Plaster of Paris molds are created specifically for casting plaster into specific sizes or shapes. There are companies that produce molds especially for use with plaster of Paris, and in a wide variety of shapes -- from school buses and animals, to stepping stones and religious symbols.
Plaster of Paris is a gypsum-based white powder that becomes a pasty substance when combined with water. It can be poured or sculpted while wet, and hardens to a solid creation. It is most commonly poured into a mold. The choices for laster of Paris molds are wide and varied.
These plaster of Paris molds are not the only option for casting, however. The smooth-drying nature of plaster of Paris makes it easy to use with almost any plastic mold. This greatly expands the size and variety of molds available to you. Soap molds, candle molds, and candy molds all work well with plaster. The smaller size of most candy molds make them perfect for creating small ornaments, for example.
Any casting can be modified while it is damp. After the mold is poured, allow it to dry for a few minutes. Press stamps or hand prints into the plaster while it is still wet. It should hold the shape of the object. If it does not, wait a couple of minutes and try again. This is a popular and simple way to preserve a child's hand prints and footprints, although does not allow for the detail that some prefer to have.
Another option for casting is to create your own plaster of Paris molds. One method of doing this is with sand. Place slightly damp sand in a shallow pan and press any object into the sand. For example, press a hand or other object into the sand and hold it steady until the sand holds the shape. Remove the object. Pour the plaster into the new print and allow it to dry. As with the pressing method, this method does not give a great deal of detail to the newly created plaster casting.
Another method to create plaster of Paris molds is to use clay. This method allows for a greater amount of detail on the cast and is preferred among most artists and those who regularly work with plaster. Any modeling clay will work well. Lay out the clay on a flat surface and press the hand or other object into the clay. The plaster can be poured directly into the clay and allowed to dry. Once the plaster is dry, simply peel off the clay.