When you are creating a sculpture using plaster of Paris, it is traditional to create moulds using cardboard, wood or metal. Molds can also be create for the plaster using common household items, such as balloons. When you make a balloon mould, then finished plaster sculpture can be formed into rounded shapes that will be free of sharp edges that need to be chiselled or sanded off. Make a balloon plaster mould using a few basic craft materials.
Insert a small funnel into the opening of a balloon. Select a heavyweight balloon so that it can hold the weight of plaster of Paris.
Combine 2 cups of plaster of Paris and 2 cups of water into a spouted bowl. Stir the mixture for two minutes using a spoon to combine the materials completely.
Pour the plaster of Paris into the balloon through the funnel. Fill the balloon until it is full up the base of the balloon opening.
Remove the funnel and tie the opening of the balloon into a tight knot.
Mold the plaster-filled balloon to the shape you prefer, then allow the balloon to sit undisturbed for four hours. Cut off the balloon to reveal the rounded plaster casting.