HAMISH MACKIE 2013

At a time when contemporary art is criticised for lacking craft, bronzecasting is a refreshing antidote. Each sculpture takes on average fourmonths to be sculpted, moulded and then cast into bronze. It is ahighly skilled, labour-intensive process. Hamish’s sculptures are castin England by the Lockbund Sculpture Foundry. He has a 20-yearhistory of working with this foundry building a crucial relationshipbetween sculptor and founder; together rising to various technicalchallenges, from casting intricate feather detail to a life-size cheetahsupported on one leg.Whatever the sculpture, the finish is always of museum quality.‘You sculpt what you want and we’ll work out how to cast it.’ SimonAllison - Lockbund Sculpture Foundry.“I love the fact that a finger print left in the clay original comesthrough into the bronze. I take full advantage of the technicalcapabilities of a good foundry.”Bronze’s tensile strength allows compositions with minimal supports,unthinkable in materials such as marble, wax and plaster fromwhich sculptures are initially created. This results in tactile bronzesculptures that will last many centuries.Bronzes are made by pouring molten bronze into a ceramicinvestment - known as the ‘Cire Perdue’ or ‘Lost wax’ Method. Thesame technique dates back 5000 years. The skill of transforming onematerial into another is to preserve all of the detail of the original.Positive original to negative mouldThe first stage of making a bronze is to sculpt the original. Hamishuses different materials such as clay, plasticine or wax, dependingon where and what he is sculpting. This is built up over a steel andaluminium anatomical skeleton known as an armature. A siliconrubber mould is made over the original. The soft silicon rubber formsan exact negative of the positive original held in the right shape bya rigid fiberglass outer case. Multi-section moulds fit together withmillimetre precision.Positive wax to negative ceramicinvestmentThe ‘sprued up’ wax is then coated inside and out with liquid ceramicand grit, built up in layers to form a strong heat-resistant investmentaround the wax. This is then baked upside down in an oven, allowingthe wax to be burnt out - hence the term ‘Cire Perdue’ or ‘lost wax’.Negative ceramic investment topositive bronzeThe negative space formerly occupied by the wax is now filled withmolten bronze poured in at 1200ºC into the pre-heated ceramicinvestment. Other metals such as silver can be cast using the samemethod but at different temperatures.When the bronze has cooled, the ceramic shell is painstakinglyhammered away and the sprues cut off. To remove the hard ceramicfrom the surface detail and deep undercuts, the bronze is placed inacid, which further breaks down the investment.ChasingIf the bronze has been cast in several pieces, it is now welded togetherand chased. This is a highly skilled process recreating any surfacedetail. “It’s easy for me to push my fingers into soft wet clay, not soeasy to reproduce in hard metal; the sign of a quality casting is notto notice the chasing.” If structurally necessary, sculptures are fittedinternally with stainless steel supports.PatinatingThe sculpture is now ready to be heated up and applied with a widerange of chemicals, which form the finished patina. Hamish is one offew sculptors who do their own patination, as he considers this to beas important as the colour of paint on a canvas.Negative mould to positive waxMolten wax is slushed into the mould, poured out and the remainingskin allowed to cool; this forms a hollow wax positive approximately4mm thick. The seam lines where the mould sections fitted togetherare then worked out and the sculpture cut up into castable sections.To this a series of wax pipes called runners and risers are fitted(known as sprues); these allow the molten bronze to flow in and thegases to come out. Each time an edition is cast another wax has tobe made.65