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Robert Oblon
Joined:
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04-Aug-2004
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Started On : 28-May-2009 at 11:59:35 PM, #Views : 6964
Topic Subject : Re: Re: Copying Castings |
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Clay
What you are referring to are registration keys. The keys are used when
making a two piece rubber mold some time called a book mold or brush up mold.
We use clay as a shim at the parting line (one half of the sculpture that
allows two mold halves). We build a box around the clay wall (shim) and then
create "registration keys" using the head of a screw driver pressed into
the clay shim. We then mix our silicone rubber brush on our "print coat" and
then pour an amount into the box and continue to brush or "pull" the
rubber until it sets in about an hour. We use Silicones Incorporated GI 1000
silicone. I try not to use an accelerator due to the fact that it shortens the
shelf life of the silicone rubber mold and makes it brittle too. Once the
first side of the rubber has cured we mix up hydrocal FMG-95, adding
fiberglass strands to make a mother mold over the silicone rubber half. Once the
hydrocal is set, we strip the box flip over the mold, strip away the clay
shim, check the surface of the second half of the sculpture, box up the
mold, apply a mixture of dish soap cut 50% with water to the exposed silicone
shim, mix rubber and proceed as we did to the first half of the mold. I know
that was a very long run on sentence. So the screw driver head impression
that we created by pressing the screw driver into the clay has become a
positive registration key in silicone that will now have the second half of
the rubber poured onto it and the sculpture. Once the second half has cured
along with the hydrocal mother they are removed from the box walls and the
two halves of the rubber is stripped away from the sculpture creating a
negative void where the sculpture was, the two halves are put back together
using those "registration keys" that are part of the silicone rubber mold
structure and backed by the mother mold help in place with strapping. Molten
pattern was is poured into the opening that was created when the sculpture
was first laid up with clay. Our silicone rubber molds are used to create wax
patterns for ceramic shell casting that we do in silicon bronze and
stainless steel. These same molds can be used for liquid plastics, plaster
castings, etc.
Cheers
Robert Oblon
Central Coast Art Foundry
Arroyo Grande, California
805-748-5381, Fax 805-980-4890
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