Bronze Fields Foundry

THE PROCESS OF CREATING A BRONZE SCULPTURE – LOST WAX PROCESS (CIRE PERDUE)

On commencement of a new sculpture Robert spends much time working on the composition, observing, drawing and sketching from life, using video footage and taxidermy which enables him to carefully study all the characteristics of his subject. This focused observation enhances the ability to capture the essence of the bird or animal in question and assists in its realistic depiction. A maquette, which is a small clay or wax model is then made to decide on the composition, the balance, the silhouette and the negative space of the sculpture. This will show what the full size sculpture will look like.

Robert is totally involved in the casting process from the first steps of the moulding to patination. It is highly unusual for an artist to be so hands on in such a complicated procedure.

BUILDING AN ARMATURE

The armature is the internal framework to support a large sculpture, which can be steel, polyurethane , wood and other mediums.

ORIGINAL SCULPTURE

This can be made in any medium but Robert prefers to use a mixture of microcrystalline waxes to achieve plasticity and strength to obtain the exact texture and detail required.

THE MOULD

The rubber mould is the method from which multiple editions are sourced. The edition number of the sculpture is determined by the sculptor. The completed sculpture is coated in a layer of silicone rubber. Some moulds, like the sculpture of the crested francolin took 22 sections to complete. Once the rubber has hardened it is encased in a fiberglass jacket. When the mould is completed, a wax copy is cast inside it, thus a hollow wax copy of the original sculpture is held in the rubber. This is achieved by melting wax to the right temperature to pour into the mould; the thickness of the bronze skin is determined by the thickness of the hollow wax shell. The wax picks up the finest detail from the silicone mould. Each wax is then individually fettled; the casting lines from the joins of the mould are removed.

The bronze is sprued in preparation for encasement in a ceramic mould. This gating system is made up of wax pipes, runners and a feeder cup attached to the mould, allowing metal and air to escape during the pouring of the bronze.

CERAMIC MOULD

This is built up in layers by repeatedly dipping it into liquid ceramic slurry and then into different grades of ceramic sand. About ten layers are built up using liquid ceramic and ceramic sands. It is then left to air dry. The ceramic mould is then turned upside down in a kiln and the wax is melted out leaving a cavity into which the molten bronze will be poured. At this stage the ceramic is fired to 600 degrees Centigrade.

THE BRONZE POURING

The bronze ingots are melted in a furnace to a temperature of 1200 degrees Centigrade, simultaneously the hollow ceramic mould placed the right way up and fired to 900 degrees Centigrade in a kiln. The glowing hot mould is then ready to receive the molten bronze which is poured into the ceramic moulds.

FETTLING

Once the bronze has cooled and hardened the ceramic mould is broken away to reveal the bronze casting. A hammer and chisel is used to shatter the ceramic shell, any remaining ceramic is sand blasted off until the bronze is completely clean. The different sections of the bronze sculpture are now welded together and then fettled using sharp chisels, grinders and files.

PATINATION

Liquid chemicals are now applied to the surface to accelerate the different oxides to achieve the desired patination of the sculpture which is then wax polished to seal the patination.