Lost-wax casting

Patricia Thomas and William Wright

Lost-wax casting is method of making metal objects, whether ornaments, pieces of machinery, tools, jewellery or religious items. The process converts a wax model into finished metal product of the same size and shape. The wax model is melted away or “lost” during this casting process, producing metal parts to precise dimensions. Lost-wax casting enables metal items to be made profitably, on small-scale and using local resources. It is very easy and satisfactory technique which has stood the test of time used by the ancient Egyptians and still widely practised today. Tourist markets in many countries sell metal ornaments made by this time-honoured technique. Aluminium, brass, bronze, copper, gold, iron, platinum, silver, steel, tin or zinc may all be used in pure or alloyed state.

Using lost-wax casting to make a model

Items required

Beeswax:

bellows;

burlap (sacking);

clay;

rice husks or straw to reinforce the clay; c

ow dung; charcoal;

a metal file;

a metal grid;

scraps of metal;

a soft cloth;

tongs.

1. The artist forms a solid mass of clay and allows it to dry in the sun until it is very hard. The shape of the clay needs to be roughly the shape the item to be created. The item being made here is model fish. Once the clay has hardened thin layer of beeswax is fitted around it.

2. The artist moulds the features from softened beeswax working on an oiled board. Fish scales are represented by intricate spirals made from long, thin rolls of beeswax. The artist keeps the beeswax soft while working by occasionally warming it near fire (but not too near!). The parts are applied to the wax model of the fish’s body, and the model hardens.

3. Some more clay is now prepared and reinforced with cut burlap (sacking) pieces, rice husks or straw for added strength. A rod-shaped piece of beeswax about 2 cm in diameter is attached to the fish. This will serve as spout to drain the beeswax out and to then allow the hot metal to enter. The reinforced clay is packed tightly around the fish and the rod. Using the a shallow bowl with 2 cm hole is moulded at the end of the beeswax rod.

4. The clay-covered beeswax form is now placed in the sun for two days to harden. After this it is then put on grid above charcoal fire in pit that is two feet deep. The fire is insulated with large scraps of metal. Its intense heat is enhanced by the constant pumping of bellows made from welded pipes and animal skin.

5. The worker waits until it becomes clear that the wax is melting. The figure is then lifted from the fire with long metal tongs and turned upside down. About half the beeswax can be drained and saved for future use.

6. An odd assortment of metal pieces collected by the family serves as the “bronze”. All the pieces are broken into small, manageable chunks. Workers use trial and error to determine the weight of metal required to produce particular object. It is always better to have too much metal than too little.

7. The metal chunks are placed in deep bow! made of reinforced clay. This bow! containing the metal is now attached to the clay mould, and it is allowed to harden in the sun for day. The mould is then placed in fire with the bowl downward. After about seven hours, the sound of metal can be heard sloshing inside: the metal has liquefied.

8. The form is lifted from the fire and turned upside down. The liquefied metal flows down through the spout into the mould.

9. After cooling, the clay mould is broken away. The bronze fish emerges and is left to cool completely. The metal spout is removed and rough surfaces are filed smooth. The filing gives the surface a shiny finish. Some workers prefer an antique finish painting the surface with burned millet stalks that are ground into powder and mixed with water. After the sixth coat, the bronze is buffed with a soft cloth until shiny.

* Please see the original journal article to see images of the above steps.

Book: Lost-wax casting: practitioner's manual

by W Feinburg (1983) 74 Pages. Paperback.

This manual has been written for craftworker sand people with limited money, and is based on the author's experience of working in counties where the ideal materials and equipment are not always readily available. The manual is designed to encourage resourcefulness in building equipment, and to stimulate new interest in this valuable technique.

This manual is available from Bees for Development price £8.30. For details of how to order see Books to Buy (enclosed) or Bookshelf, page 14.