GLOSSARY

Absorption
The incident radiation that is absorbed by the glass and reradiated either inside or out.

Acid Etched Glass
A translucent glass produced by acid-etching one surface of the glass, giving it a satin like surface.

Airspace
The cavity between two panes of glass in an insulated glass unit, which is hermetically sealed or filled with special gases.

Annealing
Process to limit stresses in glass by submitting the glass to controlled cooling in a special oven known as a lehr.

Argon Gas
Argon is the third noble gas, in period 8, and it makes up about 1% of the Earth’s atmosphere. This chemically inert element is colourless, odorless and harmless It has a larger and heavier molecule than air. Heat transfer occurs at a lower rate across materials of low thermal conductivity. Heat loss by conduction occurs because heat always moves toward cooler temperatures. Gas being more dense than air, slows the flow of building heat to the outside in winter and reduces the outside heat that can enter in the summer

Arris
Removing sharp edges on glass usually with a wet or dry belt, stone or machine. This is the minimum edge required on glass before furnacing.

Aspect Ratio
The ratio of the longer side of a panel to its shorter side

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

Autoclave
A chamber where high pressure and heat create bonding between the glass and interlayer producing a laminated glass product.

Balustrade
A framed or unframed barrier between handrail and floor level, required to protect difference in level of 1 metre or more.

Bead
A strip of timber, aluminium or other suitable material secured to the rebate to secure the glass in place. Also known as a glazing bead.

Bevel
A decorative edge on glass. A process of grinding and polishing a sloped angle on the face of the glass.

Blisters
Bubbles or gaseous inclusions in the glass. Small bubbles less than 2mm in diameter are referred to as seeds.

Bow
A curve or bend from flatness in glass.

Breather Tube Units
A very small capillary tube factory placed in the unit cavity to accommodate pressure differences for units being installed at high altitudes. These tubes must be sealed on the job site before installation.

Brewster’s Fringes
A rainbow effect, sometimes seen in IGU’s caused by the light refraction from identical thicknesses of glass.

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

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

CAD
The use of a computer to produce graphics, with a computer aided design program.

Cantilevered Balustrade
A glass 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 loads directly back to its fixing point.

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

Cerium Oxide
A substance used for polishing glass.

Chip
A small piece of glass which has become detached from the original glass edge.

Cladding Glass
Toughened or Heat strengthened glass painted or silk screened using ceramic paint.

CNC Processing
Computer Numeric Control. Machinery that enables the processing of sophisticated shapes in glass.

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

Conduction
The process by which heat is directly transmitted through material of a substance when there is a difference of temperature. E.G. when the handle of a pot on the stove gets warm, the heat is being conducted from the bottom of the pot all the way to the handle.

Convection
Convection heat transfer is heat flow via air movement. E.G. when a hair dryer is tuned on and the hot air is projected from the end of the hair dryer.

Countersunk Hole
A hole which is ground out at the surface, so that when the bolt or fixings are inserted, the screw head is level with the surface of the glass panel.

C.T.S
Abbreviation for Cut-to-size glass.

Cullet
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.

Curtain Wall
A non load-bearing wall of metal sections, glass and infill panels. Used in modern high rise office buildings, a great advantage is that natural light can penetrate deeper within the building.

Cut-out
A section of the glass panel is removed.

Daylight Size
The total area of a window opening that admits daylight.

Deflection
The bending movement at the centre of a glass panel, perpendicular to the plane of the glass surface under load.

Delamination
When the glass panels of laminated glass losses the bond with the interlayer.

Desiccant (silica Gel)
Molecular sieve or Silica Gel is placed in the cavity of an insulated glass unit to remove any moisture in the unit.

Design Wind Pressure
The pressure a product is designed to withstand.

Diffused Glass
Glass used in picture framing to avoid reflections and glare.

Direct Transmittance
The 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 pre-vent 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.

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

Double Glazing
Two panels of glass, separated by an air space, to improve insulation against heat transfer and/or sound transmittance.

Dry Glazing
This term is used to describe the glazing of single glass or insulating glass in the support-ing frame without wet sealants using preformed and extruded materials such as glazing gaskets and wedges.

Dual Seal
Insulation glass unit manufactured with primary seal and a secondary seal for maximum protection against moisture vapour transmission.

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

Edge Cover
The distance between the edge of the glass and the sight line.

Edge Work
Processing on the edge of flat or shaped glass.

Emissivity
The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation.

Faceted Glazing
Panels of glass installed vertically at an angle to each other to form a radius window.

Finger Slots
A finger grip for sliding glass panels produced by grinding a slot into the surface of the glass.

Finished Size
The finished size of a glass panel after cutting and processing is complete.

Fins
A panel of glass fastened to provide lateral support, located 90 degrees to the glazed surface.

Fire-Rated Glass
Glass that resists the penetration of flames and/or smoke for a period of time.

Flat Grind Edge
The edge of the glass is machine grinded where the edges are slightly arrised without a final polish.

Float Glass
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.

Gaseous Inclusions
Bubbles in glass.

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

Georgian Wired Glass
Georgian wire cast is produced the same as patterned glass. During the manufacturing process a 13mm welded steel wired mesh is added before the molten glass passes through the roller process. This is a B grade safety glass.

Girth
Perimeter measurement of a bend or curve.

Glass Flooring
Panel of three or more layers of annealed or toughened glass manufactured with interlayers and a non-slip coating in the upper surface.

Glazing
The installation of glass in prepared openings in windows, door panels and/or partitions.

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, giving a random pattern.

Handrail
A horizontal or sloped railing for support on stairwells and balustrades.

Hard Coat
Coating applied to glass during the manufacture whereby it is fused to the glass in the form of a pyrolytic coating. It can be cut and toughened and is very durable.

Heat Absorbing Glass
A glass whose solar transmittance is reduces by adding various colouring agents to the molten glass; the most common colours are bronze, grey and green.

Heat Gain and Heat Loss
Heat gain occurs in summer, where the exterior temperature is above the interior temperature and the heat flows inward. Heat Loss occurs in winter, where the interior temperature is warmer than the exterior temperature and heat flows out-ward. This is measured by U Value.

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

Heat Strengthened Glass
Heat strengthened glass is produced in the same manner as toughened glass except that the cooling process is slower. Heat strengthened glass is twice as strong as annealed glass. Heat strengthened is not a safety glass, but can be laminated to meet requirements.

Hermetically Sealed
Insulated glass units are hermetically sealed, made airtight.

Inclusion
A crystalline or non-crystalline particle trapped in glass.

Insulation Glass unit (IGU)
Two panels of glass, separated by an air space, to improve insulation against heat transfer and/or sound transmittance.

Interlayer
Plastic material used in the manufacture of laminated glass to bond the glass together.

Laminated Glass
Two or more sheets of glass permanently bonded together by a plastic interlayer material. Laminated glass will crack and break under sufficient impact, but the glass will tend to ad-here to the plastic interlayer instead of falling apart.

Light Transmission
Percentage of visible light passing directly through the glass.

Louvre
A window unit glazed with blades of glass or other material over lapping each other when in the close position.

Low Emissivity Glass (Low E)
The E in Low E refers to emissivity. This is the measure of materials ability to radiate energy. A material with low emissivity absorbs and radiates infrared energy poorly which is the key factor in reducing heat transfer.

Low Iron Glass
Manufactured removing a large proportion of the iron content and is extremely clear and transmits a high percentage of visible light.

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.

Manifestation
Marking of glass to minimise the potential for human impact and injury by making the glass more visible.

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.

Mirror
Glass silvered on one side with reflective properties.

Mitre Edge
Straight line edging machines produce mitred edges to an angle of up to 45 degrees with ground or polished edge.

Modesty panels
A panel of toughened shower screen glass silk screened or acid etched and sealed with a decorative pattern to give discrete curtain effect.

Monolithic Glass
A single panel of glass.

Mullion
A vertical framing member.

Newton Rings
A visual effected created when the centre of the glass panel is an insulated glass unit come so close as to touch each other. It will appear as a circular rainbow effect in the centre of the unit. This may indicate that the spacer width is too small, the result of temperature related pressure changes or improper pressure equalisation.

Nickel Sulphide Inclusions (NIS)
Minute particles of nickel and sulphur present in the raw material of glass which under heat, form into crystals and are in rare cases can cause spontaneous breakage.

Opaque
Denoting a solid colour with little if any light transmission.

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 in one or both sides. Used for diffusing light, privacy, bathrooms and decorative glazing. Also called figured rolled or obscure glass.

Polished Wired Glass
A clear glass that has been polished on both surfaces with a wire mesh embedded into it.

Poly vinyl Butyral (PVB) Interlayer
An extremely tough, resilient plastic film used to bond glass together to produce laminated safety glass.

Polyisobutylene
A butyl compound, which is the primary seal in a dual seal insulating glass unit and the key component is restricting moisture vapour transmission.

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

Pyrolitic
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 to form a metal oxide layer that fuses to the surface.

Reflective Glass
Reflective coating on glass to reduce heat and light transmission.

Roller wave
Corrugations or waviness 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.

R-Value
The thermal resistance of glazing system, the higher the R-Value, the less heat is transmitted.

Safety Glass
Glass which is treated to reduce injury to persons by the glass should it be broken by human contact. Laminate and toughened glass are A grade and Wired glass is rated B grade. These glass types satisfy the requirements of AS/NZS1288 for safety glazing.

Safety Backed Mirror
Mirror which has a sheet of organic material permanently bonded to one side so that the mirror holds together if broken.

Safety Wired Glass
Wire is completely embedded in the glass, to produce a B grade safety glass which meets the test requirements of the relevant safety glazing standards.

Screen printing
The application of ceramic paint to the surface of glass through a screen or mesh.

Security Glass
Thick laminated or multi-laminated glass designed to withstand various forms of violent attack.

Seeds
Small gaseous bubbles usually less than 2mm in size.

Serviceability Wind Pressure
Wind pressure conditions that meets glass in normal “in service” conditions. It is the wind pressure used for calculating deflection.

Setting Blocks
Generally a rectangular block of resilient non-absorbent material used to support glass in a rebate to prevent glass to frame contact. Used in pairs located at quarter points of the glass width.

Shading coefficient
The ratio of solar het gain through the glass relative to the through 3mm clear glass. The lower the number the better.

Sheet Glass
Clear glass manufactured by a drawing process. Sheet glass has natural fire finished surfaces, there is always distortion of vision and reflection.

Silica
Silicon dioxide, a mixture that is the main ingredient in the manufacture of glass. Sand is the most common form of silica used in glass making.

Slump glass
Glass that is heat treated to mould patterns or designs into the surface of glass.

Soft Coats
Coated glass where metal particles are 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
Tined and/or coated glass that reduces the amount of solar heat gain transmitted through the glass.

Solar direct transmittance
At normal incidence, the fraction of solar energy that is transmitted directly through the glazing.

Solar Heat Gain Coefficient (SHGC)
The proportion of solar radiation that is transferred through the glass at normal incidence. Solar heat gain includes directly transmitted solar heat and absorbed solar radiation which is then reradiated conducted or converted.

Solar Heat Transmission
The amount of solar energy transmitted directly through glass, compared with the solar total energy impinging on the exterior glass surface.

Solar reflectance
The percentage of visible light and solar energy reflected towards the exterior.

Spacer
A component of an insulated glass unit which separates the glass and includes a desiccant manufactured with additional sealants to prevent air and water penetration.

Spandrel Glass
Panels of an exterior wall to conceal structural columns, floors and shear walls located between vision areas of windows.

Stones
Crystalline inclusions embedded in glass.

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

Surface position
A number detonating which face a panel of glass or insulating glass unit the coating side or patterned side should face.

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

Temper (toughen)
Inducing predictable residual stresses in glass by controlled chilled 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.

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

Thermal Coefficient of expansions (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 when thermal stress meets or exceeds the breaking strength of the 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.

Tinted Glass
Tinted glass is produced by adding a colourant to the clear glass production run. This reduces unwanted heat gain and glare. The most common colours are bronze, grey, green and blue.

Toughened Glass
Toughened glass, also called heat tempered is an A grade toughened glass, which shatters into relatively harmless small pieces when broken. The additional stresses created in the tougheneing process increases its strength by 4 to 5 times, although the physical char-acteristics remain unchanged.

Toughened Laminated Safety Glass
Panels of toughened glass bonded together with an interlayer.

U Value
A measure of the rate of heat loss or gain through glazing due to the environmental differences between indoor and outdoor air. The lower the U-Value, the better the insulation.

Vented Inclusion
Crack in the glass surface caused by an inclusion.

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.

Visible Light Reflectance
The percentage of visible light within the solar spectrum that is reflected from the glass surface.

Visible Light Transmittance
The percentage of visible light within the solar spectrum that is transmitted through glass.

Warm-Edge
Refers to the type of spacer material used in the manufacture of insulated glass units to separate the panels of glass. If the material conducts less heat or cold than an aluminium spacer at the edge of the glass, it is said to be ‘warm edge’.

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

WHP Laminate
Windscreen High Performance Glass. An automotive quality laminate with high penetration resistance and high light transmission.

Wired Glass
During the manufacturing process a 13mm welded steel wired mesh is added before the molten glass passes through the roller process. This is a B grade safety glass.