Glass Terms Glossary

Not too long ago, there was a post on the Etsy Forums asking people to please not "confuse the customer". And while I do believe that Google, Wikipedia, and a dictionary should answer most people's questions, it does bring up the fact that there are a lot of technical terms in any field, which are confusing to folks who are unfamiliar with the territory.

Since I work primarily with glass these days, I thought I would start a glossary of Glassworking Terms...that way, I can point folks to it, and hopefully contribute something to the collective education of the customer base!


Anneal
To reduce the stress in a piece of glass by controlling the rate of cooling. By allowing the glass to come to a uniform temperature and then cool at a uniform rate, the internal stresses are reduced. These stresses can cause a piece of glass to become brittle or even fracture.

Annealing point
The temperature at which the annealing process starts. This will vary depending on the type of glass, thickness, and other factors.

Annealing temperature/zone
The temperature or zone where the annealing occurs. The zone is the range where the glass converts from liquid to solid or vice versa.

Bail
The loop at the top of a piece of jewelry which allows it to be hung on a chain. May be wire, solid metal, glass, or another material. May be glued on after the glass is complete, or incorporated as part of the glass.

Base
The foundation piece of glass, onto which more glass is fused. For example, a piece may use a black base, and have multicolored pieces fused to the top, and may be capped with clear.

Bead Release
A liquid consisting of powdered ceramic material. Bead mandrels are dipped into it, and are then air dryed or flame dried. The release allows beads to be removed after they cool (otherwise the glass would stick to the metal.)

Billet
Bricks of glass which are melted for fusing larger projects.

Borosilicate
One of the types of glasses commonly used for lampworking. Sometimes jokingly referred to as "recreational" or "bong" glass, as it is the type of glass used for pipes. Has the lowest COE of commonly used glasses, making it very stable to work in a flame and less subject to sudden thermal shock. Pyrex is a common brand name.

Bubbles
Just what it sounds like. Small bubbles of air trapped between pieces of glass, or in a bead. Sometimes on purpose, sometimes not.

Burner
Another word for the torch used in lampworking.

Cabochon
A smooth piece of stone or fused glass used for jewelry making. Has no hole, usually has a flat side on the back. Can be glued to backings, or have a bail glued to it, or used in wire wrapping.

Cap/Capped
A sheet of glass fused over the top of another piece. Often used to refer to a clear cap put over other colors to add depth to a piece.

Casting
Filling a mold with melted glass or frit

COE (Coefficient of expansion)
A number which refers to how much and at what rate a given material expands and contracts when it is heated or cooled. It is important to use glasses of a compatible COE in any given project, or the difference in expansion/contraction will eventually tear the piece apart.

Combing
Drawing a pick or set of picks across hot glass inside a kiln.

Cold working
Any work done to a piece of glass when the glass is at room temperature, such as cutting, grinding, polishing, faceting.

Compatibility
See "COE". This is a measure of how well glasses will fuse with one another.

Crash cool
Speeding up the rate of cooling a kiln. Generally this involves opening the lid, but can also be done with an exhaust vent.

Devitrification
A whitish "bloom" that appears on glass as an undesirable effect of incorrectly firing.

Dichroic
Shiny, decorative glass created by applying metal oxides in a vacuum furnace. Dichroic coating can be applied to any substrate glass, and can be used in lampworking or fusing.

Draping
Heating glass to drape it over a form. (See also slumping.)

Fiber Board
Board used to insulate kilns, make molds, or create dams for molten glass.

Fiber Paper
Heat resistant substance used to prevent glass from sticking to itself or shelves. Can be fired between two pieces of glass to create a hole (it must stick out from between the glass so it can be removed after firing) or pre-fired to create a soft, drapable nonstick surface for draping molds.

Fire Polishing
Heating glass to the point the edges soften and the surface smooths out.

Float Glass
Clear glass, usually used for windows, made by making glass over a bed of molten tin.

Frit
Glass broken into fine pieces. Ranges from powder to 1/4" or larger chunks.

Full Fuse
The point where all the glass has been heated until it melts together to an even level.

Hand Rolled Glass
Glass made by ladling onto a table and then rolling it out by hand. Much rougher than float glass.

Iridescent Glass
Glass with a metallic coating, not to be confused with dichroic. Iridescent glass doesn't fuse to itself, and it is less likely to stick to a shelf when fused irid side down.

Kiln Wash
A powder mixed with water to paint onto molds and kiln shelves to prevent glass from sticking to them.

Lampworking
Also called torchworking. Shaping glass with an open flame, usually an oxygen/propane setup.

Machine Rolled Glass
Glass created by drawing molten glass through steel rollers.

Mandrel
Steel rods around which glass beads are made. Dipped into Bead Release to allow the glass to be removed after cooling.

Polariscope
A device using two polarized filters to identify stress in fused glass. My low-tech one is two polarized sunglass lenses and a flashlight. The only way to easily test for compatibility in unknown glass.

Pyrometer
A device for measure temperature.

Quenching
Dropping hot glass into water to cause it to break into pieces.

Ramp
The speed at which the kiln temperature is raised or lowered.

Rod
A long wand of glass, used primarily for torchworking.

Tack Fuse
Fusing pieces of glass just to the point where they stick together, preserving the texture of different pieces of glass.

Venting
Opening the kiln to allow fumes or heat to escape quickly.