Plaster of Paris, sometimes called plaster, is a powder-based material that, when mixed with water, creates a material that hardens much like cement. Plaster of Paris is ideal for use with moulds and an excellent choice for relief-carving projects. Tools needed for relief-carving plaster of Paris are minimal. Plaster of Paris works well with most types of paints, allowing artists to apply a variety of techniques to create beautiful finished pieces.
Purchase plaster of Paris at a hobby or craft shop. Mix the plaster of Paris according to the instructions on the package. Typically, this will be one part water to two parts Plaster of Paris. Adding too much water will cause the plaster to crack.
Pour mixed plaster into a mould. Use a metal baking pan measuring 6-by-9 inches with a depth of at least 6 inches to give you room to bring out the relief effect of your design. You can use any type of mould, but this is ideal for a plaster relief carving. If you'd rather have a round carving, use a round baking pan as your mould. Use a knife or ruler to smooth the plaster flat, then let it dry for several hours (preferably overnight) before you begin working on your carving.
Remove your plaster from the mould. You may need to slide a knife around the edges to loosen it. Place your hand on the top surface and turn your mould upside down. Keep your hand in place as you shake the plaster piece from the mould. Place it on a sturdy, flat work surface for the carving process.
Draw your design onto the plaster with a pencil. If you can't draw by hand, there are plenty of stencil designs available at hobby and craft stores.
Use a flat chisel to remove the plaster from around the outside of your design. This will cause the design itself to rise from the background in relief. Cut low for a bas relief or dig deep into the plaster for a high relief design. To work on more intricate details on the design itself, you will need to use an X-ACTO knife with a small, sharp tip. You can also purchase a set of various size chisels at a hobby store.
Sand your design with a light-grit sandpaper until it has a smooth finish, then brush away the excess plaster dust before you apply paint. Use acrylic paints to colour your relief design. Allow the paint to dry, then use a spray gloss coating to give it a shiny finish.
If you're just starting with relief carving, start with a design that won't require cutting away too many small details. The goal of relief carving is to remove extraneous background plaster to cause your design to rise away from the plaster background.