Clay which has been fired and ground into fine granules, used as an ingredient in a clay body or as a base on which clay is worked or fired which allows the form to contract freely as it dries. It may also be used for molds and cores and for objects cast and modeled. When added to clay it raises its firing temperature and makes it more stable, but it can also alter its appearance. Sometimes sand is used as a substitute. Also see investment and pyrometer.