Clay glossary

Fire clay boxes of various shapes, in which ware is placed to protect it from contamination or flame impingement during firing.

A glaze is applied to ware within the kiln by throwing some salt onto the flames during firing, the ensuing vapour then reacts with the clay surface to form a sodium alumino-silicate glaze.

The formation of dull scum on the glaze surface, caused by gases present in the kiln atmosphere, or sulphates present in the body or in the kiln gases.

The settling out, on standing, of particles from suspension in a liquid. This can occur when a casting slip or glaze is left overnight.

The cutting or scratching through the outer colour or engobe, using a sgraffito tool, to expose the clay body underneath.

A decorating technique where the colour in paste form is forced by the means of a squeegee through a fine mesh and onto a clay surface.

The adhesion and densification of particles of a single compound on heating.

The suspension of a clay body in water, used for casting ware in moulds. Deflocculants are added to keep the clay in suspension.

To maintain a pre-arranged temperature in the kiln for a particular time.

The flaking, cracking or other disintegration of ceramics when subjected to sudden temperature changes.