Verrocchio's most famous sculptures are made in bronze which is a sort of metal. To make a bronze statue, Verrocchio made the statue in wax. Then plaster was put over the wax, and the wax was removed, leaving a mould. The metal was heated over a furnace until it melted and became molten (liquid). The molten metal was poured into the mould and slowly allowed to cool. When the plaster was chipped away, the bronze statue was inside. The statue then needed to be finished and polished.