Lost wax bronze casting

The "cire perdue" or lost wax-method has been used for thousands of years. The process has in essence never changed, though the materials and equipment used for moulding and casting have changed over time and from foundry to foundry. This page describes the process in a nutshell. The drawing below summarises it visually.

The lost wax method is a process that allows a sculpture, which can be made of any material, to be duplicated in bronze. It involves several stages in which the positive form is transferred to a negative one. This negative form is then used to create a positive once again.

With Tim Hannam at Bronzecraft foundry, 2022

Clay model of The Impostor with incorporated metal tractor seat

Step 3-4

The individual clay parts are moulded in rubber or silicone, which is covered on the outside in a more solid plaster for stability, like a protective egg shell. Once dried, the mould is cut in two halves and opened and the clay model removed. The moulds are now empty and hold the negative space of the clay form.

The closed rubber mould of The Gift

Step 9-11

empty mould is closed again and liquid wax is poured into the mould's negative space. Once cooled, the wax parts are liberated from the mould and reassembled into the shape of the original clay sculpture. Now wax runners and risers are attached to the wax form and the sculpture is now moulded in its entirety in a heat-resistant material. The wax is fired out of the mould and, once the mould is completely empty, bronze is cast into its negative space.

Multiple editions of The Gift

Step 1-2

I tend to work in clay and sometimes incorporate found objects, like a tractor seat in the case of The Impostor. When a form is complex, i.e. has lots of protruding parts, it would be impossible to release it from a two-part mould. In these cases the clay model is taken apart into parts which can be moulded individually.

The opened rubber mould of The Gift

Step 5-8

The empty mould is closed again and liquid wax is poured into the mould's negative space. Once cooled, the wax parts are liberated from the mould and reassembled into the shape of the original clay sculpture, i.e. a new positive has been created in wax. Now wax runners and risers are attached to the wax form and the sculpture is moulded in its entirety in a heat-resistant material.

The wax model of The Watcher I cast into the rubber mould

Once the bronze is cooled, the mould is removed and destroyed in the process. The wax runners and risers are now, like the sculpture, transformed into bronze. They are cut off and the bronze is cleaned up. With chemicals and heat the sculpture is finally patinated into the desired colour. When multiple editions are cast the whole process is repeated from step 5 onwards, i.e. from the casting of wax into the rubber mould. At the end of an edition the rubber mould is destroyed so no more bronzes can be created.