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HOW
TO "SHRINK" AN OBJECT
The
Castcraft Guides
show how to "enlarge" an object using
latex rubber molds.
You
can also shrink an object in three dimensions by using
gelatin molding compound to cast a duplicate of the
object, and then allowing the water in the compound
to evaporate. As the water evaporates, the size of the
casting will decrease evenly. This is very much like
the "shrunken heads" you may have seen where
someone carves a head from a fresh apple, and then leaves
the apple to dry out, creating a distorted, shrunken
version of the head. Using gelatin molding compound
allows you to better control the shrinkage, and allows
you to "shrink" existing objects instead of
having to carve them anew each time.
More
information and sources for gelatin molding compound
are in the Moldmaking Guide. One brand is "Instamold"
from Activa
Products.
Here is the complete procedure to make a shrunken copy
of an object:
1)
Make a mold of the object you want to shrink. Latex
rubber molds are easy to make and will allow you to
make a mold of an object with undercuts. You can also
use Gelatin Molding compound to make a very quick mold.
The "new" Gelatin Compound you use to make
the casting will not stick to the cured Gelatin Compound
in the mold.
2)
Use Gelatin Molding Compound as the casting material.
Mix the compound as follows, according to how much you
want the casting to shrink:
|
Powder Amount
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Water Amount
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Shrinkage
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Shrinkage Factor
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1 part
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1 part
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least
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.75
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1 part
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2 parts
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medium
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.65
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1 part
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3 parts
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most
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.55
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The
shrinkage factor times the original size of the object
is the approximate size of the gelatin casting after
it is allowed to shrink. For example, if your original
object is 4 inches tall, and you make a casting with
gelatin compound mixed 1:3 with water, when all the
water evaporates from the casting the shrunken gelatin
will be 4 inches x .55 or about 2.2 inches tall. The
more water you use to mix the gelatin compound, the
more your Gelatin casting will shrink, and the more
it will distort as it shrinks.
3)
Pour the mixed gelatin compound into your mold, and
let it set. When the casting is firm, remove it from
the mold.
4)
Set the casting on some paper towels and leave it in
the open to dry out. It may take 2-3 days to completely
dry out. If you want to speed the process, you can put
the casting in a microwave for 30 seconds or so. Watch
the gelatin, and as soon as it starts to steam, turn
off the oven. You can repeat this procedure over a period
of a few hours until the casting is mostly dry. Another
alternative is to put the casting in an oven turned
on very low (about 175º F) and leave it for a few hours.
5)
The gelatin will shrink quite evenly in all dimensions,
and should make a good, but smaller, reproduction of
your original object.
Gelatin
castings that shrink a little bit (a 1:1 mix) will generally
be more accurate than those that shrink more. Gelatin
castings that shrink a lot (a 1:3 mix) may have some
distortions or warped areas.
If
your dried, shrunken casting is warped or distorted,
it is easy to fix:
High
spots can easily be carved down with a sharp knife,
or sanded with sandpaper.
Low
spots or air pockets can be filled with wood putty,
clay, or spackle.
6)
Once you have a good casting in the size you want, give
it a couple of coats of clear spray sealer such as "Krylon"
clear acrylic spray. Then you can make a rubber mold
of the shrunken casting and make as many reproductions
as you want, in the material of your choice.
7)
If you want an even smaller casting, you can repeat
the process as many times as you want - make a mold
of the shrunken casting, cast gelatin into the mold
and allow the casting to shrink, make another mold,
and so on.
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