Purchase minerals such as manganese oxide, gypsum and iron oxide to create colors for cave painting. These minerals can be purchased from science, hobby and chemical companies to be mixed into paint. If you wish to only use materials that you can find outside, skip this step. If you decide to use store-bought minerals, mix 1 cup of each mineral with 1 tbsp. vegetable shortening in old containers to create each paint color.
Walk around outside with plastic bags to pick up dirt. Look for dirt that is different colors to use for a variety of paint. Keep the colored dirt separated in different bags so the colors do not mix. Use an old spoon to scoop the dirt out of the ground.
Remove chunky debris from the dirt and place one color in your mortar and pestle. Grind the dirt as finely as possible. Place it in an old container.
Place 1 tbsp. vegetable shortening into the container and mix it in with the dirt. This will create a paint-like substance. Vegetable shortening is a good substitute for vegetable oils and other animal products that would have been used to make cave paint in ancient times.
Mix the rest of your dirt colors in the same way in separate containers. You can also grind charred wood in your mortar and pestle to create a dark brown or black paint when it is mixed with 1 tbsp. vegetable shortening. Continue with your project once the paints are mixed, using paint brushes or your fingers to create cave paintings on stone.