Tenfold • The Making of a Bronze
Bronze has been used to cast sculpture since ancient times. Today, modern techniques and materials are used but the process remains the same, the one man has been using for 3000 years. If a foundryman from ancient Greece or Rome could visit us today many things would be familiar, so we really are part of a long and magical tradition.
The casting process is called the lost-wax process because it requires creating an exact replica of the original sculpture in wax. This pattern in then encased in a mould and heated in a kiln to burn away the wax leaving a cavity to fill with molten metal. This mould is then broken away to reveal the casting.
Lost-wax is perfect for casting sculpture because any shape can be cast and fantastic ‘finger print’ surface detail from the original sculpture is reproduced.
Enlargement
Creating large sculptures requires teamwork and the foundry will often help sculptors to enlarge their work. This highly technical process is carried out using a pantograph or ‘pointing machine’. The form of a small sculpture or ‘maquette’ are measured and the information transferred on to a large metal frame or ‘armature’ which is covered in clay. This creates a perfectly scaled up version of the original maquette which the sculptor can then refine completely.
Mould
The first stage of the casting process is to make a mould in silicon rubber. The flexible rubber creates a negative version of the sculpture – a container into which we pour molten wax. The mould can be used many times allow the artist to make more copies of the sculpture – usually a limited edition which is numbered and signed for authenticity.
Wax
The hollow wax is a replica of the original sculpture and all mould seams need to be skillfully worked. Art foundries have always formed close working relationships with sculptors. The artist will often come to the foundry to check it before casting. It’s a chance make any minor changes as the next time they see their sculpture it will be in bronze. Some sculptors prefer to sign the work at this stage.
Shell
Now another mould has to be made ¬this time in ceramic. On the wax we stick wax bars called ‘runners’ and ‘risers’ which will allow the molten bronze to fill the mould and air to come out and a ‘cup’ in which to pour it. The whole piece is then coated in a ceramic material in layers to form a thin ‘shell’. This is fired in a kiln at very high temperature to achieve two things; it melts all the wax out, and fires the ceramic to create a pot – strong enough to pour bronze into.
Pouring
The bronze is melted in the furnace to a temperature of 1120 degrees centigrade and then carefully poured into the shell. It’s an exciting time when in the noise and the heat of the foundry the sculpture is cast, the shell broken away and we get to see the results of our efforts.
Metal
Once cast, half the work is complete. Now different skills are needed to finish the bronze to recreate in metal all the forms and marks from the original sculpture. Large sections are welded together and the surface must be worked to lose all traces of the process. Sometimes the work requires polishing or the adding of textures. The metal worker needs to have a clear understanding of what the artist wants and the expertise to do it.
Patination
Finished bronzes come in an endless array of colours but the metal itself is the same. We achieve the colours by applying different chemicals to the heated surface, which react with the copper in the bronze. This can be controlled by a skilled craftsman who works closely with the sculptor to achieve the desired effect. A coat of wax is then applied to the surface to seal and bring out the richness of the colour.
