Things You'll Need
Mold release agent
Plaster of paris
Plaster of paris is a great material to use for creating exact replicas using flexible molds. Inexpensive and easy to mix and pour, plaster of paris can recreate exact details and dries solidly. It's also modifiable through additives to create a variety of colors and textures. Plaster of paris can damage a mold if precautions are not taken to prevent the substance from sticking to the mold's surface. Fortunately, this problem is easy to solve with a few short steps added to the casting process that will leave your molds in good condition for reuse without affecting the quality of the plaster cast at all.
Spray the mold's surface with a mold release agent purchased at most art supply stores or hobby shops. The mold release agent will form a layer between the plaster of paris and the mold that prevents the plaster from sticking to the mold's surface. Only a light layer of release agent will be required.
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Mix the plaster of paris with the water in a plastic cup with a plaster to water ratio determined according to the manufacturer's instructions. The plaster should form the consistency of pancake batter.
Coat the mold with talcum powder to help remove any air bubble formed when pouring the plaster into the mold. The talcum powder also aids in keeping the plaster from absorbing all of the moisture from the mold itself.
Place the mold onto a piece of stock foam board laid on a level surface.
Pour the plaster of paris into the mold, filling the cavity of the mold completely.
Lightly pound on the foam board to vibrate the plaster, raising any air bubbles to the surface of the poured plaster. Continue until the bubbles cease to rise and then wait for the plaster to set.
Remove the hardened plaster of paris from the mold once it's set. The mold should easily peel away from the plaster with the release agent sprayed onto the mold preventing the plaster from sticking.
Pour the dry plaster into a plastic cup and then use the cup to pour the plaster into the water when mixing. The cup helps you to control the amount of plaster added easier.
When dealing with larger molds, wear protective clothing as plaster heats when it setting and can cause burns if left on skin.