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.
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.
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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.
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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.
