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Glass Kiln Firing Glossary

Annealing

The process of slow cooling heated glass through the annealing zone to prevent the presence of internal stress.


Annealing Point

The most efficient temperature at which to anneal a particular glass.


Annealing Zone

The temperature range starting at the softening point and ending at the strain point. Generally located between 1100℉ and 600℉ (593℃ and 316℃), depending on the chemical makeup of the particular glass.


Blank

A solid bottom layer of glass on which other pieces of glass are positioned prior to fusing.


Burn Out

The process of pre-firing a mold or material in a vented kiln to remove, with heat, any unwanted contaminants.


Casting

The process of pouring molten glass into a mold.


Coefficient of Expansion (COE)

The measured expansion of heated glass based on the percentage of change of a glass rod heated one degree centigrade.


Combing

An activity in which glass that is heated to a liquid state is manipulated by pulling or "combing" a blunt point through the surface. Also used in glass blowing.


Compatibility

The absence of stress when different glasses are fused together. Glass that have the same or similar COE's are said to be compatible.


Crucible

A high temperature, pot-shaped container used to melt glass in furnaces or kilns.


Devitrification

A crystalline growth that appears as a scum or matte finish on the surface of some glasses when heated to fusing temperatures.


Fiber Paper

A thin, blanket type of ceramic fiber used in fusing for molds and kiln shelf protection.


Fire Polish

Heating glass to the point where the surface has a glossy, wet appearance. A technique used to retain a shiny surface to glass after it has been ground or sandblasted.


Firing Profile

a.k.a. Firing Schedule - The entire collection of heating rates, set point temperatures and soak times associated with a particular firing.


Flash Glass

A sheet of glass composed of a base layer with a thin contrasting layer of another color flashed or fused to the surface.


Frit

Small granules of glass ranging from fine powder to rock-salt size.


Frit Casting

A process in which a mold filled with frit is heated to the point where the frit fuses into a solid mass.


Full Fuse

Melting two or more pieces of glass into one single piece of glass. At full fuse the surface is without texture.


Furniture

A collective term for the various posts and shelving used to support and separate the glass within the kiln chamber.


Fuse

The process of heat bonding glass together.


Glass Separator

A protective coating used to keep glass from sticking to the kiln floor and shelves.


Kiln Formed

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


Laminate

To heat bond glass to the point of just sticking together.


Lamp Work

Any glass working technique done using the direct flame of a torch.


Mold

Any form made of a refractory material in which glass can be shaped by slumping into or over.


Pate'-de-verre

A frit casting technique; a paste of frit is placed in a mold and heated to the point where the individual granules fuse into a solid mass.


Peep Hole

Small hole(s) in a kiln designed for viewing the contents of the kiln chamber.


Pyrometer

The pyrometer is a meter that indicates high temperatures. In order to work, a pyrometer must have a thermocouple (temperature sensor) connected to it.


Refractory

Any material that will not bend, warp, deform or explode at a specific high temperature.


Sagging

When heated glass starts to soften, it slumps and sags under its own weight.


Slump

A Technique used to form glass using a mold, heat and gravity.


Soak

Holding glass at a particular temperature for a given period of time.


Softening Point

A term used to express the exact point at which unsupported glass, when heated, starts to soften and bend.


Stone

Small impurities in glass, such as a particle of furnace material.


Strain Point

The lowest annealing temperature. Below the strain point any stress in glass is permanent.


Stress

A force creating tension and compression within glass that could cause unwanted breakage. Internal stress can be caused by poor annealing or fusing of incompatible glass.


Strike

When glass changes color during a heating cycle due to the oxidation atmosphere of the kiln.


Thermal Shock

Glass breakage caused by rapid or uneven heating or cooling.


Thermocouple

The temperature sensing probe of a pyrometer. It's inserted into the kiln chamber to measure temperature.