Genesis of bronze sculpture Attraction
At first, an original sized model was built directly in plaster on top of a metal scaffolding. In the bronze foundry, the model was cut apart and a negative piece mould in plaster was made. The piece mould is held together by clamps.
Now wax is poured into the negative mould, about 4mm thick, in order to create a wax positive model. It is filled with a chamotte mass to evitate deformations. Now the waxmodel is furnished with channels which unite at a higher position. This will be the sprue for the bronze. Channels for the air to escape have to be put on, too.
Now the whole piece will be enclosed by a wooden shuttering and surrounded by chamotte mass.
The wax positive with the channels is supported from all sides and ready for the oven. It goes into the oven for 2-3 days, is heated up and cooled down slowly, so that the wax will evaporate completely.
Depending on the size and shape of the sculpture this can vary and the temperature has to be controlled – the wax mustn’t burn, or leave residues. The complete waxmodel and all channels are now a cavity in the now hardened chamotte mould.
This is the magic moment of bronze casting. The bronze has been heated up to 1000 degrees celsius mor or less – here again, the sensibility and experience of the caster is essential. The bronze melt mustn’t get too hot, it would produce soot and bubbles. It still has to be hot and liquid enough to fill out every corner of the cavity.
The casting bucket filled with bronze melt is lifted up by the casters with high concentration, they pour the bronze melt into the cavities of the chamotte mould until the cavities are filled up completely. The remaining bronze melt is poured into bar moulds immediately in order to cool down and harden till the next casting ist done.
After a while, the chamotte can be carefully knocked off and the hardened raw cast is visible.
As soon as the bronze has cooled down completely, it will be cleaned from the inside and outside. The ciseleur then cuts off all the channels, reunites the single parts of the sculpture by welding, grinds down surplus edges, and welds little holes.
The last step is patination. The bronze is heated and through a chemical reaction, a patina is burnt into the surface, f. ex. with sulfur.
