Sand Casting
One of the earliest methods of casting bronze, sand casting was a laborious process, reaching its peak of effectiveness in the nineteenth century. It has been described as tedious but Eleanor Milne enjoyed exploring the possibilities of sand casting at Bond Brass, even working directly with the sand.
The artist fabricates a mould from a specific French sand with binding qualities that can be packed around a plaster positive while maintaining its shape. The mould is divided into a number of pieces so the plaster model can be removed. Once the sculpture is cast, each piece has to be joined to the others. Rough spots and seams are removed through a finishing process. Sometimes to colour the bronze, special acids are used in a process referred to as patination. Nowadays polystyrene positives are used. They do not have to be removed from the packed sand as they can be evaporated off by heat. As in the lost wax method of casting, channels have to be inserted into the mould for gases to escape.
Lost Wax Method (Cire perdue)
The lost wax method of casting is considered
more effective than sand casting. While
earlier methods had to use piece moulds, contemporary foundries use silicone,
gelatin or rubber moulds. Because the mould is flexible, the sculpture
can be cast in one piece, saving time and effort, as well as allowing
the artist the ability to reproduce multiple copies of the work in the
minutest detail. Melted wax is applied to the inside of the mould and
an interior core is created. The gelatin mould is then removed and all
that remains is the wax that will be "lost" once the sculpture is cast.
At
this point, the artist is able to make alterations to the sculpture
by directly manipulating the wax. The artist then covers the wax with
plaster, making sure to create gates and vents in the mould for the gases
to escape. The mould is then fired, the wax disappears and molten bronze pours into the spaces left by the wax. Once the sculpture has cooled,
the plaster is chipped off and the bronze is filed and polished. It may
also be coloured, or patinated.
Eleanor Milne had visited foundries during her European trips to have her work cast. She was most familiar with the lost wax method of casting until she met Bill Bond in Canada. He was hoping to get his foundry, Bond Brass, into the art casting business. Art foundries had been rare in Canada until the beginning of the twentieth century. Mid-Canadian Investment Casting was one of only a very few art foundries in Canada, and many artists had to send their large works to Europe or the U.S. to have them cast until 1915.
References:
Encyclopedia of Science and Technology. New York: McGraw-Hill, 1997.
Untracht, Oppi. Metal Techniques for Craftsmen. New York: Doubleday Publishing, 1968.
Sand casting process with pictures posted by workshop leader Ann La Caze.
Lost wax process explained briefly by American Bronze Casting, Inc.
Lost wax process step-by-step with pictures on the Bronze Works Foundry virtual tour.
Lost wax process described in detail on Fonderie Coubertin website. You'll need Javascript to visit this site.
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