General Glass Information / Glossary

About Glass & Crystal

Crystal refers to particularly clear, hard glass with superior ability to transmit and reflect light. Lead crystal, so named because it contains lead, and is familiar to many due to its traditional use in cut glass tableware. However, there are several types of crystal, many of which do not contain any lead.

Jade Glass is very hard, clear glass finished to a high polish. Its name comes from the jade green tint apparent when the glass is viewed from the side. This colour comes from the iron ore content in the silica used to produce the glass.

StarFire Crystal is the name given to lead and iron free, colourless glass, produced at extremely high temperatures. Its pure clarity is comparable to all but the finest optical crystal, and results in a beautiful sparkle on its polished edge.

Optical Crystal is extremely hard, clear and lead free. This permits specialized polishing to produce a surface that transmits light with little or no distortion, and which sparkles with diamond like brilliance when cut into facets. Its precise optic effects, developed for the scientific requirements of lens makers, also make it the finest engravable surface for artistic impression.

AzureLite (Teal) and Grey Glass are created by the addition of pigments that impart a uniform translucent colour to the glass. Although less brilliant than transparent glass, they provide a rich background to the frosted texture of sand-carved designs and create a dramatic visual effect.

A brief description of commonly used glass, technical and non-technical terms.

Antique Glass

Glass with an uneven surface texture and bubbles inside, produced using antique methods in order to obtain the appearance of glass made before the development of industrial processes. It may be drawn or produced from mouth-blown cylinders.

Art Glass

Cathedral, Opal and Rolled glass are different types of stained glass commonly used in most leaded glass projects. Applications usually are for door lights, window lights; free hanging sun-catchers, luminous panels; lampshades and other forms of art-works.

Architectural or Pattern Glass

Patterned glass is made with a rolled glass process. The semi-molten glass is squeezed between two metal rollers. The bottom roller is engraved with the negative of the potter. Thickness is controlled by adjustment of the gap between the rollers. The depth, size and shape of the patterns largely determine the magnitude and direction of reflection. Patterned glass usually transmits only slightly less light than clear glass. It can be used for a variety of applications: interior design and decorations, furniture, windows, etc.. Most architectural pattern glass is generally 4 mm thick, although certain patterns may be available in 3mm, 5mm, or 6mm, or greater thicknesses. Many of the available patterns may be tempered and most may be laminated.


The production, by abrasion, of a sloping edge on the glass sheet.

Bent Glass

Bent glass is produced in a horizontal mould by slowly heating the glass to approximately 600C, at which the glass softens sufficiently and takes the shape of the mould. The glass is then slowly cooled to avoid any internal stress. The mould itself plays a very important role in bent glass manufacturing because it determines the quality and angle of the curve.

Cast Glass

Glass produced by 'casting', in other words 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.


The production of a design in glass by cutting into the glass surface. Engraving methods include copper wheel engraving, diamond or tungsten point engraving, acid etching and sand blasting.

Flat Glass

All types of glass (rolled, float, plate, etc.) produced in a flat form, regardless of the method of production.

Float Process

A method for the production of high-quality sheet glass whereby a ribbon of molten glass is fed across a bath of heated liquid, usually molten tin, in a carefully controlled atmosphere. The process was developed by the UK firm Pilkington Brothers.


(1) The process of founding or melting the batch; (2) heating pieces of glass in a kiln or furnace until they bond; (3) heating enameled glasses until the enamel bonds with the surface of the object.

Fusing Glass-to-glass

Glasses of different compositions can be fused together for decorative purposes and also in the sealing of electrical, medical and industrial components. The fusion temperature for soda-lime glasses is generally between 760C and 820C. Particular attention must be paid to the thermal expansion coefficients of different glass types.


A furnace or oven for fusing, enameling and casting glass.

Laminated Glass

Laminated (or compound) glass consists of two or more sheets of glass with one or more viscous plastic layers "sandwiched" between the glass panes. The solid joining of the glasses takes place in a pressurized vessel called an autoclave. In the autoclave, under simultaneous heating of the already processed layers of glass and special plastic, lamination occurs. When laminated safety glass breaks, the pieces remain attached to the internal plastic layer and the glass remains transparent.


A form, normally made of wood or metal, used for shaping and/or decorating molten glass.

Opal Glass

Glass that resembles an opal, being translucent and white, with a grayish or bluish tint.

Plate Glass

Flat glass made by the casting or rolling of molten glass which is then mechanically ground and polished to produce a smooth and transparent sheet.

Rolled Glass

Rolled (or cast) glass is a translucent glass with 50-80% light transmission, depending on its thickness and type of surface. It is used where transparency of the glass sheet is not important or not desired. To produce rolled glass, molten glass pours from the melting tank over a refractory barrier (the "weir") and onto the machine slab where it flows under a refractory gate (the "tweel"), which regulates the volume of glass, and then between two water-cooled rollers. The distance between the rollers determines the thickness of the glass.

Safety Glass

Glass, which does not disintegrate into sharp and potentially dangerous splinters when it is broken. Safety glass may be produced by laminating (see "laminated glass") or by tempering (see "tempering").

Sandblasting Glass and Other Materials

A method for giving glass surfaces a matt finish either for decoration or to reduce transparency. The method was invented in 1870 by an American, Benjamin C. Tilghman, who is thought to have been inspired by the effect of sand being blown against windows on the American prairies. Compressed air forces the abrasive material through the nozzle of a sandblasting gun and onto the glass surface. Although sand can be used, more effective abrasives with less toxic effects are now available. Silicon carbide is commonly used, as is electro-corundum (aluminum oxide). The glass is normally placed inside a special cabinet with armholes, a viewing window and dust extraction facilities.

Tempering Glass

Special process of solidification of a glass sheet in order to make it particularly resistant to breakages. The process may be physical (thermal) or chemical. In the former, the glass sheet is heated to a temperature just below its softening point and then immediately cooled by special jets of cold-air. These harden the surface of the glass, giving the inside more time to cool. This allows the external layer to crystallize into a wider lattice while the inside solidifies with greater compression than in the crystal lattice. The result is a sheet of glass which is two or three times stronger than untempered glass and which, upon breakage, shatters into tiny pieces with blunt edges (the most common applications are for automotive glass). The chemical process, on the other hand, is based on the so-called ion-stuffing technique. Different chemical elements possess different ionic radii and therefore different densities. Hence, if glass containing sodium is cooled slowly in a salt bath of molten potassium, the sodium ions will migrate from the glass to the salt, while the potassium ions will move to the surface of the glass where, due to their wider radium, they create a denser and therefore stronger surface layer (of no less than 0.1 mm). Glass sheets which have been chemically tempered are five to eight times stronger than those which have not undergone any tempering process. (For more information, download our tempered glass information sheet, you will need Adobe Acrobat to view)

Useful Links

AFG Glass
Corning Museum of Glass
Guardian Industries
Saint Gobain Glass
PPG Industries
Stained Glass Quarterly