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(A brief description of
the lost wax casting process)
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| The lost wax process is a
traditional method of casting bronze sculpture
which goes back in time to something like 5000
years. It is still used today in the casting of
bronze sculpture because of the ability to
achieve very fine detail and deep undercuts
although more modern equipment and methods are
used nowadays. |
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1 Mould Once
the clay original is finished you are then ready
to take a negative mould from it using a flexible
rubber type compound this is either painted onto
the sculptured surface or poured between the clay
sculpture and a plaster jacket. The mould should
really be made in at least two parts or more
depending on the size or complication of the
sculpture. You now have a rubber negative mould
supported by a plaster jacket this mould is going
to make a hollow wax positive of the original
sculpture. |
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Two
part mould with clay original
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2 Waxing up When
the rubber/plaster negative mould is finished you
are then ready to start applying melted wax to
the surface of the rubber mould using a paint
brush. After several coats of wax the mould is
assembled and cool wax is then poured inside to
completely fill the mould. It is left a few
seconds to increase the section thickness and
then the rest is poured back into the melting
pot, you now have a hollow wax positive. When the
wax has solidified the cavity is then completely
filled with plaster and grog, this is called the"Core"
and is done to eventually achieve a hollow bronze
casting approximately 1/4" inch section
thickness. |
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Waxing up using
brush
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3 Retouching wax The
sculpture now in wax with core inside is ready
for the artist to tidy up all the seam lines from
the waxing process and to sculpt the fine detail
before being finally signed and dated. Nails are
now hammered halfway in through the wax into the
core all over the sculpture, these nails keep the
core central when the wax is melted out in the
kiln. |
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After retouching
wax nails are inserted
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4 Runners &
risers Wax runners are
welded to the bottom of a pouring cup using a hot
knife and go to various parts of the sculpture,
when melted out these wax runners will leave a
cavity for the molten bronze to flow to the
sculpture. Risers are then attached to the top of
the pouring cup these will act as vents to
release hot gases and air from the cavity of the
mould when the bronze is poured. The wax
sculpture with runners and risers is now ready
for plaster and grog (investment) to be applied
to make the outside mould. |
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Runners &
risers fixed to wax head
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5 Investment mould
An initial layer is applied to the wax
sculpture until the thikness is about 1/2"-3/4"
by dipping or painting. A steel or plastic sheet
is then wrapped around the sculpture and sealed
at the bottom, investment material is then poured
in until it reaches the top of the wax pouring
cup. The mould is now ready for burning out in
the kiln prior to casting. |
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Wax sculpture
encased in investment
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6
Burning out & casting The mould is
placed in the kiln and slowly taken up to
temperature over 48 hours depending on the size
of mould, this will drive all moisture out of the
investment and melt out the wax leaving a cavity
for the molten bronze ( hence the lost wax
process).
The mould is taken out of the kiln and put into a
pit or steel ring packed around with sand to stop
it from splitting when casting. Bronze is then
melted to approximately 1200 degrees centigrade
depending on the grade and then steadily poured
into the mould.
When everything has cooled down the mould is
split open and the investment is carefully
chipped away to reveal the bronze sculpture with
it's runner and riser system. The sculpture is
now ready to have it's runners and risers taken
off and the surface of the sculpture fettled/chased
a process of working the sculptured surface to
the desired finish.
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After burning out
the mould is poured
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The above process is very time
consuming taking many weeks by skilled craftsmen.
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Christine
Beardwood
Ridgequest Foundry, Croft Road, Croft, Skegness,
Lincolnshire, PE24 4PA, England.
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Artist
copyright Christine Beardwood
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