making plaster molds

Molds don't have to have more than 2 pieces unless they would have undercuts that would prevent the clay from coming out. So for example a hand might be a 2-piece mold, if the hand was open flat and the parting line was exactly halfway through the thickness of each finger. But sometimes it is easier to just make a multi-part mold than to try to figure out how to make a 2-part mold that will work.

Note that plaster releases heat when it sets, so it's not a good idea to use it directly on skin. You might want to press your hand in a big slab of clay, make a plaster model from that, and make the mold from the plaster model. The advantage is that pressing into soft clay makes it easy to see where the parting line will be. Soft clay needs no release agent, just pour the plaster over it directly. Of course, you will need a wall ("cottle") around the slab to keep the plaster in place. You can make the slab in a plastic bucket or rectangular freezer container, etc, and no release agent is needed there either. But you will need release agent between your plaster model and the plaster mold. Soap is the old standby, such as Fels Naptha or Ivory made up into a thick solution and painted on. Don't use liquid dish or hand "soap", since these are really detergents.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis