Glass Terminology

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Glass Terminology

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Definitions for a range of commonly used terms

These definitions have been compiled from a variety of industry sources and are meant to assist in becoming familiar with a range of terms used in our industry. These definitions are not designed to have any legal significance or consequences.

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Annealing
The process of preventing objectionable stresses in sheet, float, or rolled glass during manufacture by controlled cooling. Re-annealing is the process of removing objectionable stresses in glass by re-heating to a suitable temperature followed by cooling.

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Bead
A sealant after application in a joint irrespective of the method of application, such as caulking bead, glazing bead, etc. Also a molding or stop used to hold glass or panels in position.

Bent Glass
Flat glass that has been shaped while hot into cylindrical or other curved shapes.

Bite
The dimension by which the edge of a glass product is engaged into the glazing channel.

Block
Rectangular, curved sections of neoprene or other approved material used to position the glass in the glazing channel.

Bullet-Resisting Glass
A multiple lamination of glass with tough clear sheet plastic, usually of at least 1 3/16 inches thick overall, which is designed to stop bullets from ordinary firearms other than high-powered rifles.

Butt Glazing
Installing glass products where the vertical glass edges are without structural supporting mullions.

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Channel Glazing
Installing and sealing glass products into U-shaped glazing channels using removable stops.

Chemically-Strengthened Glass
Glass which has undergone ion-exchange to produce a comprehensive stress layer.

Cullet
Broken glass, excess glass from a previous melt, or edges trimmed off when cutting glass to size. Cullet, in some regular proportion, is an essential ingredient in the raw batch charge in glassmaking in that it facilitates melting.

Curtainwall
An exterior building wall which carries no roof or floor loads and consists entirely or principally of metal or a combination or metal, glass and other surfacing materials supported by a metal framework. There are two basic types:

Custom:
Walls designed specifically for one project and using parts and details specially made for this purpose.

Standard:
Walls made up principally of parts and details standardized by their manufacturer and assembled in accordance with either the architect's design or the manufacturer's stock patterns.

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Dead Load
Load force due to glass weight.

Desiccant
An extremely porous crystalline substance used to absorb moisture from within the sealed air space of an insulating glass unit.

Double Glazed Windows
A common term for insulating glass units, which feature either air or a safe, colorless, odorless gas tightly sealed between two panes of glass. For increased energy efficiency, one or both panes can be treated with a low-E coating.

Double Strength
In float glass, approximately 1/8-inch thick.

Dry Glazing
A method of securing glass in a frame by use of a dry, preformed resilient gasket, without the use of a compound.

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Edge Clearance
Nominal spacing between the edge of the surface of the glass product and the glazing channel base.

Edging
Grinding the edge of flat glass to a desired shape or finish.

Emissivity
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, essentialy, to reradiate absorbed energy (heat).

Exterior Glazed
glass set from the exterior of the building.

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Flat Glass
A general term that embraces float glass and various forms of rolled glass (as contrasted with fiber glass, containers, etc.)

Float Glass
Glass drawn over a bath of molten tin to attain a fire polish.

Fully-Tempered Glass
Glass that has been tempered to a high degree. Specified by ASTM C 1048 (Kind FT) as having a surface compression of not less than 10,000 pounds per square inch (psi) or an edge compression of not less than 9,200 psi. Fully tempered glass, if broken, will disintegrate into many small pieces (dice) which are more or less cubical. Fully tempered glass is four to five times stronger than annealed glass of the same thickness.

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Gasket
Preformed shapes, such as strips, grommets, etc., of rubber or rubber-like composition, used to fill and seal a joint or opening either alone or in conjunction with a supplemental application of a sealant.

Glass
An inorganic product of fusion which has cooled to a rigid condition without crystallizing. It is typically hard and brittle and has a coinchoidal fracture. It may be colorless or colored, and transparent to opaque. Masses or bodies of glass may be made colored, translucent, or opaque by the presence of dissolved, amorphous, or crystalline material.

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Heat-Absorbing Glass
Glass for intercepting appreciable portions of radiant energy, especially solar energy, in specific transmittance values as defined in ASTM C 1036. It is obtainable as float and patterned glass.

Heat-Resisting Glass
Glass able to withstand high thermal shock, generally because of low coefficient of expansion.

Heat-Strengthened Glass
Glass that has been heat-treated to a state less than that of fully tempered glass. Specified by ASTM 1048 (Kind HS) as having a surface compression of not less than 3,500 pounds per square inch (psi) or greater than 10,000 psi or an edge compression of not less than 5,500 psi. Heat-strengthened glass is approximately two times as strong as annealed glass of the same thickness and has a much increased thermal endurance. Heat-strengthened glass is not considered a safety glass and will not completely dice as will fully tempered glass.

Heat-Treated
Term sometimes used for both fully-tempered glass and heat-strengthened glass.0

Hermetically Sealed Unit
An insulating glass unit made up of two lites of glass, separated by a spacer, or equivalent product (at the full perimeter), which is filled with a moisture absorbing material. The unit is then completely sealed, creating a moisture-free, clean, dead-air space.

High-Transmission Glass
Glass which transmits an exceptionally high percentage of visible light.

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Insulating Glass
Insulating glass refers to two pieces of glass spaced apart and hermetically sealed to forma a single-glazed unit with an air space between. Heat transmission through this type of glass may be as low as half that without such an air space. It is also called Double Glazing.

Interior Glazed
Glass set from the interior of the building.

Interlayer
A layer of standard or polycarbonate-compatible polyvinyl butyral or of urethane, used to bind two or more pieces of glass or glass and polycarbonate sheets into a laminated unit.

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Laminate
A composite unit of glass and interlayer material.

Live Load
Load force due to weight of non-permanent attachments such as people, glazing rigs, washing rigs.

Low-E or Low-Emissivity
Is to have a low rate of emitting (radiating) absorbed radiant energy. The radiant energy (heat) is, in effect, reradiated toward its source.

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Monolithic
A glazing assembly construction consisting of only one lite or pane of glass, polycarbonate, acrylic, or plastic.

Mullion
An intermediate connecting member used to "marry" two or more windows or patio doors together in a single rough opening without sacrificing air or watertight performance. a mullion also can give added strength to the connection for structural stability.

Muntins
A decorative design in cut-ups of glass lites. Examples:

1) Painted muntin grids applied to an interior lite of glass in a sealed insulating glass unit to simulate cut-ups of glass lites either in colonial or diamond patterns.
2) Use of aluminum muntin bar between lites of glass in a sealed insulating glass unit to simulate glass cut-ups.
3) Use of actual vertical and horizontal bars to divide a window into smaller lites of glass. The bars are termed muntin bars.

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Patterned Glass
(also Rolled or Rough Rolled Glass) One type of rolled glass having a pattern impressed on one or both sides. Used extensively for light control and decorative glazing.

Polished Wired Glass
Wired glass that has been ground and polished on both surfaces.

Priming
Sealing of a porous surface so that compound will not stain, lose elasticity, shrink excessively, etc. because of loss of oil or vehicle into the surround. A sealant primer or surface conditioner may be used to promote adhesion of a curing type sealant to certain surfaces.

Processed Glass
Glass in which the surface has been altered by etching, sandblasting, chipping, grinding, ceramic-enameling, etc., to change its light diffusion or to give decorative effects. Either or both surfaces may be so treated. Also glass which has been further treated (edge work, tempered, stained, etc.) after forming.

Pyrolytic Coating
A coating applied during the manufacturing of the glass itself. Because they are actually part of the glass sheet, pyrolytic or "hard coat" surfaces are very durable and require no special handling.

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R-value
Denotes a material's ability to act as an insulator. The higher the R-value, the less heat transference; it is the reciprocal of the U-value and can be expressed as R = 1/U.

Reflective Glass
Glass with a reflective surface film to reduce heat and light transmission.

Rolled Glass
Glass formed by rolling, including patterned and wired glass. As the glass is drawn horizontally from the tank, figured, engraved, etched, machine rolls impress a pattern on the surface of the glass, varying from almost smooth to deeply marked geometric, fluted, or random overall designs. It is made in 1/8-inch to 3/8-inch thicknesses.

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Sandblasted Finish
A surface treatment for flat glass obtained by spraying the glass with hard particles so as to clip out and roughen one or both surfaces of the glass. The effect is to increase obscurity and diffusion, but can make the glass fragile and hard to clean.

Sash
The frame, including muntin bars when used, and including the rabbets to receive lites of glass, either with or without removable stops, and designed either for face glazing or channel glazing.

Sealant
Compound used to fill and seal a joint or opening, as contrasted to a sealer which is a liquid used to seal a porous surface.

Shading Coefficient
Is the ratio of solar heat gain passing through a glazing system to the solar heat gain that occurs under the same conditions if the window were made of clear, unshaded double strength window glass. The lower the number, the better solar shading qualities of the glazing system.

Shelf Life
Used in the glazing and sealant business as referring to the length of time a product may be stored before beginning to lose its effectiveness. Manufacturers usually state the shelf life and the necessary storage conditions on the package.

Sight Line
Imaginary line around the perimeter of lites or panels corresponding to the top edge of stationary and removable stops, and the line to which sealants contacting the lites or panels are sometimes finished off.

Single Glazing
A single pane of glass.

Sloped Glazing
Any glass installation at a slope of 15º or more from vertical.

Spacers
(Shims) Small blocks of composition, neoprene, etc., placed on each side of lites or panels to center them in the channel and maintain uniform width of sealant beads. Prevent excessive sealant distortion.

Spandrel
That portion of the exterior wall of a multi-story commercial building that covers the area below the sill of the vision glass installation and the area above the head of the glass installation below.

Spandrel Glass
Heat-strengthened float glass with a colored-ceramic coating adhered to the back by a heat-fusing process. it has double the strength of annealed glass of the same size and thickness, enabling it to withstand greater uniform loads and thermal stresses. Spandrel glass cannot be re-cut after heat strengthening. It is used as fixed opaque colored glass on buildings in front of floor slabs and columns. It is available in a wide array of colors.

Sputter Coating
A micro-thin metallic oxide coating vacuum-deposited on the surface of glass after manufacturing. Sputter coatings are vulnerable to moisture and abrasion and must be enclosed in sealed insulating window units.

Stain
Attack of a glass surfaceby water or other solutions involving:

a. Leaching of sodium ions to the surface of the glass.
b. An increase in pH on the glass surface.
c. The breaking of silica bonds in the glass structure.

If this process advances to c, the glass willhave a blotched, streaked, cloudy appearance and cannot be restored to pristine condition short of grinding and polishing the damage away, a process that is generally more expensive than simply replacing the glass.

Stones
Crystalline contaminations in the glass, usually pieces of undissolved or crystallized silica, bits of refractory, or crystals due to devitrification. Stones are detrimental to appearance and may seriously weaken the glass, particularly if present in highly stressed areas.

Structural Glazing
Is based on the use of a sealant not only as a weather seal but also for the structural transfer of loads from the glazing panel to its perimeter support system. Only certain specific sealant formulations are suitable for this purpose.

Structural Glazing Gaskets
Cured elastometric channel-shaped extrusions used in place of a conventional sash to install glass products onto structurally supporting sub-frames, with the pressure of sealing exerted by the insertion of separate lockstrip wedging splines.

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Tempered Glass
Glass that has been rapidly cooled from near the softening point, under rigorous control, to increase its mechanical and thermal endurance. Fully tempered glass always "dices" into a multitude of smal particles.

Tinted Glass
Glass with a material added to give the glass a light and/or heat reducing capability and color.

Total Solar Absorption
The percent of incident solar radiation that is absorbed by a glazing system.

Total Solar Reflectance
The percent of solar radiation that is reflected by a glazing system.

Total Solar Transmittance
The percent of incident solar radiation that directly passes through a glazing system.

Transmittance
The ability of the glass to transmit solar energy in the visible light, the ultraviolet, and the infrared ranges, centrally measured in percentages of each other.

Triple Glazing
Windows that are made of three panes of glass with air space between the lites, and may be filled with argon or other gases for increased energy efficiency.