You can purchase Plaster of Paris at a craft supply store, or you can easily make your own kid-safe version at home, work or school. Plaster dries easily in moulds and therefore can be used in many art projects, such as decorative pins, magnets, and hand and footprint crafts. Try adding food colouring to the plaster to make coloured sidewalk chalk or scented oils to make air fresheners.
Put on an art smock or an apron; making plaster can be a messy task. Cover your work area with plastic garbage bags to prevent having to do a huge cleanup later.
Pour 6 cups of all-purpose flour into a mixing bowl. Use a wire whisk to stir the flour and eliminate any lumps.
Add 4 cups of warm water to the flour, and stir gently with a spoon until the flour and water have combined to make a firm but smooth paste. If the paste is too runny, add more flour; if the paste is too firm, add more water. For variety, add food colouring or essential oils to the paste, and stir until combined.
Use the plaster immediately because it will firm up quickly and will no longer be usable.
If your plaster dries out, all is not lost. Use nails and other hard objects to etch a design into the dried plaster, and then paint it with craft paint.