Plaster of Paris is one of the most popular materials used in casting. It dates back centuries and is preferred because it is inexpensive and durable if taken care of properly. Plaster can be used as the negative or positive in a mold and works well with a release of petroleum jelly. To speed up the process of casting body parts, some artists use dental mold material for the negative cast, which allows for greater detail, and then plaster of Paris for the positive mould. Plaster comes in either powdered form to be mixed with water or in strips of gauze that are embedded with plaster powder. Slowing down the curing time of plaster of Paris can be achieved by using cold water, which makes it slower to set. The warmer the water, the faster the setting time.
Instructions
1. Cut strips of plaster of Paris gauze prior to casting. Cover whatever is being cast in petroleum jelly so that it can be released easily. If you are casting a body part with hair, consider shaving the area that will be cast.
2. Fill a bucket with cold water to slow down the curing time of the plaster of Paris.
3. Create a plaster mixture for a molld: Using your hand, sift powdered plaster by the handful into the bucket of cold water; it will sink to the bottom. Continue doing this until the powder remains at the top of the water for at least 5 seconds before sinking.
4. Use your hand to quickly mix the the plaster on the bottom of the bucket with the cold water, breaking up all chunks with your fingers as you go. Your hand should have a thin coating of plaster stuck to it when you finish mixing.
5. Pour mixture into your mold immediately. Gently tap the bottom and sides of the mold, releasing air bubbles as you pour, and again after the plaster is completely poured.
6. Create a cast using plaster gauze by dipping the impregnated plaster gauze into cold water and gently run it between your fingers, making sure to activate and moisten all of the powder. Place strips on top of whatever you are casting.
7. Allow at least 10 minutes for plaster to harden before releasing a mold or removing a cast.
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