The lost wax process
The lost wax casting process is used for sculptures that are difficult in terms of form or where particularly high demands are made on surface accuracy and sharpness. If, for example, an artist has delivered a plaster model (original) of his sculpture to the art foundry he trusts, the casting proceeds as follows:
- First, the plaster model is embedded about halfway in a blind mould. This simultaneously defines the separation area for the mould halves. On this basis, the temporary plaster support shell is built up, into which the silicone is poured or applied. After cooling, the mould can be taken apart and the model removed. The negative silicone mould shows all the subtleties of the surface of the original.
- A layer of wax several millimetres thick is now applied to this negative form. It corresponds to the later wall thickness of the casting. A core (e.g. plaster and fireclay mixture) is poured into the wax sculpture. After it has solidified, the outer mould can be removed. The elastic gelatine or silicone mould releases the model that has been transformed into wax (wax preparation). At this stage, it can be reworked and corrected.
- Before the entire wax preparation is cast into a ceramic mass, the necessary pouring and venting channels for the inflowing metal are made.
- The solidified ceramic block is now placed in a kiln where the wax is melted out at high temperatures, thus creating a negative cavity in conjunction with the core.
- Then the casting takes place in the fired, highly heated mould. Once the metal has solidified and cooled down far enough, the ceramic mould is smashed to obtain the raw casting.
Now the work of the chaser begins
Carefully, he first cuts off the sprues. With his arsenal of special tools, he then carries out the reworking. Sculptures cast in several parts are welded together in an inert gas atmosphere. The welds are then reworked so that they are practically invisible. At the end of the finishing process, the casting must correspond as closely as possible to the original model, which the chaser constantly consults for comparison.
The final treatment
In bronze casting, this is done by the patinator. With his brushed-on, sprayed-on or burnt-in solutions, he achieves the desired patina through chemical effects on the surface. After a conservation treatment (beeswax, hard wax, etc.), the finished exhibit is now available to the client.