T he original sculpture for casting in bronze can be made of numerous materials.
In my own work for bronze I have modelled the original in clay, (terra cotta or stoneware), which gives a fine and subtle impression, almost down to a fingerprint.
On completion of the clay original, a silicon rubber mould in a plaster or fibreglass case is made by a specialist mould maker.
This mould is then passed to a bronze foundry. A hollow wax cast is taken from the mould and the sculptor is invited to make any reparations or changes that might be necessary.
Following this, a refractory cement casing is gradually built up around the wax sculpture, internally and externally, with runners and risers.
After cooling, this refractory cement mould is hammered and drilled off and discarded to reveal the bronze sculpture – which looks as if it has gone through fire!
At this stage, with large pieces, some blemishes may need the expertise of a welder. It is then sand blasted and chased to remove any small blemishes.
The final chasing is often carried out by the sculptor. A finish for the bronze is created with various chemicals depending on the colour required. This is burned into the sculpture, followed by hot wax.
Solid bronze casting is a labour intensive process using an expensive, but beautiful and durable, material.
The original silicon mould taken from the clay sculpture is still intact and can be used for further casts in bronze for a Limited Edition or in casts in other less expensive materials.
For example, cold cast bronze, using powdered bronze with resin and fibreglass is, relatively, much cheaper, but still has a similar appearance.
Much less expensive casts can also be taken in Herculite 2, a very strong but not weather resistant, plaster.
Sometimes the original clay head survives the mould making process and can be hollowed out and kiln fired.