Release agent

A substance applied to the inside surfaces and seams of a mold to prevent the casting from adhering to the mold; also variously known as a separator, parting agent, or parting compound. A release agent for casting plaster in a mold may be a thin clay slip, or several applications of a soft liquid soap, petroleum jelly, or a thin oil. To permit clay to separate from a mold, apply either powdered chalk or talc as a release agent.