I am currently exploring the process of making paint from natural materials. I have started studying the (very time consuming) process of extracting pigment from different colors of dirt. I collect samples in zip-lock bags while traveling. The soil must be sifted, washed, filtered, and dried completely to separate the pigment from the sand and clay.
Then the pigment is ground, filtered again, and ground extensively with oil (linseed, poppy, or walnut oil) using a glass muller.
I like the idea of making oil paint the way the Old Masters did - using only natural materials, nothing synthetic or toxic.