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The traditional way of making hollow works is the 'lost wax', or cire perdu process. This process usually involves many complicated steps, but the simplest procedure is to coat the interior of the plaster mould with wax, with the interior space filled with the original model (or rough clay), using pins to keep the inside and outside forms in position. The form is then heated so that the wax melts and drains out through hollow tubes called runners, leaving a narrow gap between the mould and the interior form. Into this gap, molten metal is poured until the space is filled. For a large sculpture, this might be done in sections, which are joined together after casting. Once the mould is broken away, the sculptor cuts off the runners (and also the risers which allowed hot gases to escape), tidies up any blemishes, and adds any engraved details required. Bronze can be finished to create a highly polished golden surface, but over time it acquires a rich patina, much darker or greenish in colour. Modern sculptors often create this effect right away by the application of acids. Click here to see a diagram which illustrates the lost-wax process.

It is possible for the sculptor to preserve the mould, or the model from which it was taken, so that the process can be repeated. It is therefore common to have more than one cast of a bronze sculpture.