British figurative sculptor David Williams-Ellis explains the process of casting a bronze sculpture
One of the many questions that David Williams-Ellis is asked is ‘what is the process of casting a bronze?’
Here, David explains some of the art and science that lies behind the bronze sculptures for which he is particularly known.
I generally work in clay using the “lost wax” method. It is essential to ensure that the clay doesn’t dry out between working on the clay and making the mould.
A rubber mould is made by effectively covering the original clay model with a clay blanket (for a life size sculpture this is done in sections).
The clay blanket is then covered with plaster to achieve a sandwich of plaster/clay blanket/clay model/clay blanket/plaster.
Clay model of Nubian Girl with arms removed showing plaster casing on the bottom half and clay wall to separate the mould
The plaster casing is then opened and one side of the clay blanket is removed.
Silicon rubber is poured into the void, replacing the clay blanket. This is then repeated on the other side and once the rubber has set, the mould is opened and the original clay figure removed. You are then left with a fingerprint impression of the original clay in rubber.
Showing the back of Nubian Girl embedded in rubber mould prior to the back casing being replaced and rubber being poured in
Hot, liquid wax is then painted into the mould, which hardens when cooled. The rubber and plaster casing are peeled off to leave a hollow wax fingerprint reproduction. The wax is usually around 3-7mm thick.
The seams of the wax are then tidied up and you are left with a finished wax version of your original clay, with what will effectively be the final bronze.
Any detail – faults – in the wax will show in the finished bronze and so, at this stage, you have to be very careful in repairing any imperfections. You also have to check the integrity of the wax. I then sign and date the wax.
To transform the wax into a bronze, “runners” – pencil thin sticks of wax – are placed at various junctures onto the figure (these are eventually used to pour the bronze into the mould). The wax is then covered and filled with a ceramic shell which, when baked, becomes brittle pottery. In the process of “baking”, the wax is melted out of the shell leaving a ceramic shell mould.
Molten bronze is then poured into the shell. The end result is a bronze figure covered with rods of bronze, where the wax runners were attached to the original, which need to be removed. The ceramic shell is then chipped off and the shell taken from the inside, leaving a very dirty looking bronze with holes and marks on it.
The “chaser” (the metal worker) then comes in to weld up any holes in the bronze and any unwanted protrusions. This leaves an ugly, shiny, raw bronze – rather like gold powder paint.
In order to get the patination (colour), you need to heat the bronze with a blow-torch. This is then brushed with chemicals so that oxidization takes place and gives the sculpture its finished colour. For example, Cupric Nitrate is used to achieve green, Ammonium Chloride – liver brown, and Ferric Nitrate – rusty brown.
Hot wax can then be brushed on to seal and protect the patination which, when buffed, gives you a shine.
The finished bronze!
For further information on David Williams-Ellis, please visit www.dwe.com
Images courtesy of Sophie Poulton