Platinum cure silicone rubber is poured into the box to make a mold of the left arm. The silicone is mixed up and then placed in the vacuum chamber that can be seen in many of these shots. The vacuum chamber takes most of the air out of the liquid rubber, so that air pockets and bubbles do not become trapped in the mold. This would weaken the mold and cause casting flaws.
After the silicone cures, the half-molded piece is taken out of the box, and the dam is removed from it. Then a box is rebuilt around it, release agent is applied to the silicone, and the other half of the mold is poured. In this picture both arm molds are shown after pouring. The arm is completely encased in rubber, except for an access point where resin will be poured into the mold.
