Temper (pottery)

A temper is a non-plastic material added to clay to prevent shrinkage and cracking during drying and firing of vessels made from the clay. Tempers may include:


 * Bone;
 * Chaff;
 * Charcoal;
 * Ground schist;
 * Wood ash;
 * Grit;
 * Sand or crushed sandstone;
 * Crushed limestone;
 * Crushed igneous rocks, such as volcanic rock, feldspar, or mica;
 * Grog;
 * Plant fiber;
 * Horse manure (dried and sifted);
 * Crushed mollusc shells (including fossilized) (see Shell tempering in the Mississippian culture); and
 * Freshwater sponge spicules.

Some clays used to make pottery do not require the addition of tempers. Pure kaolin clay does not require tempering. Some clays are self-tempered, that is, naturally contain enough mica, sand, or sponge spicules that they do not require additional tempering.