Terra cotta slip has two purposes. First, it serves as a simple coating, like a glaze, for hand-built or wheel-made pieces of terra cotta pottery. A slip-coating is customarily made of the same clay as the piece to be covered; because of that, slip usually adheres more easily than a glaze of other chemical composition. Second, slip is uses to make plaster-casted dishes or other objects. Anyone interested in making pottery needs to know how to make a slip.