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The first step is to create the clay platform that we will use to embed half of the coin.
Enough clay strips are cut to comfortably support the model and give sufficient wall
thickness to the finished mold. The strips are put together and seams are joined and
smoothed. A rolling pin is then used to level and smooth. A straight edge is used to create
clean edges that will align nicely in the mold box. One half of the coin model is embedded
in the clay, up to roughly the midpoint of the coin's side edge. The hex nuts are partially
embedded and will serve as registration keys to lock half the finish mold to the other
half. The mold box sidewalls are positioned and secured around the clay foundation using
clamps. A glue gun is then used to seal the seams at the interface between the mold box
sidewalls and the baseboard. The next step is to create a pouring vent that will allow
us to pour a casting material into the finished mold, and an air vent that will allow air
contained in the mold cavity to escape during casting. A small piece plastic tubing this
measured and cut. The pouring vent will extend from the mold box wall to the top of the model.
One half of the piece of tubing is then embedded in modeling clay. The vent is also embedded
in clay. The next step is to apply release agent made especially for using with silicone rubber.
Parts A and B of the silicone are measured out in equal amounts, dispensed into a mixing
container, and mixed carefully. By the time you are done mixing, the rubber will be a
uniform color with no streaks. The rubber is then poured in a slow, steady stream at
the lowest point in the mold box and allowed to rise over and above the model. OOMOO rubber
cures at room temperature. In about six hours, it is ready for demolding. The next step is
to remove the clamps and mold box sidewalls, and the mold structure is then flipped over. The cured
rubber with the model still partially embedded is now resting on the platform. The clay foundation
is then removed, exposing the hex nuts and one half of the coin. The hex nuts are removed
leaving holes that are now the negative registration keys. The excess rubber is trimmed, taking
care not to disturb the model. The mold box is then reassembled securely around the cured
rubber with half the coin model still embedded. Hot-melt glue is used to make sure that the
liquid rubber will be contained. As before, OOMOO silicone is mixed carefully. The mixture
is then poured over the first half of our mold. The rubber is allowed to cure at room
temperature, and the mold box sidewalls are removed. The mold halves are then separated,
and the model is removed to reveal the negative mold cavities that reflect perfect detail
captured from both sides of the model. The mold halves are brought together and secured
using the registration keys. Rubber bands will help hold everything in place and minimize
leakage of liquid resin during casting. A small amount of Smooth-Cast 300 Part A and
B is dispensed in equal amounts. To give the finished casting a little color, a couple
of drops of SO-Strong color tint is premixed with Part B. Parts A and B are then mixed
thoroughly for about a minute. The mixture is then carefully poured into the pour vent.
The mold is slightly rotated to displace air in the mold cavity, and more resin is added
as needed. Because this is a small amount of material, the resin is allowed to cure
for about twenty minutes. The rubber bands and then removed, and the mold halves are
pulled apart revealing the casting. The mold has reproduced detail from both sides of the
original perfectly. Excess flashing is then removed with a razor knife. We now have an
exact reproduction of our two-sided original.