Page 111 - Casting of Angels- Dave Parvin

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Great Mold Part II

David E. Parvin, A.L.I.

hen I began writing on this MG is especially ideal for layered
subject, I thought that it would applications. Other materials require
take two articles. But as it you to mix a batch, apply it, let it
turns out, it will take three. It thicken, then mix another batch and
isn’t that it is so difficult but rather that repeat until you have a sufficient
there are many small steps that need to thickness. Forton MG is so much
be explained. While this may seem easier because you can mix the entire
unnecessarily complicated and lengthy, amount that you think you will need,
the resulting flawless castings will dump just enough for one layer into a
make it all worthwhile. In “Great Mold separate container, add an accelerant
Part I,” SJ , Nov. 2006, I explained Photograph #13 which will cause just the separated

attaching the model to the base, amount to set up quickly, apply, and
covering the model with clay, and was then repeat with the next layer. The
almost finished with building the accelerant is a solution of 10 parts
mother mold. In this article, I will aluminum sulfate to 100 parts water.
complete the mother mold. Next month, Aluminum sulfate is a fertilizer
I will pour in the rubber, finish the available anywhere that sells gardening
mold, and put the mold to use. supplies, and, compared to many of the
products that we artists use, is cheap. A
Building the Mother Mold tablespoon of accelerant to a pint of
Photograph #14 Forton MG will cause it to solidify in
At the end of last month’s about 10 minutes. The amount of isn’t
article, I was almost ready to spread on critical, just be aware that the more you
what would become one side of the use, the faster the reaction. In
mother mold. The only thing remaining photograph #13, I am painting a coat of
was to apply a mold release. A great plain Forton MG over the clay and the
release is a solution of 15 parts by metal shim. Next, not shown, two thin
weight of petroleum jelly to 100 parts coats containing chopped fiberglass
naphtha. The petroleum jelly doesn’t fibers were added. In photograph #14
dissolve very quickly and I would assistant Morgan is finishing up with a
suggest mixing the two at least a day Photograph #15 final layer of plain Forton MG to give
before needed. Applied with a soft paint the outside of the mold a smooth finish.
brush, the naphtha will quickie dissolve As soon as the last layer of Forton MG
leaving a thin, even layer of petroleum has set up, give it about 30 minutes, it
jelly. This will not only facilitate is time to repeat the process for the
separating this first side of the mother other side.
mold from the clay and shim but will The thickness of the mother
also smooth out the clay. I learned of mold will depend on what it is made of.
this release solution from Michael With most of the materials mentioned
Sisbarro who is another contributing above, including Forton MG but not
writer to Sculpture Journal and have plaster, no more than 1/4 inch (about
found it to be an excellent all around 1/2 cm.) is sufficient. Be sure to bury
release agent and I always keep some the threaded metal inserts up to their
made up. tops. Don’t worry if the tops get
The next thing was to decide on a covered, the clay that was pushed into
material for the mother mold and there Photograph #16 the ends should keep the threads clean.
are lots of choices such as In photograph #15, I am
plaster, FGR-95 Hydrocal, see my article, “Mixing Forton removing the metal shim. Notice the
polyester and polyurethane resins, fiber MG Simplified,” SJ, July 2003.) ends of the threaded metal inserts and
glass, epoxy, and Forton MG. I prefer But applying the material over the small indentations from the plastic
the latter because Forton MG is easy to the clay is done approximately “feet.” These indentations will assure
use, odorless, water soluble, the same way regardless of that the two sides of the mold align
inexpensive, and very strong allowing which is used. Since all of these perfectly so that the bolts will fit easily
for thin molds that are light in weight. materials are liquid, all are and properly into the inserts. Also
(For more information on Forton MG, applied in layers. But Forton notice that the clay dam that had
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