'By the Dawns Early Light'
Bald Eagle Bronze - 11.5
Casting the bronze
Bald Eagle Sculpture using the 'lost wax' method
Investment casting is a modern method of making bronze castings using the
ancient art of the lost wax process to a high degree of accuracy
and also with a smooth surface finish. Outlined here are just some
of the various stages required to produce a typical bronze casting from the
original master copy to in this example, the completed Bald Eagle
The master copy of the Bald eagle was originally carved from lime wood, the surface
of the wood sculpture was then bleached, stained and sealed with a wood
sealant to help prevent the rubber mould sticking to the Bald eagle
Using the original eagle as the master copy,
a flexible 'negative' rubber mould with a hard plaster 'jacket' was produced.
The making of this negative can begin once the most suitable joint-lines on
the original sculpture has been decided upon, which will enable the
sculpture to be removed from the mould, without either damaging the
original woodcarving or the rubber part of the mould itself.
A thin coat of wax is applied to the original
wood sculpture which will help prevent the rubber sticking to the
woodcarving, then a layer of soft clay is placed over the whole
sculpture, which in turn is followed by a layer of moulding plaster to
make a 'mother-mould'. Each half of this mother mould is then removed
and the clay extracted, the liquid rubber is then pored into the space
left by the clay and allowed to cure. Once the master copy is totally
enveloped with the moulding rubber, the plaster 'jacket' can be removed
and the flexible rubber stripped from the original Eagle sculpture.
The flexible rubber is then placed back into the
plaster jacket and melted wax can then be either painted or swilled against
the inner surface of the rubber to the desired thickness required for the
finished metal casting. When the wax has cooled the hollow wax replica of
the original sculpture can be removed from the rubber mould and the 'runner
system' or 'tree' to channel the molten bronze is applied to the wax.
various different patterns drying out
When these wax eagles are assembled
upon the wax runner,
the complete assembly is then dipped or invested into a wet ceramic based
slurry and coated with a fine dry refractory similar to these various patterns
shown above. Once dry these coating operations are repeated several times and
by progressively using coarser grades of refractory until the mould
eventually reaches a sufficient thickness to withstand the force of the molten
metal during the casting operation.
pouring the molten bronze
into the hot ceramic shells
when cooled the bronzes are removed from the shell
Once all these various coats of ceramic
have been applied and the 'tree' has been dried the ceramic shell
is then placed in a steam oven and the wax is melted out - hence the
name the 'lost wax process'. The shell is then fired at 1000.degrees centigrade
to burn off any residual wax and to strengthen the ceramic mould. Once the
bronze is melted in a high-frequency induction furnace it is poured
into the hot shell, enabling the bronze to flow into all the detailed sections. After solidifying
and cooling the ceramic shell is broken away from the bronze cast and
the castings are cut away from the tree.
the polished bronze
prior to colouring
Hours of careful fettling is then required to clean up and finish the
eagle sculpture, the bronzes are then polished before the
various finishes are ready to be applied.
patina - ( A )
A traditional bronze patina colour to the bronzes is usually achieved
by painting on a chemical solution to the whole bronze casting
whilst the bronze is cold. The weaker the solution the lighter the colour,
when the correct colour is finally achieved to the sculpture, the
bronze is heated up with a gas torch and melted bees wax is painted on to
the bronze to seal in the colour and the sculpture is then allowed to
cool slightly before it is finally polished with a soft brush.
Coloured Bald Eagle
- ( B )
In the case of the Bald Eagle to try and achieve a similar 'bald eagle'
look without painting the sculpture, i.e. a lighter colour head, tail,
feet and beak, this can be achieved by carefully applying a with
a brush a stronger chemical solution to the body of the Bald Eagle to
achieve the almost black colour required of the eagles body feathers. By
then applying a much weaker solution to the head, tail, feet and beak, the
bronze is again then heated up and melted wax applied to seal in
the colour of the bronze.
Painted Bald Eagle -
( C )
To achieve a
similar but possibly a more naturalistic appearance to the Bald Eagle this
can be achieved by painting the bronze using acrylic paints and
then wax polished. As before the almost black colour of the eagles body
feathers is achieved by painting on a stronger solution of the
chemical and sealing the bronze with wax. Once the sculpture has
again cooled down from being heated with the gas torch, the bald eagles
head, tail, feet and beak can then be prepared for painting. The painted
area on the bronze has to first be sealed with a metal primer before
the white and yellow acrylic paint is applied, the whole sculpture is then
given a final polish with wax..
Further examples of Ian's smaller
wax sculptures assembled upon the wax 'tree', prior to the wax runners and
risers being attached.