On completion of a clay model there may be a requirement to make a more permanent reproduction or series of reproductions and the techniques involved are mould making and casting. A mould is a negative impression of the original sculpture and can be made in one of many materials for example; plaster, liquid latex, silicone rubber or vinyl rubber and can be as simple as a one piece block or a complex multi-piece mould made of many connecting parts. The choice of moulding material is determined by many factors, the material the original is sculpted in, the quantity or material the reproductions are to be cast in and the size or level of detail of the sculpture.
Latex is air drying and most commonly used for casting plasters and cements, it is applied in layers to build up a desired thickness before receiving support in the form of plaster or fibreglass. Vinyl rubber (Vinamould) is a re-useable rubber which is heated to a liquid and poured over the sculpture where it cools back to its original flexible state, vinyl is a good material for small numbers of castings but unlike other mould making materials can be re-melted and formed into a new mould. Silicone is a highly accurate cold curing two part moulding material that allows the broadest range of casting materials and capable of casting high number of reproductions.
Mould making can be complex and employs different techniques to that of sculpting the original work but there are resources in the form of technical booklets and published titles dedicated to this field.