Once the first part of the mold had cured, the other side was removed. This consisted of the bottom of the mold box and the clay that was used as a barrier. The master and the sprues remain in place in the first part of the mold.
I use Vaseline as a separating agent between the two mold parts. RTV silicone will stick to itself really well, so a barrier cream is vital, at least on the rubber itself (most other materials are fine with silicone). I had some really old silicone that I was diluting with some silicone thinner, so these were definitely not ideal mold-making situations. Hopefully at some point in the future I can offer some examples of a more professional approach.
This picture shows the other component of the Ambull, the legs and back of the upper body. Same concepts applied: LEGO box, clay wall around the master, sprues cut from wood (found the dowels to be a bit better than the square stock). The little divots in the clay were pressed in with the back of a paintbrush. Once the rubber is poured in, they will serve as pegs to register the front and back parts of the mold.