A mould is a hollow shape, or negative impression taken from a sculpture that has to be cast. It is into this mould that the casting material is poured or pressed. More simple forms, such as the human face can be made in a single mould. Other shapes may need two or more pieces. Moulds have traditionally been made out of clay, sand and plaster of Paris, but today the choice includes rubber, concrete and plastics.
by Theodore Spicer-Simson