Artificial rock creation involves shaping materials such as paper mache, foam or styrofoam to mimic natural rock. The elements that make an artificial rock a convincing replica of an actual rock include irregular shape, natural colours and believable texture. An effective paint job on an artificial rock gives the appearance of surface irregularities and dimension. With basic tools for applying paint to artificial rocks and a selection of paints, you can create a realistic paint job to bring your artificial rock to life.
Select paint colours to create the type of rock you desire. Choosing more than one shade of each colour---or blending the colours yourself---helps to create a textured appearance. For example, to duplicate the effect of stripes of sediment in red sandstone, use a dark rust and a light rust paint.
Cover the work surface with newspaper. Set out the paints, containers and sponges.
Paint the artificial rock with white first. Dip the paintbrush in the white paint. Stroke the paint across the artificial rock using even strokes. Continue to cover the artificial rock. Allow the primer coat to dry.
Pour a half-dollar-size pool of each colour of paint into your containers. Mix needed colours, such as white and black to make grey. Mix the paint with an old butter knife.
Dip a sponge into the main colour you chose for your artificial rock, such as dark grey. Wipe the sponge at the edge of the container to remove excess paint. Press the sponge onto the artificial rock surface. Because of the holes in the sponge, the paint will go on in irregular patterns.
Repeat this process to add the first colour all over the top and sides of the rock. To keep from smearing the paint, leave the underside of the rock unpainted for now. Allow the paint to dry.
Dip a fresh piece of sponge in the second colour. For example, the artificial rock will be dark grey with a pattern of lighter grey and white. Paint the artificial rock with the light grey paint by pressing the sponge lightly on all the exposed areas. Allow the second paint layer to dry.
Dip a third clean piece of sponge into the white paint and dab it on. Use the third colour sparingly, so that it highlights the rock and doesn't overwhelm the main colour. For example, apply light dabs on the most prominent parts of the rock. Allow to dry.
Flip the artificial rock over and repeat Steps 5 through 8.
To work on small artificial rocks, cut the sponges in half. Rocks a foot in diameter or more will be faster to paint with the full-size dish sponge. If the artificial rock is large or rounded, place it in a bowl to help stabilise it while you paint.