The Alchemy of Bronze Casting

BRONZE - the casting process

there is a great distinction between real bronze and so-called cold cast bronze, which is in fact resin with bronze powder added. The production of a real bronze is a very thrilling, complex and labour intensive process. most artists work quite closely with the foundry and although not an expert I will give a brief description of the process.

The original sculpture for casting can be made from anything so long as the material used is strong enough to withstand being coated with liquid latex. I use wax and differing sorts of clays and also driftwood.

MAKING THE MOULD.
The sculpture is painted with liquid latex which has an accelerator added to it so that it becomes semi solid. For simple forms, for example the Pale Horses like Zingaro or The Magic Horse, it is often a two-part mould, like two halves of a walnut shell. More complex forms might need several shells.

LIMITED EDITIONS.
Most artists limit the number of castings made from an individual mould; in my case typically a sculpture will be sold in editions of between 5 and 12. This is done because each time the mould is used there will be a little wear and tear so eventually a certain amount of fine detail will be lost. The moulds are destroyed after the specified limit has been reached. Each bronze will have the edition number shown on it next to the artist's signature so number one of twelve will appear as 1/12, number two as 2/12 and so on.

THE WAXES.
Liquid wax is painted onto the inside of the shell until it is several millimetres thick. The latex is then eeled off and the wax shells are stuck together with liquid wax. Then wax “straws” or solid tubes are stuck on at various places, these will act as breathers or air holes for gas to escape at a later stage. Next a wax “core” or funnel is added.

FILLING THE GAPS.
Most bronzes are hollow. This means that the middle of the waxes must be filled with ceramic granules a bit like grains of wheat or rice. Once this has been done the whole thing is encased in Plaster of Paris.

LOSING THE WAX
The first stage of firing is when the wax encased in plaster is put into the furnace to burn off leaving the cavity which will be later filled by bronze.

THE FIRING
Chunks of solid bronze are added to the crucible and the furnace fired up; as the temperature climbs the bronze becomes like molten lava and is ready to be poured into the wax funnel or core.
This is the most dangerous and exciting step. As the molten bronze is poured into the mould the gases escape from the air holes, the whole thing is then left to cool before the plaster casing is broken off.

BRANCHY MONSTERS.
The bronze emerges from the plaster almost unrecognisable as the original sculpture because it is now a dusty white, in two or more hollow pieces and appears to have branches sticking out all over the place. These “branches” are where the wax 'straws' or 'breather tubes' were.

SAND BLASTING.
After the branches are cut off the bronze pieces are ready to be sandblasted to remove the last bits of plaster which inevitably lodge in any crevice.

WELDING.
The now clean bronze pieces are welded together into the final form and go onto the chasing shop.

CHASING.

One of the most skilful steps, a wide variety of tools are used to work the surface of the welds so that they are given the same texture as the rest of the bronze and are therefore completely hidden.

PATINATION.

This is the final stage. In the hands of a skilled person an enormous range of colours are possible. The bronze is heated with blow torches and then various different acids are applied which start a chemical reaction with the component parts of the bronze, this causes widely different colours to emerge according to the temperature and the dilution of the acid. At the very end the whole bronzeis coated with fine wax to seal the surface.

ALCHEMY - a personal story of bronze casting

My first experience of working with a foundry came when I took a driftwood horse to be cast into bronze. It was definitely jumping in at the deep end. The complexity of the form meant that the original sculpture had to be sacrificed; it had to be cut into ten separate pieces in order to make the moulds.

There was no chance that the beautiful original driftwood piece could possibly be put back together.It was agonising, I just had to trust in the skills of the foundry and in my intuition that it was the
right time to take what could be an expensive step if things did not turn out as
I hoped.

When the resultant castings were ready to be welded together I returned to oversee the process. I had been warned that there would inevitably be some shrinkage and distortion in the wax but even so I was not prepared for just how difficult it would be to regain the precise line and tension of the original form.

The foundry was incredibly noisy; the hot blast of the furnace seemed to amplify the shrieks of the grinders and a myriad hammerings made concentration difficult. It took hours of work and I suffered many moments of blind panic attacks when I was convinced that I would fail entirely, however I gritted my teeth and thanks to the endless patience, help and enthusiasm of the workforce, my horse finally came alive and was ready for the next step, the chasing.

This most skilled process was amazing to watch. I found that each “chaser” took enormous pride in their work and had usually made their own tools. Before my eyes the scars of the welds simply disappeared until the texture matched the original surface perfectly so that even I could not tell where they had been.

By this time the sculpture had been touched by many different hands and somehow seemed to have been invested with extra qualities too subtle to name, beyond the enduring strength of bronze and the original form.

Choosing what colours to use can make or break a bronze, but for me deciding on the colours was much less stressful than the welding, more like painting and when the piece was finally waxed and stood finished before me the whole nerve wracking experience was made worthwhile.

I had come to love the sounds and smells of the foundry and the time I spent there had set all manner of new ideas in motion.I began to use simplified forms and new materials; clay and plaster mixed with driftwood and I began to experiment with various finishes.The different drying times produced cracks and texture that spoke of antiquity. Suddenly I was in a world of myth and legend where anything is possible. Something odd seemed to happen to scale; although the pieces were small, they seemed massive and I was entranced as a whole new series of works emerged.

The unexpected sense of mass made me wonder what a life-size piece would be like and I got my answer in “Poseidon” a rampant horse that frightened my young Arabians so much that they would not come into the yard where he stood.

That was my experience of the alchemy that is bronze.