is the process of reproducing a 3D image using a mould to produce
a replica in another material e.g. bronze. The process for these sculptures
uses the lost wax and ceramic shell methods for bronze casting. This
involves the following five stages;
silicon rubber coating of the original. Rubber coating is constructed
in sections to enable the mould to be removed from the original, and
access to the inside surface and retrieval of the wax positive later
A strong fibre glass jacket is layered on top of the rubber to support
it. This mould holds a negative image in rubber of the original.
hollow wax positive of the original is cast from the mould by slushing
hot wax into it. The thickness of the wax corresponds to the eventual
thickness of the bronze eg.10mm. The wax positive is worked on to
make good any imperfections e.g. seamlines, air bubbles. A network
of wax rods (sprues) and a funnel- like cup are fitted onto the positive.
These become the channels for the molten metal to travel to the job
later in the process.
sprue system and wax positive are coated with a liquid whose ingredients
include sodium silicote. The liquid is combined with molicite granules
to form an extremely hard shell around the wax when it is dry. The
shell is built up using five or six layers like the above, and backed
up with fibre glass matting in the liquid, so that the resultant shell
is strong enough to take the heat shock it will receive later. The
inside cavity of the hollow wax positive is filled with a plaster-based
mixture which is called core. The wax is then melted out of the ceramic
shell using a high powered blow torch heated up in a kiln leaving
a negative space in the shell ready to receive the molten bronze.
bronze is melted to a high temperature in a crucible using a furnace.
bronze is then poured from the crucible into the shells, which have
been set into packed sand for extra strength. Leaving ten hours for
the bronze to cool, the shell is then ready to be chipped and washed
off the metal casting. The cast is a replica of the wax including
the sprues and funnel cup.
finishing and Patination
The sprues are cut off (fettled) and the metal surface worked on to
repair any casting imperfections (chasing). Large pieces that are
cast in sections are welded together, and the welds chased back to
blend in with the form. The finished bronze is coloured (patina) by
applying various metal oxides to the surface often using heat. The
bronze can then be waxed and polished to slow down the natural oxidising
process of the bronze or left natural