Plaster hardens into a hard, white substance.
Artists have long used pottery plaster for casting and mold making, particularly for making slip molds for ceramics. However, you can use it with any number of different materials. Pottery plaster comes as a fine white powder that, when mixed with water, chemically changes and hardens into a rigid shell. When making a plaster mold of a figurine you will need to create two shells of the front and back of the figurine that fit together.
Instructions
1. Lay down three layers of newspaper and don a pair of gloves and a face mask. Create a rectangle out of plasticine that is deep enough and large enough to embed your figurine into and set it on the newspaper.
2. Embed your figurine halfway into the plasticine. Beware of any undercuts or protrusions on your figurine. These will cause your figurine to become stuck in the plaster shell and you will find it almost impossible to remove. You may avoid problems by tilting the figurine when you embed it so that the protrusion rests on the very top of the plasticine bed. However, you will not be able to accommodate too many protrusions going in different directions.
3. Embed four marbles into each corner of your plasticine bed. Cover the marbles and the figurine with liquid wax. The wax will act as a mold release and keep the plaster from adhering to your prototype too much.
4. Fill a bucket with pottery plaster powder, enough to potentially cover your figurine. Put it under a faucet and begin to fill the bucket with water. Stir the plaster with your gloved hands as it fills. Turn the water off when the plaster reaches the consistency of thick mud.
5. Return quickly to your figurine and use your hands to dab the plaster over the surface of the plasticine bed. Make sure that the plaster is at least 1 inch thick at any given point. Let the plaster harden overnight.
6. Flip the mold over and peel the plasticine away from the plaster to reveal the figurine and the marbles. Remove the marbles but leave the figurine in place. Rub the newly exposed side of the figurine and the plaster around it with liquid wax. Let liquid wax dribble over the sides of the plaster shell.
7. Mix up a new batch of pottery plaster exactly as you did before. Apply it to the second half of the figurine and allow it to harden overnight.
8. Separate the two halves of the mold and remove your figurine. Rinse the inside of the plaster to remove the liquid wax residue. Allow the two halves of the mold to dry for a week before using them.
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