PLASTER WASTE MOULDING

The waste mould is a relatively simple method of creating a hard plaster copy from a soft clay model. The plaster cast copy is easily transported and can be handled in the foundry as it progresses through the casting cycle with little fear of sustaining serious damage. The resulting plaster cast can also be re-worked and refined by the sculptor in a to a degree not always possible in soft clay. The sculptor can even tint the plaster cast with a pigment to help determine the most appropriate patina colour for the finished work.

To make a waste mould, the sculptor or their assistant presses a SHIM border into the clay model, thus dividing the model in two (or more in some cases). First one side of the shimmed clay, then the other, has a plaster case built up to create a mould of two (or more) pieces. The plaster casing is pulled away from the clay, the clay removed and the remaining 'negative image' plaster mould pieces are washed clean. The mould can then be reunited, secured and filled (with plaster, ciment fondue or other robust material). The sculptor then carefully chips away the plaster case to reveal the underlying copy of the clay original.

TIP: Care must be taken to ensure air bubbles are absent from the layers of plaster that contact the clay's surface, careful mixing and gentle blowing will often disperse trapped air pockets. Also, add a pigment to the first layer (in contact with the clay), this acts a surface proximity alert when chipping away the waste mould.

Some of the finest examples of waste moulding can be seen in the plaster works of the French sculptor August Rodin (1840-1917). Many of Rodin’s plaster sculptures were specifically created for art foundry use (as master patterns). What makes Rodin’s work particularly interesting is his habit of leaving shim division lines across the surface his cast plasters as an intrinsic feature of the work. From these seam lines, the viewer can gain an insight into the working methods used for the construction of the waste mould. Many plaster copies of Rodin’s sculptures are still in existence, unfortunately not all of these are believed to be ‘authentic’ (copies produced to the sculptor’s direction and under studio supervision). The best places to view examples of Rodin’s plaster work are the Museé Rodin and nearby Museé D’Orsay in Paris.

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