How Do You Make A Negative Mold For Fiberglass?

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Fiberglass is a common casting material, often used to make exact backup copies of props in stage and film, since a prop can be easily damaged. The best material for a casting fiberglass from a negative mold is plaster, made from mixed gypsum and water, and the best method is a two-part mold, so that the fiberglass halves are attached at the last stage. To make your own negative mold for fiberglass, read the instructions in this article. Coat the object that you would like to make fiberglass copies of in a mold release agent. If you are working from a soft clay sculpture, coat the sculpture in Krylon Crystal Clear or another clear sealer first, then let it dry before applying a mold release agent. This will protect the clay. Mark out the dividing line of the sculpture or object, from one side of the base to the other. Along this line, build up a wall of modeling clay that is at least as tall as you would like your mold to be. This way, you can pull your plaster mold apart with ... more
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