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I have been experimenting with molding and casting costume parts and can now
share my experiences with my readers. I don't consider molding and casting to be
easy or quick, but if you want several copies of the same costume piece, then this process
can be rather rewarding.
If you read this section and are interested in this, I recommend Thurston James' The
Prop Builder's Molding and Casting Handbook. Also check out Jeff Allen's How to Build Stormtrooper
Armor. He has a good guide to plaster mixing and mold making.
SAFETY FIRST! Use the latex rubber in a well ventilated area. Wear a dust mask
when working with the plaster or Water Putty to keep from breathing the fine particles of
dust.
Now let's start with a couple of definitions.
The cast is the finished product that we want.
The model is something we build that we want several copies of.
The mold is a 'negative' of the model, think of a Jell-O mold.
Slush casting is using latex rubber as a flexible casting material (like a
Halloween mask). This is best done with a gypsum mold like plaster of Paris, or
other more expensive materials like Ultra-Cal.
Mold release is a substance you put on to free someting from a mold. This can
either be petroleum jelly to release a model from a plaster mold, or talcum powder to
release a latex casting from a plaster mold.
Here's a rule of thumb for molding and casting, if you want a hard, rigid casting, make a
hard model and use a flexible mold to make the hard casting. On the other hand, if
you want a flexible casting, make a flexible model and use a hard mold to make the
flexible casting. All of the times I have failed in the past, it was because I tried
to get around this rule.
The materials: I get latex rubber and oil based clay from Monster Makers, the plaster of Paris and the rest
come from hardware stores (you can get a 25 lb bag of plaster of Paris for about $8).
The best way to show how this works is by example, I'll describe how to make a flak vest
and chest box.
FLAK VEST
First, take a look at the picture. The brown thing
in the center is the model, the white thing on the left is the plaster mold and the last
thing is the latex rubber casting (the picture makes it look uneven, but it is just fine).
Build the model from cardboard and oil based clay. Next, build a retaining wall
around the model from cardboard and duct tape. Smear petroleum jelly all over the
model, and the inside of the retaining walls, everywhere that is going to come in contact
with the plaster. The petroleum jelly is a mold release.
Mix a batch of plaster and pour it on the model. Tap the side of the model's base to
jar loose any bubbles. Let the plaster harden (an hour) and pull the model away from
the plaster mold. Clean all of the petroleum jelly off of the mold with some rubbing
alcohol and towels. Do a good job with this - latex rubber does not like petroleum
jelly.
The cast will be made from latex rubber and will require a dry mold. Let the mold
sit for at least a week. When ready to make the casting, use a makeup brush to
lightly dust the surface of the mold with talcum powder for a mold release.
Pour the liquid latex into the mold. Let it sit until the latex starts to develop a
skin (20 minutes? It will depend on the dryness of the mold, the viscosity of the latex,
and temperature). If you want a thicker casting, let the latex sit longer.
Pour the excess latex back into your jar - you will get to use the excess amount next
time.
Let the latex sit in the mold for 24 hours to cure. Curing time will depend on the
thickness of the latex, the dryness of the mold, and temperature. You can speed up
the curing time by having a fan blow over it. When dry, peel the latex casting
carefully from the mold. |
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