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Dictionary of most important terms used in Glass Industry

Annealed Glass

Glass that does not undergo the process of toughening, lamination or heat strengthening. Also known as 'normal' glass and most commonly used for flat glass.


A barrier or form of guarding, generally waist-high, which protects people from falling where there is a change in floor level, for example stairs and balconies.


A strip of wood, metal or other suitable material attached to the glazing surround to retain the glass.

Transparent float glass with a consistent colour throughout its depth.

Bolted Glass Assemblies / Assembly Systems

Structural bolted glazing systems incorporating fixed or articulated bolts.


A form of distortion in toughened and heat strengthened glass, inherent to the manufacturing process.

Bullet-Resistant Glazing

Security glazing affording a defined resistance against the firing of specified weapons and ammunition

Blown Glass

The shaping of glass by blowing air through a hollow rod into the center of a molten glass gather.

Curtain Walling

Non-load bearing, typically aluminium, façade cladding system, forming an integral part of a building's envelope.

Cast Glass

Glass produced by 'casting', by pouring molten glass into a mould or by heating glass already contained in the mould until the glass melts and assumes the shape of the mould.

Cut Glass

Glass that is decorated by using grinding stones that are worked wet to cut designs onto the glass.

Transparent glass with an almost colourless and neutral appearance.


The reorientation of daylight by means of systems incorporating reflective and adjustable surfaces or grilles. Daylighting systems redirect natural light, distributing diffused light in a room space and prevent strong areas of glare.

Double Glazing

Double glass panes divided by an inert gas space, the objective being thermal/acoustic insulation.

Energy Balance

The difference between the amount of heat gain and heat loss through glazing. Also known as the "Effective U-Value".


Emissivity is a surface characteristic of a material. It is the relative ability of a surface to absorb and emit energy in the form of radiation. Low-emissivity (Low E) coatings reduce the surface emissivity of the glass. The coatings are mainly transparent over the visible wave.

Energy Absorptance (A)

The percentage of solar radiant heat energy absorbed and re-emitted externally and internally by the glass.

Energy Reflectance (RE)

The percentage of solar radiant heat energy reflected by glazing.


The heat transfer coefficient because of temperature differential between outdoor and indoor. Expressed in terms of watts of energy transfer per square meter per degree Celsius or degree Kelvin.

Energy Transmittance (T)

Percentage of solar energy flow transmitted directly through the glass.

Enameled Glass

Opaque glass colors, which are actually glass powders, that are melted onto a glass surface..

Face of the building.


Any area within the building, that lets in light. Includes windows, glass doors, glass block walls and skylights.

Fibre Glass

Very fine strands of glass used in the form of glass wool.

Flat Glass

A commonly used terminology to indicate sheet glass, float glass and other forms of rolled/plate glass where the shape of the glass is flat.

Float Glass

Produced when molten glass is floated on a bath of molted tin to form a continuous glass ribbon. Also a type of flat glass.


Ground glass, ranging in a variety of sizes from fine powder to gravel-like size. Sometimes used for painting effects and can be fused or cast.

Glazing Materials

The materials required for the glazing of glass products such as glazing compounds, tapes, sealants and gaskets.


The process of securing glass into provisions made in buildings, especially doors, windows and partitions.

G-Value (g)

Abbreviation or symbol for Solar Factor according to EN 410, formerly abbreviated to SF or TT.


A ball of molten glass taken from a pot or furnace on the end of a hollow blow rod.


Colourless, tinted, transparent or opaque, an inorganic product of fusion cooled without crystallizing. Referred by the name 'monolithic glass'. Hard and brittle with a conchoidal fracture.

Glass which has been heat-treated in order to increase its mechanical strength and resistance to thermal breakage. It has fracture characteristics similar to that of ordinary annealed glass and is not classed as a safety glass to BS 6206.

Heat-Treated / Heat Treatment

A generic term for glass that has been heat-strengthened or thermally toughened in order to increase its mechanical strength and resistance to thermal breakage.

Insulating Glass Unit (IGU)

An assembly comprising at least two panes of glass, separated by one or more spaces, hermetically sealed along the periphery.


Insulated chamber for heating and cooling glass or ceramics.


Glass that is altered, fused, shaped, slumped, or textured by the heat of a kiln.

Laminated Glass / Laminate / Laminating

Two or more sheets of annealed or heat treated glass are separated by one or more plastic interlayers (normally PVB) and subjected to heat and pressure, in order to ensure perfect adhesion between constituent elements.

Light Reflectance (LRe)

The proportion of the visible spectrum that is reflected by the glass.

Light Transmittance (LT)

The proportion of the visible spectrum that is transmitted through the glass.

Low Iron

Referring to extra clear glass, which has a reduced iron oxide content in order to lessen the green tinge inherent to ordinary clear float glass.

LSG Ratio

Light to Solar Gain (LSG) is the ratio of the Visible Light Transmittance (VLT) and Solar Heat Gain Coefficient (SHGC) of a glass. In absolute percentage terms, a ratio greater than 1 signifies that the daylight passing through the glass is more than the sun’s direct heat passing through it.

Produced by depositing and baking lacquer coating on one side of clear glass.

Low Emissivity or low-E Glass

Glass with a special thin-film metallic or oxide coating which allows the passage of short-wave solar energy into a building but prevents long-wave energy produced by heating systems and lighting from escaping outside. Allows light to enter while also providing thermal insulation.

Monolithic Glass

A single sheet of flat glass that could be annealed/toughened/heat strengthened.

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

Maximum Thickness

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

Minimum Thickness

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

Nominal Thickness

Numeric designation to indicate the approximate thickness of glass.

Outdoor light reflectance (%):

Outdoor light reflectance, or daylight reflectance, is the percentage of light striking the glazing that is reflected back. It indicates the degree to which the glazing appears like a mirror from the outside.

Pyrolytic Coating / Coated

A specialist metallic coating is applied to the glass "online" during the float glass manufacturing process. The high temperatures involved resulting the metallic oxides fusing into the surface of the glass through pyrolysis and effectively forming part of the glass. See SGG Antelio Plus, SGG Reflectasol, SGG Bioclean.


A ready-to-be glazed single piece of glass or plastic glazing sheet material in a finished size.

Patterned Glass

Rolled Glass with patterns. Can be on either or both sides of the glass.

Reflective Coating / Coated

A metallic coating is applied to one side of the glass in order to significantly increase the amount of reflection by the glass of both the visible and infra-red (light and heat) range of the electromagnetic spectrum.

Rolled Glass

Translucent glass with 50-80% light transmission. Used where transparency of the glass sheet is not important or desired.

Structural Glazing

Glass acting as a structural support to other parts of the building structure, for example glass fins. It can also refer to glass that is fixed by means of bolted connectors where the glass is not acting as a structural element.

Self-Cleaning / Self-Cleaning Glass

Glass with a photocatalytic and hydrophilic coating. The coating harnesses the dual-action of UV light and rain (or water) to break down organic dirt and reduce the adherence of mineral material. The glass stays cleaner for longer and is easier to clean.

Safety Glass

Glass which must have passed an impact test (BS 6206:1981) and either must not break or must break safely.

Safety Critical Locations

Identified by BS 6262 part 4 and defined as glazed sections of a door, wall or other part of a building most likely to be subject to accidental human impact.

Solar Heat Gain

Solar radiant heat, transmitted or re-emitted by glazing into a building, contributing to the build-up of heat.

Safety Glass

Glass which does not disintegrate into sharp and potentially dangerous splinters when broken. May be produced by laminating or tempering.

Sheet Glass

A transparent flat glass with apparent glossy, fine finish but with waviness of surface.


A fenestration surface that has a slope less than 60 degrees from the horizontal plane.


Transmitting light but obscuring clear vision.

Glass that has been subjected to a controlled heating and cooling process, in order to significantly increase its resistance to mechanical and thermal stress. Through the thermal toughening process, the glass attains its safe-breakage characteristics.


A horizontal framing bar between glass panes. It can also be used to refer to a fanlight over a door.

Thermally Insulating Glazing

Double-glazed units provide thermal insulation.


Clear, permitting vision.

A float glass to which colourants are added during manufacturing, resulting in tinting and solar radiation absorption properties.


The heat transfer coefficient because of temperature differential between outdoor and indoor. Expressed in terms of watts of energy transfer per square meter per degree Celsius or degree Kelvin.

Unframed Glazing

Glazing with one or more edges unframed.

Visible light transmittance (%):

Visible transmittance, or daylight transmittance, is the percentage of visible light striking the glazing that will pass through. Visible transmittance values account for the eyes’ relative sensitivity to different wavelengths of light. Glazing with a high visible transmittance appears relatively clear and provides sufficient daylight and unaltered views; however, it tends to create glare. Glazing with low visible transmittance is best used in highly glare-sensitive conditions, but can create gloomy interiors under certain weather conditions and diminished views. It is unsuitable for many day-lighting applications since it does not provide enough light for typical visual tasks. While glazing can have a high visible transmittance, it does tend to obscure views, e.g., frosted or patterned glass.

Vertical Fenestration

Any type of fenestration other than skylights.

Wired Glass

Flat rolled glass reinforced with wire mesh and used especially for glass doors and roofing to prevent objects from smashing through the glass and also to hold pieces of broken glass together. Produced by continuously feeding wire mesh from a roller into the molten glass ribbon just before it undergoes cooling. Protects against break-in and fire spreading.




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