The process of making a metal object by pouring molten metal into a refractory void, or hole, and allowing it to solidify. The refractory void is usually contained in a mould. A core is necessary if the cast metal object is to contain a hollow space. Methods of casting include the use of open face moulds, sand moulds, cire-perdue or lost-wax investment moulds, and piece moulds made of refractory material such as ceramic or stone fitted together. A piece of metal that has been cast is also called a casting.