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The lost-wax bronze casting process - Bronze casting |
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Page 3 of 3
Bronze casting:
Preparing the wax copies:
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The lost wax process begins with the silicon mould being coated with a molten wax layer of about 4 - 5mm thick. It is removed from the mould when cool. |
Gating:
The sculpture is gated, with runners and risers made of wax which are joined by heat to the hollow wax sculpture.(These will act as air vents in the bronze pouring stage).
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Dipping:
The wax is hollow and will be filled with an investment mould held in place by pins. The outer sculpture will be covered in a ceramic shell, which consists of many layers of slurry and Shamot.
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Dipping wax in slurry
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Covering with Shamot
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Hanging to dry between layers
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Loosing the wax:
This is now put in the kiln, and heated until the wax pours out, leaving a hollow space.
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The kiln
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Pouring the bronze:
The hot, hollow mould is balanced in sand and the pouring cup placed upwards. Molten bronze, heated in a furnace is now poured in.
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The furnace
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Checking the temperature of the furnace
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Lifting the crucible from the furnace
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Pouring
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Pouring
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Chipping off the shell:
When cooled, the outer shell is chipped off, and the inside investment is drilled out.
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Cutting off the Runners and risers:
The runners and risers are cut off using an angle grinder and other tools, and the sculpture is sandblasted to remove any left over shell.
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Patina:
Lastly the sculpture has a patina put onto it’s surface. This can be many things but usually consists of chemicals which change the colour of the bronze to a reddish-brown, black or green. The sculpture is sealed with wax polish.
Research:
For me it is essential that I find appropriate and good reference material for any new sculpture I undertake. This can be through photography, observation, making drawings and watching videos of the chosen subject. This is so I can absorb the ‘feeling' and essence of the nature of my subject before starting. I gather and explore.
The maquette:
A maquette is essentially a small study for a larger sculpture. When I have an opportunity to create a large sculpture I use the production of a maquette to learn more about my subject and to establish the pose or structure that the final work will take. This is then shown to the client who has commissioned the large work so they have a good idea of what the final work will look like. At this stage changes are easy to make as the armature (skeletal structure) from such a small sculpture (up to 40cm height) is flexible and therefore easily altered. From this study I will 'scale-up' for the larger work, making the creation of the large armature easier with an accurate base for measurements.
I usually work with a wax (microcrystalline wax, paraffin wax, dye) or plasticine which I make from fine clay powder (ball clay), mixed into melted microcrystalline wax and some petroleum jelly. This is applied to a simple wire armature, and built up and modelled until I am satisfied. I can then use it as a reference for scaling up into a larger work or send it to the foundry.
I frequently have the maquette cast into bronze as it also make a wonderful sculpture.
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