After using plaster of Paris to create a molded sculpture or mixed media piece, you need to use a specific method to paint it. The absorbent quality of the plaster of Paris can cause paint to soak right in, so you need to prepare the plaster and apply the paint in a certain way.
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Prepare and Prime
Once you finish your plaster of Paris sculpture or mixed media project, allow it to cure, harden and dry completely before you begin to paint it. Attempting to paint wet or soft plaster of Paris could result in a ruined art project and a giant mess. Prime the plaster of Paris by applying acrylic gesso to the exterior using a paintbrush. Priming with gesso seals the plaster so it no longer absorbs moisture. Allow the gesso to dry completely, and apply a second coat if necessary.
Apply the Paint
Decorate your plaster of Paris sculpture using acrylic paint. Acrylic dries very quickly and you can apply it in layers, making it the perfect paint for plaster of Paris. Use paintbrushes, cotton swabs, sponges and even toothpicks to apply the acrylic paint however you want, to complete your plaster sculpture. Allow the paint to dry for at least 12 hours before displaying the project.
Dying Your Plaster of Paris
If you want to dye a batch plaster of Paris before you pour it into your mold or apply it to a mixed media project, start by mixing together 1 part water with 2 parts plaster of Paris in a large bucket. Stir the mixture continuously while adding in acrylic or tempera paint -- use as much paint as you want to achieve the color you need for your project. Once it's thoroughly combined, pour or apply the plaster of Paris as usual.
Tips and Warning
Lay down a sheet of painter's plastic or a disposable tablecloth before painting the plaster of Paris sculpture, to avoid getting paint all over your floor or table. Always keep curing plaster out of the reach of children because as it cures it will become very hot.