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The next step is to coat the inside of the box and the jig pattern itself with petroleum jelly to prevent the plaster from sticking. A thin coat is all that is necessary. Now mix some of the plaster of Paris or water putty in a container with water. You can do this with a stick but your hands are much better for breaking up any lumps. Keep adding water and plaster until you get a heavy consistency one which still pours freely, however. And be sure you make enough to fill the box half full. Now pour this plaster into the small box until it is half full. Then sink your jig pattern halfway into the wet plaster. You should allow a space of about ? in. between the rear end of the jig and the box side and 1 in. from the opposite end of the box side to the jig. See Fig. 87. Figure 87. Position of jig pattern in mold box. Next, sink two flat-headed nails into the wet plaster, allowing about in. of the pointed ends to project. They can be placed diagonally opposite near the corners. They will act as locating pins when using the two mold halves when casting. See Fig. 88. Figure 88. Position of nails which act as location pins.
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