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This step is the very important to the finished piece and
requires a working knowledge of the casting process. Timing and
temperature are extremely important. If the casting process is
performed improperly the entire piece may be lost.
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The
Heating of the Mold
The mold is
placed within a small igloo-type house of bricks. A fire is
lighted around it. The fire is very hot to burn out all the wax
from the interior of the mold. During the firing you can see
the wax actually burning out of the piece by a little fire at
the pouring spout. |
Melting the excess wax from the earthen mold |
Varun & Varadaraj inspecting the mold being fired |
The
following is how long it takes to melt the wax out of a mold;
1 hour for a 12 inch wax mold
1 hour for a 24 inch wax mold
2.5 hours for a 36 inch wax mold
4 hours for a 48 inch wax mold
8 hours for a 60 inch wax mold
10 hours for a 72 inch wax mold
The Heating of the
Metal The
metal must be heated in conjunction with the firing of the mold.
Bronze is a combination of copper, zinc, tin and small
amounts of silver and gold resulting in what is called Panchaloha
bronze. The Bronze Creative has developed a heating method using
propane gas for heating the metal. Using propane allows the artist to
control the exact heat of the fire. The old method was to use large
amounts of wood for extended periods of time to heat the metal. This
was bad for the surrounding trees as well as an inefficient and wasteful
way to heat the metal. However, the new method of using propane also
emits carbon into the atmosphere so neither is a perfect solution.
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The metal is
heated in special clay containers called crucibles from
Andra Pradesh that are four different sizes depending on the
size of the statue within the mold. |
Placing the metal into the crucible |
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Weighing the metal |
The weight of
metal that is melted is proportionate to the weight of wax
model. For every 1 kg of wax the artist must melt 10 kg of
bronze. Thus it is important to weigh the wax mold in the first
step of the process before the earth mold is made.
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The metal is heated until the metal is completely
liquid. Long iron rods are used to mix the metal and to check for
liquidity.
The
following is how long it takes the metal to melt while being heated;
45 kg of metal takes 2 hours to melt
60 kg of metal takes 3 hours to melt
120 kg of metal takes 4 hours to melt
750 kg of metal takes 5 hours to melt
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Firing
process is long. During the process a lot of dirt and unwanted
material enters the crucible. A large spoon or ladle attached
to a long iron pole is used to scoop up the excess waste on top
of the liquid metal and is then discarded into an iron bowl.
Because the liquid metal is denser than the dirt the dirt is on
the top of the liquid metal and is easily scooped away. This
causes a safety hazard as some metal usually is dropped on the
ground. For this reason castings are always performed at night
when the molten metal is easily spotted on the ground and can be
avoided. |
Using a spoon or ladle to remove excess dirt |
The excess dirt is placed in a pan so no one steps on it |
Once the metal is melted, the excess dirt is removed and
all the wax is burned out of the earthen mold the piece is ready to be
cast.
It is very important that the metal turns to liquid and
all the wax is melted from the mold at approximately the same time.
This is the correct time for casting to ensure a positive result.
Depending on the size of the crucible being used for the
casting 1, 2 or 2 people and pulley system are used for the pouring of
the metal. The crucible is picked up out of the fire and brought over
the mold placed in the ground. Moving the liquid metal is extremely
dangerous. Happily the Bronze Creative has a perfect safety record with
only minor burns experienced during castings.
Pouring the Metal
A burlap bag is added to the top of the crucible and is ignited by the
heat. The burning bag performs 2 functions for the casting process. It
acts as insulation maintaining the high heat of the top layer of the
metal. During pouring it also acts as a strainer, catching any extra
waste materials that were not removed by the spoon.
The crucible is then tilted and the liquid metal freely
pours into the pouring mouth of the mold. If all the wax was not
completely melted out of the mold the mold violently regurgitates the
liquid metal out of the pouring mouth making it absolutely essential
that all the wax is melted out of the mold.
The casting process is complete and the mold is allowed
to cool off.
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