Making Bronze
Whilst the earliest use of cast metals by man is lost in the mists of the past, we do know that sometime between 3000 and 4000bc, bronze was created by mixing a tiny bit of tin into molten copper. The introduction of the tin made the resulting metal heavy and hard; the Bronze Age began.
Bronzes are either Lost wax cast or sand cast, Lost wax being used most often and especially for small pieces or where an edition is wanted and sand casting direct from an original sculpture for very large bronzes. Both processes were used from the time of the early Egyptian dynasties.
The process of ‘Lost wax’ bronze casting starts with the creation of an original piece of sculpture (I work in clay, a wax mixture or plastilene, which I build up on an ‘armature’ made of wire). From the finished sculpture, a mould is made using rubber, with an outer case of plaster for strength. Molten wax is then poured into this mold to create a replica of the original. The wax replica is then covered in a ceramic mixture, which is hardened creating a brittle case or ‘waste mould’. The waste mould is heated so that the wax melts out (Lost Wax) via runners and risers attached to the wax, leaving an empty shell with a reverse impression of the sculpture. Molten bronze is poured into the waste mould at temperatures exceeding 1000 degrees. When the bronze inside has cooled, the mould is cracked away, revealing the bronze sculpture.
The final processes are the Patination and Waxing. The Patina is created by applying certain chemicals that react with the bronze to create the unique colouration. The finishing coat of wax protects the bronze and gives it the subtle and lustrous sheen.