A hollow, or negative container used in the process of casting to give its form to a substance placed within (wax for the bronze lost-wax process, or plaster, cement, resin loaded or not with slate, marble or bronze powder, etc.) and allowed to harden. Moulds can be made of plaster entirely, or in rubber with an outer plaster jacket (also called mother mould or casing). A one piece mould that must be destroyed to get the cast out is called a waste mould. A mould consisting of two or more separable pieces is called a piece mould. Often a sculptor will see his finished bronze sculpture through the making of two such negative moulds either himself or at the foundry. A first one to produce the mould in which the wax positive is poured. A second one built in (core) and around the wax positive and its sprue and gates, from which the wax is lost by firing in a kiln, and which is hacked off to reveal the rough cast bronze from which the sprue and gates will have to be removed. Metal casting is done by sand casting in which the negative, containing a mould and a positive core - allowing the final piece to be hollow - are made of foundry sand.