Tab: Hamish Mackie - Bronze Casting (DO NOT DELETE)
Hamish has always been fascinated by the fact that it is technically possible to reproduce the detail of a fingerprint in bronze. "It's easy for me to push my fingers into wet clay, not so easy to reproduce it in metal."
Bronze castings are made by pouring molten bronze into a ceramic investment - known as the Cire Perdue or 'Lost wax' Method. This remains essentially the same technique as it was in 2,000 BC. The skill of transforming one material into another is to lose none of the original detail.
Hamish's sculptures are cast in England at the Lockbund Sculpture Foundry, Oxfordshire and Atelier Fine Art, Hampshire. "Who's enthusiasm and skill is elemental to what I do." The stainless steel Tuna was cast by the alloy specialist Lost Was Developments.
The first stage of making a bronze is to sculpt the original out of clay, plaster or wax. Hamish uses different materials depending on where and what he is sculpting. This is built up over a steel and aluminium anatomical skeleton known as an armature.
Over the original a silicon rubber mould is made to form a negative of the original.
Into the mould molten wax is slushed in and then poured out and allowed to cool, to form a hollow wax positive.
The seam line where the mould fitted together is then worked out and the sculpture cut up into castable sections.
To this a series of wax runners and risers is fitted, and these allow the molten bronze to flow in and the gases to come out. Once the wax is 'sprued up' it is coated inside and out with liquid ceramic and grit built up in layers to form a strong heat-resistant investment around the wax.
This is then baked upside down in an oven allowing the wax to melt out - hence the term 'Cirdu perdue or lost wax'.
This forms a negative space of the original into which molten bronze can be poured at 1200°c. Other metals such as gold, silver and stainless steel can be cast using the same method.
When the bronze has cooled, the ceramic shell is chipped away and the sprues cut off. To remove the ceramic from the surface detail the bronze is placed in acid, which breaks down the investment.
If the bronze has been cast in several pieces, it is now welded together and chased. This is a highly skilled process recreating any surface detail.
The sculpture is now ready to be heated up and applied with various chemicals, which form the finished patina. Hamish is one of few sculptors who do their own patination, considering this in his mind as important as the colour of paint on a canvas.