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Ceramic Glossary

Glossary: Here you will find definitions of terms used in the ceramic arts.

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A device operated with an air compressor used for spraying on colors, either in overall coverage or decorative form.

A method of applying color and wiping it back to accentuate the detailed surface.

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Banding Wheel
A turntable operated by hand, used for decorating purposes.

Generally an all over coat of color on bisque on top of which detailed decorating is done.

A plaster disk or slab for clay work.

Clay that has been fired but not glazed. Sometimes referred to as "biscuit."

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A clay form made from a mold. May also refer to plaster castings.

Casting Slip
A liquid clay used in the process of forming objects with molds. Also referred to as "slip."

Cavity (of a mold)
The inside section of a mold where the casting is formed. Ceramics: Clay forms which are fired in a kiln.

A term which usually refers to the bone china of England, but also is associated with vitreous white wares and porcelain.

Cleaning Greenware
The process by which mold seam lines and surface imperfections are removed from unfired clay objects.

Applications of ceramic color by brush, sponge, and spray which cover an entire area or a specific area of a piece.

Conditioned Brush
A brush lightly coated or dampened with a fluid to prepare it for the application of a specific type of color or medium. A brush lightly coated or dampened with a fluid to prepare it for the application of a specific type of color or medium.

Conditioning Coat (glaze or underglaze)
A thin coat of color that will soak into the greenware or bisque well.

Cone (pyrometric cone)
A mixture of ceramic materials that is designed to soften and bend when the proper mixture of time and temperature is reached in the interior of the kiln.

Cone Plaque
A small clay cone holder used when cones are placed on the shelf of the kiln.

Cone Temperature
The mixture of time and temperature at which the cone will bend.

Bubbles in the glaze finish which break.

Tiny cracks that appear in the fired glazed surface.

Glaze which pulls together and beads up, leaving bare spots of bisque. Also referred to as "separation."

Heavy metal used in producing red glazes and underglazes.

Clay forms which are fired in a kiln.

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The alkaline substance which is added in extremely small amounts to slip to make it more fluid without adding excessive amounts of water.

The process of dipping ware into glazes.

A technique of applying color which produces a feather-like effect using a dry brush and liquid colors.

The process by which glaze is removed from the bottom or foot of a clay object so it may be fired without stilting.

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Porous clay bodies which are fired to maturity at approx. 2000°F.

The heating coils of an electric kiln. (Tired or burned-out elements refer to elements which carry too little or no electrical current for producing heat).

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Fettling Lines (seam lines)
The ridges created on a casting where the mold comes together. They are usually removed during the cleaning process.

Gentle rubbing of the glazed surface to remove ridges.

The process by which ceramic ware is heated in a kiln to bring glaze or clay to maturity.

Fired Finish
A finish that must be fired to produce proper color and surface finish.

Fired Products (fired color products)
Products which must be fired.

Firing Chamber
The interior of a kiln in which the ceramic ware is fired (also referred to as a fire box).

Firing Cycle
A system of gradually raising and lowering the temperature of a kiln to properly fire ware.

Flowing Coats
An application of glaze applied with a fully-loaded brush so the color flows onto the surface of the ware.

A product that has been tested and determined to be safe for use on surfaces which come in contact with food or drink.

The base or the part of the piece of ceramic on which it rests.

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A fired glassy coating on a piece of ceramic.

Gloss (G)
A shiny, glass-like finish. Greenware: Unfired clay forms or shapes.

Grit Cloth
A rough scrubbing material used in the process of cleaning greenware.

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Hard Spot
An area on greenware or bisque surface that resists color application.

Hot Spot
A section of a kiln that fires to a hotter temperature than the rest of the kiln.

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The process of carving a design into a greenware surface.

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Keys (of a mold)
The series of notches and bumps carved in the excess plaster around the cavity of the mold to !nsure a proper fit.

The device in which clay and glazed c!ay objects are heated to maturity.

Kiln Furniture
The series of posts, stilts, and shelves on which the ceramic ware rests in order to take full advantage of the interior space of the kiln.

Kiln Sitter (automatic shut-off)
A device used with a pyrometric cone to shut off the kiln when conditions inside the kiln cause the cone to bend.

The refractory coating applied to the top of the kiln shelves to protect them from glaze drips.

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Lead Release
The amount of lead that is dissolved from the surface of a glaze which has been in contact with acid solutions.

Greenware that is taken from a mold and is allowed to become firm but still retains its wet look.

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Matte (M)
A soft finish with little or no shine.

Matured Bisque
A bisque that has been fired at the proper rate of heating and cooling to produce an even state of hardness throughout.

Mini Bars
Pyrometric cones used to measure the firing temperature of a kiln. They are shaped like bars rather than cone-shaped.

Mold Strap (mold bands)
Devices made of cloth, rubber, or metal used to tightly secure parts of a mold together during the pouring process.

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The procedure of stacking greenware in a kiln during the bisque firing.

Non-fired Finish
A color that is applied to bisque. These colors are never fired in a kiln.

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OK Dinnerware
A product that when applied and fired according to label directions is safe for use on surfaces that come in contact with food.

Opaque (O)
Color which does not allow other colors to show through.

One-Piece Mold
A mold that is made up of only one section or piece of plaster. Also referred to as an open-pour mold because of the lack of a pouring gate.

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Peep Holes (vent holes)
Small holes in the side of a kiln used for viewing shelf cones and ventilating the kiln during the firing process.

Pin Holes
Tiny holes in the final surface finish of a glaze or underglaze.

Refers to the ability of clay to be formed into a shape and retain it.

Posts (kiln)
Articles made of refractory material which support kiln shelves during firing.

Pouring Spare
The excess clay formed at the pouring hole of a mold during the casting process.

Pour Hole (pour gate)
A section at the opening of the mold used for pouring the slip into the mold cavity.

(1 ) A device of clay or refractory material used for supporting greenware (usually porcelain) during the firing process. (2) Term applied to the slight opening of the kiln cover during the first stages of the firing process, kiln prop. (3) Another word for kiln posts.

Pyrometric Cone
A small piece of clay compound that reacts to time and temperature used to indicate maturity of ceramic clays and glazes.

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Refractory Material
Substances that have a resistance to high temperatures.

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Seam Lines
Small lines on greenware produced where two sections of a mold are locked together during the pouring process. Also referred to as fettlings.

Semi-Matte (SM)
A satin-like surface which has a slight sheen to it.

Semi-Opaque (SO)
Colors which generally allow only dark colors to show through.

Semi-Transparent (ST)
Slightly colored and/or speckled colors which allow most colors to show through with only slight distortions.

See crawling.

Shelf Cone Temperature
The cone temperature that is fired on the shelf of a kiln. The amount of heating the ware actually receives.

See casting slip.

Soaking Cycle
A short cycle at the end of the regular firing cycle which maintains the level of heating in the kiln, and enhances many glaze finishes.

Spray Gun
See airbrush.

Usually refers to a natural sponge used for cleaning and decorating greenware. There are also synthetic sponges available for ceramics.

Unfired colors used for decorating.

Small shapes of bisque with metal or wire spurs used for supporting glazed greenware during firing.

A combination of clays which form a stone-like vitreous body during firing.

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Test Cone Plaque
See cone plaque.

Three-piece Mold
A mold that has three pieces.

Thermal Expansion
The expansion that occurs in glazes and clays when heated in a kiln.

Thermal Shock
Sudden changes which occur in a clay or glaze which causes damage, usually through sudden heating or cooling.

Transparent (T)
Clear base colors which are free from cloudiness or distortion.

Two-piece Mold
A mold that has two parts.

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A color which is usually applied to greenware and in most cases is covered with a glaze.

Not firing hot enough or long enough, or both.

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Usually refers to porcelain and stoneware that are fired at a high temperature. The clay begins to become glass-like in nature, although not necessarily waterproof.

Vent Holes
Small holes made by puncturing the wet greenware with a needle tool when two pieces of ware have been attached. These small holes allow the air and gases to escape during firing. Also refers to the peep holes in the side of the kiln.

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