Measure out the amount of plaster of Paris needed to make a mold. The general use for most brands of plaster of Paris is 1 part water to 2 parts plaster, with a yield of approximately 1 1/2 cups of the finished product.
Pour water into the mold to the level you want the plaster, then measure it out in cups. For instance, if you want to make a mold of your handprint in a pie plate, you would pour water in to the depth you want. If you used 4 1/2 cups of water, you would then need to use 6 cups of plaster of Paris and 3 cups of water.
Measure out the dry plaster into a plastic bowl and make a well in the middle. Pour in the water all at once, and stir until the mixture is smooth.
Pour the liquid plaster into your mold slowly, starting with the lowest areas and filling in all the spaces. Use all the plaster you prepare, as it doesn't store well.
Allow your plaster of Paris mold to sit undisturbed until it hardens. Carefully loosen the edges, and allow the plaster to fall out. Make sure you catch it.
Use prepared plaster bandages to wrap around fully inflated balloons to make easy pinatas. Dip the pre-rolled bandages in warm water, allowing them to soften before wringing gently and unrolling onto the surface of the balloon. Use a single layer, and allow it to dry completely before popping and removing the balloon from the top.
Make free castings by pouring mixed plaster into animal tracks or other indentions and letting it harden.
Fashion small bits of jewelry by filling tiny plastic molds with plaster and painting the hardened objects to use on children's bracelets and chains.