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.
[1] Tempers may include: Some clays used to make pottery do not require the addition of tempers.
Pure kaolin clay does not require tempering.
[6] Some clays are self-tempered, that is, naturally contain enough mica, sand, or sponge spicules that they do not require additional tempering.
[14][13] Ceramic#Archaeology