed glass)


A defect in a coating caused by accidental handling or movement of the printing screen or substrate during application of the coating film. May also be caused by momentary sticking of the printing screen to the printed substrate during the print stroke.


Streaked areas appearing as slight discolouration.

Soda-lime Glass

The most commonly melted form of clear, uncoloured flat glass, so-called because a principal ingredient besides sand, is lime.

Soft Coats

Coated glass where metal particles have been deposited on the glass by a chain reaction in a vacuum vessel. This is done off line and is sometimes called sputter coating. The coating is soft and less durable than hard coats.

Solar Control Glass

Tinted and/or coated glass that reduces the amount of solar heat gain transmitted through it.

Solar direct transmittance

The fraction of solar energy, at normal incidence, that is transmitted directly through the glazing.

Solar Energy Spectrum

Radiation having the same spectral distribution as the total radiation that is received at sea level directly from the sun at an altitude of 30°. Solar radiation is divided into three portions namely, ultraviolet (300-380 nm), visible (380-780 nm) and infra-red (780-2100 nm). All three categories result in heat gain when the solar radiation is absorbed. At the earth’s surface, approximately 3% of the solar radiant energy is ultraviolet, 44% is visible and 53% is infra-red.

Solar Energy Transmittance

The percentage of ultra-violet, visible and infra-red energy within the solar spectrum that is transmitted through the glass.

Solar Heat Gain Coefficient (SHGC)

The ratio of directly transmitted and absorbed solar energy that enters into the building’s interior (when compared to an open space). Solar heat gain includes directly transmitted solar heat and absorbed solar radiation which is then re-radiated conducted or convected.

Solar Heat Transmission

The amount of solar energy transmitted directly through glass, compared with the total solar energy impinging on the exterior glass surface. It is typically expressed as a percentage.

Solar Reflectance

The percentage of solar energy within the solar spectrum that is reflected from the glass surfaces.

Solar Total Transmittance

The fraction of solar energy, at normal incidence, that is transferred through the glazing directly by transmittance and indirectly by absorbed energy that flows inward by re-radiating, assuming a specified wind speed.


The component of an insulating glass unit which separates the glass and includes a desiccant, with additional sealant material to prevent air and water penetration.

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.


The dimension between supports. For panels supported on all four edges, it corresponds to the smaller of the sight size dimensions. For panels supported on two edges, it represents the dimension between the supports.

Spandrel Glass

The panels of an exterior wall which conceal structural columns, floors and shear walls located between vision areas of windows.

Spontaneous Breakage

A term applied when toughened glass fractures for no immediately obvious reason. Note: Breakage is usually caused by impact damage, edge damage, poor glazing or incorrect design, but occasionally it is due to foreign particles in the glass. The reason is often not obvious because toughened glass disintegrates after fracture, making the cause difficult to ascertain.


The process in which, by passing an electric current through an ionised gas and thus bombarding the surface of a metal cathode with ions, atoms of the desired metal are vapourised and then deposited in a thin film on the surface of glass. Also known as soft coats. Stain Discolouration of either a glass or finished aluminium 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 Glass

Refers to the craft of lead-lighting – glass which is coloured by fusing pigments to the surface, or windows made up of pieces of stained glass in lead canes.

Stall Board

An upstand, frame, or raised structure above the finished floor level on which a shopfront is fixed. Sometimes called a nib or nib wall.

STC (Sound Transmission Class)

A single number rating derived from individual transmittance losses at specified test frequencies. 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 (1Hz) at which it is measured and it is expressed in decibels (dB). Also called Transmission Loss (TL).


Any crystalline inclusion embedded in the glass.


Deformation due to stress.

Strain Point

Temperature at which the viscosity of the glass is approximately 1014 poises. At the strain point of glass, internal stresses are substantially relieved in a matter of hours.


Elongated defects in glass.

Stress (Residual)

Any condition of tension or compression existing within the glass, caused by incomplete annealing or induced temperature gradient during the manufacture of heat-treated glass.

Stress Pattern

A specific geometric pattern of iridescence or darkish shadows that may appear under certain lighting conditions, particularly in the presence of polarised light (also called quench pattern). The phenomenon is caused by the localised stresses imparted by the rapid air cooling of the toughening operation. Stress pattern is characteristic of all heat treated glass.

Striking Off

The operation of smoothing off excess compound at sight line when applying compound around lights or panels.


Transparent lines appearing as though a thread of glass has been incorporated into the sheet (see wire line, ream and cords).


Wavy, transparent lines appearing as though a thread of glass had been incorporated into the sheet (see also ream).

Structural Glazing

Glazing system used in place of a conventional joinery or curtain wall to install glass products on to structurally supporting sub-frames, or fins, to achieve a flush continuous glass system.

Structural Members

The elements such as mullions, transoms and sash-rail, that can be demonstrated to form the function of a mullion or transom.

Structural Sealant

An elastomeric adhesive sealant that is capable of being used as both a weather seal and a structural component of a glazing system.

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.


Refers to the type and thickness of glass expressed in mm.


A base material to which other materials are applied.

Surface Compression

The compressive stresses built into the surface of glass. A balancing force to centre tension in the glass.

Surface Position

Generally a number denoting which face of a pane of glass or insulating glass unit the coating side or patterned side should face.


Any frame, sash, casement or other building component into which glass is glazed.



A straight line extending from the arc of a curve or bend.

Temper (Toughen)

Inducing predictable residual stresses in glass by controlled chilling from near the softening point to below the strain point. These residual stresses are in compressive form on the surface of the glass and tensile in the interior. The compressive stress on the surface strengthens the glass.

Tempered Glass

(See Toughened glass).


A pattern used as a guide to produce the desired definition of the overall size and shape of a piece of glass.

Thermal break

An insulating material of low thermal conductivity placed between materials of high thermal conductivity within the system itself to inhibit the flow of cold or heat. Also known as ‘thermal stress crack’ in glass.

Thermal Coefficient of expansion (linear)

The fractional change in length of a uniform length of glass per expansion (linear) degree of temperature variation.

Thermal Resistance

The relative ability of glass to withstand thermal shock.

Thermal Safety Assessment

A method of assessing the risk of glass breakage from thermal stresses which may be present from location and environmental factors.

Thermal Stress

Stress generated in glass as a consequence of temperature differentials such as hot centre of glass and cold edges (in the frame) resulting from absorbed radiation and increases in temperature.

Thermo Plastic Spacer (TPS)

is a butyl-based thermoplastic material, with an integrated dessicant used in IGUs as an alternative to metal spacers.

Thermoplastic Spacer (TPS)

A material used as the primary seal in Insulated Glass Units. A butyl-based thermoplastic material. It is UV stable with integrated desiccant. It is a non-metallic spacer offering the ultimate in heat insulation.


Range of thicknesses that are available

Tight Size

The actual size of the rebate opening from one side to the other without any clearance.

Tinted Glass

Glass with colourants added to the basic glass batch that give the glass colour, as well as light and heat reducing capabilities. The colour extends throughout the thickness of the glass. Typical tints include bronze, grey, dark grey, aquamarine, green, deep green and blue.

Toned Glass

See Tinted Glass

Tong Marks

Small, surface indentations near and parallel to one edge of vertically toughened or vertically heat strengthened glass resulting from the tongs used to suspend the glass during this method of heat treatment.

Total solar energy reflected

The ratio of the solar energy that is deflected by the window to the total solar energy impinging on the window. It is typically expressed as a percentage.

Toughened Glass

Flat or curved glass that has been heat-treated to induce a high surface and /or edge compression. Fully toughened glass, if broken will fracture into many small pieces (dice) which are more or less cubical. Fully toughened glass is approximately 4 to 5 times stronger than annealed glass of the same thickness when exposed to uniform static pressure loads. It is sometimes called ‘Tempered glass’.

Toughened Laminated Safety Glass

Laminated safety glass utilising two panels of toughened safety glass in the make-up.

Toughened Safety Glass

Glass converted to a safety glass by subjection to a process of pre-stressing so that, if fractured, the entire piece disintegrates into small, relatively harmless particles.


The quality of a film or substrate, which determines the transmission or diffusion of light.

Translucent Glass

Glass that transmits light with varying degrees of diffusion so that vision is not clear.


A horizontal intermediate framing member.


U Value

A measure of air-to-air heat transmittance (loss or gain) due to 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 better the insulation.

ULS Ultimate Limit State

The wind pressure or load at which failure of the integrity of the glazing can be expected. The same as UWP.

Ultra-Violet (UV)

The name of the solar radiant energy that is the invisible portion of the light spectrum with wave lengths shorter than 380 nanometres, which is the dominant influence in fading.


(See Insulating Glass Unit).

UWP Ultimate Wind Pressure

The wind pressure or load at which failure of the integrity of the glazing can be expected. The same as ULS.


Vacuum Coated

The process in which, by passing an electric current through an ionised gas and thus bombarding the surface of a metal cathode with ions, atoms of the desired metal are vapourised and then deposited in a thin film on the surface of glass. Also known as soft coats and sputter coated glass.

Vented Inclusion

Crack in the glass surface caused by the existence of an inclusion.

Ventilated Airspace

The space between blind/drapes and the window or between spandrel glass and the structure of the building. The thermal safety of the glazing will be dependent upon the extent of ventilation. Unventilated spaces can lead to significant heat buildup in the cavity.


Small cracks at the edges of glass that can lead to breakage.

Vertical Toughening

Percentage of visible light passing directly through the glass. The wave length range for visible light is 380 to 780nm. The higher the percentage the more daylight.

Vinyl Back Mirror

Mirror which has a sheet of organic material permanently bonded to one side so that the mirror holds together if broken and meets the test requirements of the relevant code.

Vinyl Glazing

Holding glass in place with extruded vinyl channel or roll-in type.


The term used to designate the degree of fluidity of a liquid.

Visible Light (Solar Energy)

The portion of the solar spectrum that is visible to the human eye (380-780 nm).

Visible Light Reflectance

The percentage of visible light (380 to 780 nanometres) within the solar spectrum that is reflected from the glass surface.

Visible Light Transmittance

The percentage of visible light (380 to 780 nanometres) within the solar spectrum that is transmitted through glass.



– Window & Door Industry Council. A service organisation for timber window and door manufacturers, supplying products to the building and construction industry.


Refers to the type of spacer material used to separate the panes of glass (or glazing) in an insulated window unit. If the material conducts less heat or cold than a conventional aluminium spacer at the edge of the glass, it is said to be ‘warm-edge’.


The easily seen deviation, undulation or twist from the pure plane of the surface of a sheet of glass.

Weather Seal

A material included in window and door construction to reduce the air infiltration or improve water penetration resistance of the unit. Also known as a sealant joint between panes of glass.

Weep Holes

Small holes or slots in the sash or framing system which allows water to drain to the building exterior.


Window Energy Rating Scheme.

Wet Seal

Application of an elastomeric soft sealant between the glass and frame to form a weather-tight seal.

WHP Laminate

An automotive quality laminate with high penetration resistance and high light transmission (Windscreen High Performance).

Wind Zones

Those areas designated by Local authorities or Specifying authorities as subject to specific ranges of wind pressure and loads.

Window Rating

The level of performance for strength, weatherproofness, insulation or solar control of windows and doors as determined by test. Window ratings for housing are expressed in wind classification terms, and window ratings for buildings other than housing are expressed in design wind pressure terms.

Window wall

A series of multi-light windows, generally spanning from floor to ceiling, and often continuous horizontally.

Window/door assembly

A complete unit comprising frame, couplings, sashes, glazing infill panels and hardware.

Wire line

An attenuated, glassy inclusion that processes optical and other properties that differ from the parent glass. It is generally in a straight line parallel to the direction of draw, and associated with partially or completely dissolved stones (see cords, strings and ream).

Wired Glass

Having a layer of meshed or stranded wire embedded near to the centre of thickness of the panel. This glass is available as polished glass (one or both surfaces polished to make it clear) and patterned glass.

Working Life

The time during which a curing sealant (usually of two compounds) remains suitable for use after being mixed with a catalyst.

Working point

Temperature at which the viscosity of the glass is approximately 104 poises.


X-Ray Shielding Glass

Contains a high percentage of lead and sometimes also barium and which has a high degree of opacity to X-rays. The opacity is usually expressed in terms of the thickness of metallic lead, which would give equal absorption of X-rays of stated wavelength.


Young’s modulus

The ratio of stress to strain.