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Ceramic Kiln Firing Glossary

Bisque

A fired piece of unglazed clay.


Bisque Stain

Color (stain) that is applied to bisque and does not require firing.


China

High quality porcelain.


Collar

Section added to a kiln for additional height.


Cone (Pyrometric)

Used in a kiln, a pyrometric cone deforms when the proper heatwork is achieved. Various cones are made to either trigger mechanical shut off's (Dawson Kiln Sitter) or to act as a witness to kiln conditions.


Cone Holder

Needed for support by some pyrometric witness cones. While still a valid method of securing witness cones, Evenheat prefers the use of a "self-supporting" witness cone, which needs no cone holder.


Cratering

Broken bubbles in glazed surfaces. Usually indicates underfiring.


Crazing

Small hairline cracks in glazed surfaces.


Decal

A picture or design transferred to a finished glaze and fired.


Dry Footing

Removing glaze from the bottom of ware to eliminate stilting. Eliminates glaze from sticking to the shelf.


Element

High temperature coils inside the kiln that produce the heat.


Firing

Process of heating the ware inside a kiln until matured.


Furniture

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


Glaze

A thin, smooth coating of ground glass, suspended in a liquid, applied to bisque or greenware which produces a hard glass-like surface when fired.


Greenware

Unfired clay objects.


Heatwork

The combined measure of time and temperature. Both time or speed of the firing along with the final temperature determine the amount of heatwork accomplished. Pyrometric cones deform at particular heatwork values.


Kiln

An oven or furnace which produces very high temperatures.


Kiln Sitter

A mechanical device that shuts the kiln off when a small pyrometric cone receives the proper amount of heatwork.


Kiln Wash

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


Limit Timer

A back up device for the kiln sitter. The limit timer shuts the kiln off, using a timer motor, in the event of a kiln sitter failure.


Luster

An overglaze, when applied to a glazed surface, that produces a radiant and brilliant effect. For example : mother of pearl.


Maturity

When ware and glazes have reached their proper heatwork.


Mold

As a verb: to shape clay. As a noun: a plaster form that liquid clay slip is poured into to manufacture greenware.


Nesting

Greenware that can be stacked only during a low fire bisque firing.


One Fire

Glaze applied to greenware and fired once.


Over-Glaze

Any decoration that is applied over a glazed surface and fired.


Peepholes

Openings in the side of kilns for ventilation and visual inspection of the kiln during firing.


Pinholes

Small holes in the glazed surface of the ware after firing.


Porcelain

A clay body that requires a high fire to become vitreous.


Posts

Refractory material used to support shelves at different heights inside the kiln.


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

A high temperature material.


Shelves

Sometimes referred to as plates. Refractory slabs used to support ware inside the kiln. This enables the entire kiln to be utilized.


Silica (Flint)

Material used in making kiln wash. Silica sand is used for propping porcelain.


Slip

Liquid clay that is poured into molds to produce greenware.


Soaking

Holding the kiln temperature at a desired temperature. Is also referred to as "dwell" time.


Stilts

Single or multi-pointed supports that are used to keep the ware from having contact with the shelves during a glaze firing. This eliminates the ware from adhering to the shelves.


Stoneware

A high fired ceramic body which is vitreous, not translucent and usually made of native clays.


Thermal Shock

Ware that has cracked after removing it from the kiln. Usually caused by removing ware while it's too hot.


Thermocouple

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


Underglaze

Colored slip which is applied directly to the greenware.


Venting

Allowing moisture and gases to escape from the kiln during firing.


Vitreous

A hard, nonporous surface.