Bronze Casting: The Lost Wax or Cire-Perdue Process
The lost wax or cire-perdue process is the traditional method
of bronze casting . It has been around for at least 5000 years and
was used by the early Egyptians, Greeks, Africans and masters of the
Italian Renaissance. A complicated and difficult process, it includes
the following steps:
A sculpture is created over an armature out of clay or plaster.
- A flexible rubber mold with a rigid jacket is made of the sculpture.
- The clay/plaster is removed from this mold and it is
cleaned out thoroughly.
- The mold is tied together and wax is poured inside.
- The mold is removed and the seams and any casting
imperfections are cleaned up by the artist.
- Wax sprues and vents are attached to the sculpture so
that the bronze can eventually be poured into the piece and gases can escape.
- The piece is invested by making a mold of plaster mixed
with grog around the wax.
- The investment mold is placed in a burn-out oven to melt
the wax out and dry the mold.
- Bronze, which is an alloy consisting mostly of copper
with small amounts of zinc, tin and lead, is melted in a crucible to
a temperature of approximately 2000 degrees and poured into the
warmed investment mold.
- After cooling, the investment mold is tapped off and the
sprues and vents, which are now bronze, are removed and chased.
- The piece is sandblasted to clean the surface of the
bronze from scaling and acids and oils.
- A patina is applied to the surface. This is a chemical
process that is etched into the surface of the bronze.
- The finished bronze is now lightly waxed to preserve its patina.
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