Resin casting is a method of plastic casting in which a mold is filled with a liquid synthetic resin, which then hardens. It is mainly used for small-scale production, such as industrial prototypes and dentistry. It can be done by amateur hobbyists with little initial investment, and is used in the production of collectible toys, models and figures, but also in the production of small-scale jewelry. The synthetic resin for such processes is a monomer for making a thermosetting plastic polymer. During the curing process, the liquid monomer polymerizes into the polymer, causing it to harden into a solid.