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

Acid Etching

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

Acoustic Laminate

Laminated glass with a special acoustic interlayer for superior sound control.


Self-Cleaning Glass. Its dual action uses the forces of nature (natural ultraviolet light and rain) to help keep the glass free from organic dirt. Manufactured by Pilkington.


Asahi Glass Company. An International Glass Manufacturer. Previously Glaverbel.


The gap between two pieces of glass in an insulated glass unit.

Ambient Temperature

The surrounding temperature existing at any given time.

Annealed glass

Technical definition of the stress condition of ordinary glass.


Process designed to eliminate or limit stresses in glass by submitting the glass to strictly controlled cooling in a special oven known as a lehr.

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 & processing.


Pyrolytic coated reflective glass. Manufactured by St Gobain. Refer Stopsol.


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.


The original Pilkington UK name for tinted float glass. Manufactured by Pilkington.


An obscure glass with a non-directional pattern. Cannot be toughened. Manufactured by Pilkington.

Argon Gas

An inert, nontoxic gas used to fill insulating units, thus improving thermal performance.

Arrised edge

The result of removing sharp edges on glass.


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


International glass manufacturer.


American Society of Heating, Refrigeration and Airconditioning Engineers.

Aspect ratio

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


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


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


Back Clearance

Space between the back of the glass and 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 in the joint to control sealant joint depth, provide a surface for sealant tooling, and to prevent three-sided adhesion.


A framed or unframed enclosure between handrail and floor level (see also handrail). Required to protect a difference in level of 1m or more.


An Italian manufacturer of specialised glass machinery.


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).

Bent Glass

Bending or curving glass using heat process.


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. Usually mirrors.


The amount of overlap between the frame or fin support. 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.


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


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


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


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

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. Refer to Tinted Glass.


European manufacturer and distributor of glass equipment and hardware including UV glue technology.


Heat resistant glass. Manufactured by Schott.


Low expansion heat resistant glass. Manufactured by Schott.


A curve, bend or other deviation from straightness or flatness.

Break pattern

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

Breather Tube

A tube, factory-placed into an IGU 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. Refer to Capillary Tube.

Brewster’s Fringes

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

Bronze glass

See tinted glass and body tinted glass.


Gaseous cavity In float glass and obscure glass. In laminated glass, a gas pocket in the interlayer material or between the glass and the interlayer.

Bull Nose

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

Bullet Resistant Glass (BRG)

A multiple lamination of glass and/or 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 the centre for decorative effect. Originally the cut out bottom of a mouth blown glass cylinder.


Nylon or hard plastic or fibre used around fixings in holes to prevent glass to metal contact. Similar to Grommet.

Butt Glazing

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



Abbreviation for Cut-To-Size glass.

CAD Drawing/Processing (Computer Aided Design)

The use of a computers to produce shapes and graphics.

Cantilevered Balustrade

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

Capillary Tube

A very small metal tube of specific length and inside diameter factory-placed into the IGU spacer to accommodate pressure differences encountered in shipping to high or low altitudes. Refer to Breather Tube.

Casement window

A window pivoted or opening on side or top hinges.

Cast glass

Glass produced by ‘casting’, in other words by pouring molten glass into a mould or by heating glass in a mould until it assumes the shape of the mould.


An obscure glass with a non-directional pattern.

Centre tension

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

Ceramic enamel

An organic and essentially non-metallic coating fused to a substrate which consists of a glass frit and inorganic pigments. Also known as ceramic ink, paint or frit.

Ceramic Frit

Particles of glass that are mixed with paint applied to the surface of a piece of glass. The Frit has a low melting point and permanently bonds to the glass during the tempering process.

Cerium oxide

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

Channel depth

The measurement from the bottom of the channel of a frame to the top.

Channel opening

The internal horizontal dimension between the upstands of the channel.

Channel Width

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 the void it has left.


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 safety glass product. Discontinued in South Africa.

Cladding Glass

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


Clear Low E glass. Manufactured by Guardian.


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

Coated Surface

The surface of the glass which is coated.

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 or used inside an IGU. Similar to Muntin Bars.


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


The ability of the glass or glazing to prevent people falling through.


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


Soft coat reflective glass. Manufactured by St Gobain.

Copper Free

A type of mirror not containing copper as one of its back coatings.

Countersunk hole

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


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 in a float glass manufacturing line 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.

Curved glass

Glass which has been heated past its softening point and formed into a curved shape. Refer to Bent Glass.

Cut sizes

Any flat glass cut to specific dimensions. Refer to Cut To Size.


The removal of a section of a glass panel.


A person who cuts glass or a tool used to cut glass.


Scoring glass and breaking it along the score line.

CVD Coatings

Chemical Vapour Deposit. Refer to Pyrolytic Low E coatings


Daylight Size

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

Decorative glass

Glass or patterned glass processed by craftsmen for decorative effect. Stained glass, lead lights, sand blasted, acid etched, embossed, slumped, and printed glass fall into this category.

Deep Etch

An extra deep sandblast used to create depth in an image on glass.


The amount of bending or flexing of the centre of a glass panel perpendicular to the plane of the glass surface under load.


A condition in which one or more of the glass plies of laminated glass loses the bond with the interlayer.


Molecular sieve or extremely porous crystalline substance used to absorb moisture inside the air space of secondary glazing or an IGU.

Design wind pressure

The specified wind pressure a product is designed to withstand.

Dew point

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


Low Iron extra clear glass. Manufactured by St Gobain.

Diffuse Reflection glass

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.

Direct Radiation

The emitted solar radiation that reaches the earth surface from the sun. About half of the radiation is in the visible short-wave part of the electromagnetic spectrum. The other half is mostly in the near-infrared part, with some in the ultraviolet part of the spectrum.

Direct Transmission

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


Alteration of viewed images caused by variations in glass flatness It is an inherent characteristic of glass that has been toughened.

Dorma Window

An upright window formed in a sloping roof.

Double Glazing

In general, two panes of glass separated by an air space within an opening to improve insulation against heat transfer and/or sound transmittance. Normally a referred to as an Insulating Glass Unit. Refer to IGU.

Drop Height

The vertical height an impact ball is raised for testing safety glass.

Dry Glazing

Also sometimes 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.

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

An instrument for measuring Shore Hardness and the relative hardness of materials such as rubber.


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

DXF File

A computer drawing of a shape that can be processed by a CNC machine.


Eclipse Advantage

Low E glass with a reflective coating. Manufactured by Pilkington.

Edge Blocks

Blocks that prevent the glass moving sideways.

Edge Clearance

The space between the edge of the glass and sight line.

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 at the edge that include vents, shells, flakes, nips and corners on/off.

Edge delamination

A condition in which one or more of the glass plies of laminated glass loses the bond with the interlayer.

Edge deletion

The removal of the coating around the periphery of a soft coated glass prior to assembly into an IGU.

Edge Banding

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 or for visual effect.


Grinding, smoothing, bevelling, mitre, or polishing edges of glass panes.


An elastic rubber like substance or synthetic rubber.


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 reradiate absorbed energy (heat).

End Caps

A set number of stock sheets of glass packed with wooden caps on each end of the glass which is then strapped together to hold them in place. This form of packaging makes for easy unpacking at the user’s end.

Energy Advantage Low E

Low E glass. Manufactured by Pilkington.


Abrading the surface of the glass to produce decorative designs.


A synthetic rubber used to produce gaskets and setting blocks.


A stable situation in which forces cancel one another.


To alter the surface of the glass with acids or special tools.

Euro Grey

The generic name for the colour of standard grey tinted float as marketed in Europe and America.


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 terms: Bubble, Blemish, Bloom, Seed, Chip and Feather.


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

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 Resistant Glass

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

Fire-rated glass

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

Fire-resistant 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.


An impervious membrane or material which must be compatible with the framing materials, installed in such a manner as to waterproof the installation in the building.

Flat Glass

A general term that describes 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.


An obscure glass with a semi-transparent directional pattern.

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.

Formed glass

Glass which has been heated and formed by moulds. Similar to Slumped glass.

Fracture pattern

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


The rate of vibration of a sound wave measured in Hertz (Hz).


Raw materials mixed together and melted to form glass.

Front clearance

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

Front putty

A triangular fillet of putty formed between the surface of the glass and rebate platform.

Frosted Film

A decorative film applied to glass after glazing.

Frosted Finish

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

Fully Tempered glass

Toughened safety glass.


Gas filled

The filling of the cavity of a sealed IGU with a special gas to enhance the thermal insulation. An example of this is Argon gas.


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

Georgian wired glass

Glass with an incorporated wire mesh square pattern. The glass may be cast obscure or clear polished.


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, luminaries, sky, 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 to fit with masonry 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. Also known as Glass Brick.

Glass polycarbonate composite

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 Fins

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

Glazing bar

An aluminium extrusion typically used for glazing systems in roofs.

Glazing quality

The standard float glass quality supplied to buildings when quality is not otherwise definitely specified. Same as FRQ.

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 other materials that fills a window opening.

Green hue

The green appearance of float glass due to the inclusion of iron.

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.

Guardian Industries

International Float glass manufacturer of high quality glass products.


Half Round

Rounding of a cut edge to a quarter circle. Similar to Bull nose.


A horizontal or sloped rails for support on a stair landing or balustrade.

Hard coat

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

Heat absorbing glass

Glass that absorbs amounts of solar energy. Refer to 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. Refer to Insulation.

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 transferred by one of three mediums, Conduction, Convection or Radiation.

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 (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.

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.


Term used for self-cleaning glass in which the coating attracts water so that it spreads to form a thin film to wash away dirt and dries without spotting.



A crystalline or non-crystalline particle entrapped in glass. Can be nickel sulphide.


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

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 or double glazing.


The time of a fire resistant glass material to resist the passage of flame and hot gas.


Material used between two or more glass panes in the manufacture of laminated safety glass to bond the glass together. Can be polyvinyl butyral (PVB) or Ethylene-vinyl acetate (EVA) or Urethane.

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.

IT shield glass

Electromagnetic data shielding glass to prevent electronic eavesdropping.



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



Hard coat Low E glass. Manufactured by Pilkington.


Laminated Safety Glass

A product consisting of two or more sheets of glass permanently bonded together by an interlayer material – PVB- and usually meeting the test requirements of SANS 1263-1/2 or 3.

Lead glass

A type of glass produced with lead oxide in the mix for X ray shielding applications.


Glazing made in the traditional manner with lead frames and small pieces of glass.


A special type of oven or kiln used for annealing glass.

Lehr end size

The standard dimension size produced by the cut length and lehr width of a float line.

Lehr width

The specific width of the furnace or annealing ribbon which designates the sizes available from that float line. Refer to annealing.

Light transmission

The amount of visible light transmittance through a type of glass, usually expressed as a percentage. Also known as light transmittance. Refer to VLT.

Linear Expansion

The expansion of a material over its length per degree C change in temperature.

Liquid laminated safety glass

Two or more sheets of glass permanently bonded together by a liquid resin that cures to form a plastic-type interlayer. Discontinued in South Africa.


An Austrian manufacturer of specialized glass processing machinery.


A panel or sheet of glass.

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.

Location Blocks

Blocks positioned between the frame and edge of the glass to maintain its position.

Long wave radiation

The part of the electromagnetic spectrum (5000 to 50000nm wavelength) which is produced by objects at around room temperature. Normal glass is transparent to this radiation and Low E glass is designed to reflect it.


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

Low E

Refer to Low emissivity glass.

Low emissivity glass (Low E)

Commonly known as ‘Low E’ glass and often used in double glazing units, this 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

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



Heavy consistency compound which may retain adhesion and pliability with age.


Acid etched glass manufactured by AGC.

Med X

Lead X ray glass manufactured by Pilkington.


Glass silvered on one side.


Misalignment of the edges of two panes of glass in laminated glass or in Insulating Glass Units.


An obscure glass with a non-directional pattern. Also known as Pacific. Manufactured by Pilkington.

Mitre bevel

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


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


Laminated glass comprising three or more lites of glass.

Muntin bars

Bars used in insulated glass units to simulate colonial style windows.


Narrow Reeded

An obscure glass with a directional pattern Also called Slender Vue.


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

Newtons rings

Coloured rings which appear when two pieces of glass are pressed together.


A small protrusion of glass away from the corners.

Nickel Sulphide Inclusions

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 in toughened glass.

Nominal thickness

The commonly used dimension by which the thickness of a panel of glass is sold or marketed. Note: The actual thickness of a particular pane of glass may not coincide with the nominal thickness and be subject to the manufacturer’s tolerances.


Obscure Glass

See Patterned Glass.

Off-line coatings

Coatings applied to individual panes of glass once the glass has been manufactured then moved off- line and cut in preparation for further treatment. Note: Off-line coatings are sometimes called sputtered coatings or soft coat and require special handling and processing.

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. Light ratio usually 6:1.

On-line coatings

On-line coatings are made while the glass is hot and is 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. Surface coatings, either for solar control purposes or for reduced emissivity (a property to improve thermal insulation), are called pyrolytic 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, forming a metal oxide layer that fuses to the surface. On-line coatings have advantages of hardness and durability over off-line coatings and are suitable for bending and toughening.


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


Denoting a solid colour with little if any light transmission.


Clear float glass manufactured by Pilkington.


Low iron glass manufactured by Pilkington.

Overhead glass

Any glass which is flat or inclined and above head height.



An obscure glass with a non-directional pattern Manufactured by Pilkington. Refer to Mistlite.


European range of grey, bronze, green and pink colours. Manufactured by St Gobain. Refer to Tinted Float.

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.

Patch Fitting

A frameless glass fitting, typically for hinged frameless doors.

Patterned Glass

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


Process used for self-cleaning glass to loosen and break down organic dirt particles on the glass surface.

Photovoltaic Glass

Glass with integrated solar cells, to convert solar energy into electricity. This means that the power for an entire building can be produced within the roof and façade areas.


International Float glass manufacturer.


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.


Frameless glass system using countersunk fittings. Manufactured by Pilkington.


European range of clear and tinted float. Manufactured by Glaverbel. Refer to Tinted Float.

Planibel Low E

Sputter coated Low emissivity glass. Made by AGC Refer to Low emissivity glass.

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, float glass is sometimes still incorrectly referred to as plate glass in specifications.


One sheet or panel of glass in a laminate.


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

Polarised Light

Light waves which are vibrating in a special orientation either after passing through a polarised filter or after being reflected a surface or from the sky.

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. Also known as Plate glass.

Polished Wired Glass

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


A process whereby the surface or edge of glass is polished as in polished edges.


Polished All Round.


Polished 2 Long dimensions.


Polished 1 Long dimension.


Polished 1 Long 1 Short dimensions.


Polished 2 Short dimensions.

Polyvinyl Butyral (PVB)

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

Polyisobutylene (PIB)

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


A sealant used around the perimeter of insulated glass units.

Primary Seal

A butyl-based sealant applied to the edges of the space bar during assembly into double-glazed units, to ensure a watertight and airtight seal around the perimeter of the unit.


A coating specifically designed to enhance the adhesion of sealant systems to glass and/or framing.


A compound used to glaze and seal glass into joinery or steel frames.

Pyran S

Tempered heat resistant safety glass. Manufactured by Schott.


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 ºC and is therefore extremely hard and durable.



The cooling area of a toughening furnace.

Quench Pattern

See Stress Pattern.



A shape where one edge is longer than its parallel with 2 square corners.


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.

Rebate size

The actual size of the glazing rebate opening.

Reflective glass

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


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

Relative Heat Gain (RHG)

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 the more the glass product restricts heat gain.

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.

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.


Overhead glazing to allow natural light into a building.


An obscure glass with a non-directional pattern sometimes referred to as Double rolled Roughcast.


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.


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.


Safety Glass

Glass which is treated or manufactured into a form that reduces the likelihood of 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 SANS 1263-1/2/3 for safety glazing.

Safety mirror

Mirror which holds together if broken and meets the test requirements of SANS 1263-1 . Refer to Vinyl Back mirror. Can also be laminated.

Salt Spray Test

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


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).


An obscure glass which has been acid etched.


Italian manufacturer of glass edging and drilling machinery.

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.


An abrasion or dull area on the glass surface usually caused by furnace rollers or contact with other furnace parts.


Compound used to seal or fill joints or openings. When cured it has flexible adhesive properties.


To grind, usually with an abrasive belt, wet or dry, to remove the sharp edges of the glass.

Secondary Seal

A sealant applied to the edges of double-glazed units after the primary seal, to provide effective and durable adhesion between the glass components and spacer bar.

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 in glass, normally less than 2mm in size.

Self-cleaning glass

Its dual action uses the forces of nature – natural ultraviolet light and rain – to help keep the glass free from organic dirt.


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

Setting Blocks

Generally rectangular cured extrusions of Santoprene, EPDM or 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 (SC)

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.


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


(See Spacers).


Fenestration for the display of products and surfaces.

Shore ‘A’ Hardness

Measure of firmness of a compound by means of a Durometer Hardness Gauge (A hardness range of A) A hardness of 90 is recommended for all glazing.

Short wave radiation

The part of the electromagnetic spectrum (280 to 2500nm wavelength) which is radiated by the sun.

Sight Line

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


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 elastomeric adhesive, rubber sealant which cures at room temperature. Its inorganic composition means silicone sealant is unaffected by UV, ozone, and extremes of hot and cold. Further 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. Refer to Mirror.

Sloped Glazing

Any installation of glass that is sloped more than 15° from the vertical. Where overpopulated areas refer to Overhead glazing.

Slump glass

Glass that has been heat treated to mould patterns or designs into the surface of the glass.

Soda lime silicate glass

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

Soft coated

Coated glass where metal particles have been deposited on the glass by a chain reaction in a vacuum vessel. This is done offline and is sometimes called sputter coating. The coating is softer 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 E

Solar Low E glass manufactured by Pilkington.

Solar Energy Reflectance

The percentage of solar energy of the solar spectrum that is reflected from the glass surfaces. Includes UV, light, and heat.

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 (380-789 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 solar energy within the solar spectrum that is transmitted through the glass. Includes UV, light, and heat.

Solar Heat Gain Coefficient

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 inward. Same as G Value or Solar Factor.

Solar Heat Transmission

The amount of solar heat energy transmitted directly through glass. It is typically expressed as a percentage.

Solar Total Transmission

The amount of solar heat energy that is transferred through the glazing directly by transmittance and indirectly by absorbed energy that flows inward by re-radiating.


A reflective laminated glass produced by PFG.


The component of an insulating glass unit which separates the glass and includes a desiccant. Refer to Airspace.

Spacers (Shims)

Small blocks of neoprene. EPDM, silicone, or other suitable material, placed on each side of the glass product to provide glass centring, 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.


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

Spider Fitting

A fitting with two – four legs which holds frameless glass in place.

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.

Sputtered coated

Performance glass that has undergone the process in which, by passing an electric current through an ionized gas and thus bombarding the surface of a metal cathode with ions, atoms of the desired metal are vaporized and then deposited in a thin film on the surface of glass. Also known as soft coats. Refer to Soft coated.

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 cames.


An obscure glass with a non-directional stippled pattern.

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).

Stock sheet

A whole sheet of glass in various stock sizes depending on product and thickness.


Any crystalline inclusion embedded in the glass.


Hard coat Pyrolytic Reflective Glass. Manufactured by AGC.

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. Similar to Quench pattern.

Structural glazing

Glazing system used in place of a conventional joinery or curtain wall to install glass products on to structurally supporting sub-frame or glass fin with the retention of the glass maintained by the insertion of mechanical fixings , fittings or silicone.

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.


Energy efficient reflective glass with high light transmission. Manufactured by Guardian.

Supersilver (Stopsol)

Reflective tinted glass manufactured by AGC.

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. Sometimes abbreviated to #1, #2, #3 or #4.



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


Electrical conducting glass. Manufactured by Pilkington.

Temper (Toughen)

Introduction of 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. Refer Thermo-Safe GP® toughened

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 a system or extrusion to inhibit the flow of cold or heat.

Thermal coefficient

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-Safe GP®

A range of toughened and laminated glass products produced by Glass Partners.

Tight size

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

Tinted Float

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.

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.

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’. Refer to Thermo-Safe GP®.

Toughened Laminated Glass

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

Translucent Glass

Glass that transmits light with varying degrees of diffusion so that vision is semi-transparent.

Transparent glass

Glass that transmits light and permits clear vision through it.


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.

Ultra-violet (UV)

The name of the solar radiant energy that is the invisible portion of the light spectrum with wave lengths between 300 and 380 nanometres.


See Insulating Glass Unit and IGU.

UV Elimination

The amount of UV light eliminated by the glass as a percentage.


V Cut

A V shape cut into the surface of the glass to create a design. Similar to Brilliant Cut.

Vacuum coated

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


Coloured PVB interlayer for laminated glass manufactured by Eastman.

Venetian Mirror

A mirror which has strips of clear glass between which allows better viewing from one side and provides a measure of one way vision.

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 build-up in the cavity.


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


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

Visible Light Reflectance

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

Visible Light energy

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

Visible Light Transmittance

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


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 allow water to drain to the building exterior. Same as Drain holes.

Wet Glaze

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

Wet seal

A mirror which has strips of clear glass between which allows better viewing from one side and provides a measure of one way vision.

WHPR laminate

An automotive quality laminated safety glass with high penetration resistance and high light transmission.

Wind load

The pressure acting on an external surface of a building caused by the direct action of the wind.

Wind zones

Those areas designated by local building authorities or specifying authorities as subject to specific ranges of wind pressure and loads.

Wired Glass

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.


X-Ray Shielding glass

Glass that 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.