clay to bronze:
the art of lost wax
In the third millennium BC, somewhere between the Black Sea and the Persian Gulf, an artist crafted a vision in beeswax, covered it in clay and cooked it in a fire. In the flames the wax was lost, replaced by empty space. Tin and copper—alloys of bronze—were gathered and heated. Once melted, the metal was poured into the cavity of the fire-hardened clay. The metal cooled and the sculptor knocked the clay from the metal. The first bronze was cast.
Certain elements of the ‘lost wax’ process have been refined, yet today bronze casting remains essentially the same as it was in 2000 BC during the Akkadian period.
The following pictorial series illustrates an example of this process:
the gymnast
A steel armature is made to support the clay sculpture.
Working on the clay image
Silicon rubber is painted on in layers.
Plaster moulds are made over the rubber in removable sections. This often also involves sectioning the sculpture.
Once the plaster has set the sections are removed, the rubber is cut open, the clay is removed and the mould is put back together.
Hot wax is poured into the mould, sloshed around and poured out. This is repeated until a hollow wax about 1/2cm in thickness is achieved.
A gating system for entry of the bronze and exit of gases during the pour is added.
The hollow wax is then invested inside and out in either a plaster and sand mix, or a ceramic shell.
The wax is then burned out in a kiln and the bronze is poured into the space which is left.
The investment material is then broken off the bronze.
The bronze is cleaned by sand blasting and the gates are cut off.
The sections of bronze are welded together and the joints resurfaced to match the desired finish of the surface of the sculpture (chasing–see below).
The final colour is created by the application of a variety of chemicals to the surface following heating (patination).
This can be rubbed back for different effects and a layer of wax or lacquer is then applied.
The finished piece.