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Casting is a fun and easy activity that can provide multiples of one
object in a variety of different materials.
In order to cast an object (let's say, a rubber ducky) in a different
material, first you must make a MOLD.
Once the mold is prepared, you can cast the original object in a variety
of material.
In order
to make a mold you can use plaster, although plastics is a better (albeit
more expensive) material.
A mold made of plaster is a rigid mold and therefore great care must
be taken to account for all the undercuts in the piece. Making rigid
molds of pieces that contain a great number of undercuts requires to
segment the mold to a large amount of pieces.
Here are
the basic steps to make a mold and a cast of a simple object:
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2
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create
a clay wall around half of the object |
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it
should look something like this |
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Option
1: Create a retaining wall so the plaster does not spill all over the
table. NOTICE the "plug" in the bottom of the object
designed to create an opening at the bottom of the object (all the wax
has to get in from somewhere, right?) |
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Since
the ducky's entire bottom does not need to be cast, it does not need
a "plug". The entire bottom will be open so the mold can receive
the wax.
DON'T forget the "Registration Marks"
The retaining wall is complete and I am mixing the plaster (off camera). |
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The
"Splash" coat is a thin coat of plaster that is splashed
on the object. This way the plaster is forced onto every detail of the
object. It is applied with a finger flicking technique. |
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Once
the splash coat is completed, I pour more plaster until the whole
object is covered. |
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Wait
for the plaster to set. Once the plaster gets hot and begins to cool,
you can remove the clay (but NOT the object) |
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Remove
the clay and turn the object over. The plaster now is now visible
around the Ducky. Construct a retaining wall again. |
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Plaster
sticks to plaster! So before you pour plaster, make sure to apply
a liberal amount of a separating agent to the entire surface (for
plaster common liquid soap will do). |
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Do
the "Splash Coat" routine and pour the plaster again.
Wait until it sets. |
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Open
the mold carefully. If it does not open, try to pry it gently at the seam.
Using compressed air at the seam often works to brake the surface tension. |
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Soak
in Water
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image]
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This
step applies only if you are casting in Wax:
Remove the object and soak the mold in water for about 15-20 minutes (more
time for larger molds).
If you do not soak the mold the wax will get stuck
in the mold |
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Melt
the Wax in a double boiler, and pour it into the mold. |
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Let
the wax cool and open the mold. Repeat as many times as you like.
Notice that you can cast hollow objects
by swirling the mold around after you pour wax in it. This way you build
a wax wall on the surface of the mold as it cools. Pour excess wax out
of the mold once sufficient wax wall has been built. |
