Pottery Vocabulary

Bat - Any slab used as a base for throwing or hand-building clay: also applies to a trough used to dry slurry clay to the plastic state: usually made of plaster, press board, plywood, or other porous material.

Bisque, Biscuit –  Unglazed, but fired ware, usually accomplished in a low temperature firing prior to a glaze fire; also applies to unglazed ware fired high, as in porcelain bisque.

Body – A combination of natural clays and non-plastics, especially formulated to have certain workability and firing characteristics.

Burnishing – Polishing with a smooth stone or tool on leather-hard clay or slip to make a surface sheen; the surface will not stay shiny at temperatures above 2000 F (1100 C)

Casting – Process of forming shapes by pouring deflocculated liquid clay slip into plaster molds for repetitive production.

Centering – Pushing a mass of clay toward the center with the centrifugal motion of a potter’s wheel.

Ceramics – Art and science of forming objects from earth materials containing or combined with silica, produced with the aid of heat treatment at 1300 F (700 C) or more.

Clay- Earth materials formed by the decomposition of igneous rock; when combined with water, clay is plastic enough to be shaped: when subject to red heat or above, it becomes dense and rock-like.

Coiling, Coil Building – Age-old method of constructing hollow forms by rolling and attaching ropes of soft clay.

Cones – Pyrometric cones, Orton or Seger brand; pyramids made of clay and glaze constituents that bend at specific temperature. Cones are placed in the kiln during firing to indicate the final heat; they are classified by numbers coded to their softening point.

Engobe – A liquid clay slip colored with metallic earth oxides or glaze stains applied to wet or leather-hard ware for decoration. Engobe can be covered by glaze or used alone.

Extrusion – Forcing plastic clay through and auger or form, mechanically or by hand, to change its shape; can be solid or hollow.

Firing – Heating in a kiln to the required temperature for clay or glaze, at least to red heat, 1300 F (700 C). Bonfiring in a pit or on the ground.

Foot – Base or bottom of a piece.

Glaze – Glassy melted coating developed by chemicals and heat on a clay or metal surface. Glaze provides decoration and color, prevents some penetration of liquids or acids, and yields a matt or glossy, functional surface.

Greenware – Finished leather-hard or bone-dry clay pieces not yet fired; raw ware.

Grog – Crushed or ground-up fired clay, purchased commercially or made by the potter; used to reduce shrinkage, it yields texture; aids in even drying and firing.

Hand-Building – The process of forming pieces without the use of a potter’s wheel. Examples are pinching, coil building and slab building.

Kiln – Furnace for firing clay, slumping glass, or melting enamels; studio kilns can achieve temperatures up to 2500 F (1370 C). They can be fueled carbonaceously, organically, or electrically.

Kiln Furniture – Refractory slabs, posts, supports (called setters) for holding ware in the kiln, handmade or purchased.

Kiln Wash – Half clay, half silica, mixed with water to coat kiln shelves.

Leather-hard – Cheese-hard stage which clay reaches before being bone-dry; stiff enough to support itself, but still can be altered.

Luting – A method of putting together coils, slabs, or other clay forms in the wet or leather-hard stage by cross-hatching and moistening; the same as scoring.

Matt – Dull, non-reflective surface; in the case of glaze, due to deliberate composition or immature firing.

Mold – Usually a plaster form, single or multi-pieced, which will be used to reproduce any number of accurate copies of the original model in clay or plaster.

Pinching – Moving and shaping clay with the fingers.

Plaster – The mineral gypsum, with the chemical composition of calcium sulfate, used for clay/mold reproduction and as a work surface.

Plasticity – Workability; clay is the only mineral having real plasticity, meaning the ability to form into any shape, and to get progressively harder in the same shape on being fired to 1300 F (700 C) and above. Other materials, such as talc, can be said to have claylike plasticity.

Pottery – A loosely used term; often means earthenware or just any clay piece that has been fired.

Pressing – Forming plastic clay in a plaster mold or other form, by laying it against the mold face.

Resist – Wax, varnish, latex, or other substance applied in pattern on a clay or glaze surface to cover an area while the background is treated by another material or color.

Scoring – A cross-hatch and moistening method of putting together coils and slabs in the wet or leather-hard stage; the same as luting.

Sgraffito – A design scratched through one surface to another.

Shrinkage – Contraction of clays or bodies in drying and firing, caused by the loss of physical and chemical water and the achieving of molecular density.

Slab – Flat piece of clay from which shapes can be fabricated.

Slip – A suspension of ceramic materials in water; generally refers to casting slip for molds; can mean a liquid clay engobe for decorating or a glaze slip.

Slurry – Thick suspension of one or more ceramic materials in water; usually refers to slushy clay.

Throwing – The process of forming pieces on a revolving potter’s wheel from solid lumps of clay into hollow forms.

Trailing – A method of decorating with engobe or glaze squeezed out of a bulb from a small orifice or poured from a narrow lip.

Translucency – Ability to transmit scattered light, not quite transparent.

Transparent – Clear, like window glass; can be colored or colorless. Texture or decoration instantly shows through a transparent glaze.

Wedging – Kneading clay to expel air and make the mass homogeneous for hand processes.