A traditional method of making casts, which is still practised in some places today, uses a mould made entirely of plaster of Paris. Also, in the 19th century, gelatine moulds were sometimes used.
More modern methods employ such materials as silicone rubber and polyurethane.
Most of the casts to be seen in the Ashmolean Museum Cast Gallery were made using the traditional plaster method, which is a skilled process requiring much experience. In Paris, for example, an apprenticeship of six years must be served in order to become a cast maker.