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Figure 24. The finished hand casting ready for displaying.
De-Mold The Cast. To de-mold, pull off the plaster bandages. They will be somewhat resistant to removal. This is often so. But if you are fortunate, the entire mold may come off at once. Either way you must remove the plaster bandages and the alginate mold underneath them. There is a caveat here. If you wait too long to de-mold, say overnight, it will be much more difficult to remove the alginate, because as it dries, it becomes hard and shrinks. So the ideal de-mold time is about four hours after you finish pouring the casting.
Once de-molded, inspect the surface of the casting. It is normal to find defects such as small wart-like dimples (caused by air bubbles). These can be easily popped off using a table knife. If you find indentations or craters (caused by air traps), fill them with a little Spackle. You may want to square off the ends of each of the arms. You can do so with a saw. Use a plaster rasp to remove any large defects followed by some light sanding.
Let the casting dry for at least forty-eight hours before applying paint or sealer. If you wish to leave it unfinished, then seal with polyurethane clear matte finish such as that offered by Krylon or Rustoleum. It is important that you seal the surface as plaster is hygroscopic – meaning it attracts moisture, which will eventually lead to a chalky surface. As you gain experience you will want to create your finished casting in cold cast metal, such as bronze, brass or copper as that finish always appears more elegant.
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