This slide shows the original sculpture (the positive), a bust of a WW1 Lighthorsemen, which has been hand carved from modelling clay by the artist, Carl Valerius. The positive model is then covered, front and back, with silicone rubber supported by a fibreglass or plaster casing.
This slide shows the cross section of the silicone and plaster casing. This is one side of the silicone mould, with the original sculpture removed leaving the negative of the front (pictured). The second side of the mould is of the back of the head. Several layers of liquid casting wax are then painted into both sides of the silicon rubber mould.
The wax inside both halves of the silicone mould is removed when set, creating a wax front and back of the head which is then joined together to make a positive, like the original sculpture but hollow. The slide to the left shows the wax replica from the above process. The result is a hollow positive shell of the original in green casting wax and is about 6mm thick.
The wax shell is then covered inside and out with ceramic material. Pins (chaplets) connect and support the inside and outside ceramic structure to ensure that all of the components are kept securely in place. The slide to the left shows the dark material being the wax and the light material being the ceramic shell. This structure is then fired to 1100 degrees to set the shell and burn out the casting wax - this leaves a void into which the bronze will be poured.
Air vents are constructed in the sides of the casing to ensure the consistent flow of the molten metal which is poured through a small hole in the top of the structure, filling the void. When the bronze has cooled, the casing is broken off to reveal the bronzed positive of the original sculpture.
The raw bronze is removed from the ceramic shell and cleaned with hat and strap added. The bust is then polished.
Patina (surface finish), is added by heating the bronze and chemically treating it to change the surface to the desired finish. This slide shows the final result. The patina is maintained by applying wax to the surface to protect it from the elements.