General procedure for earth pigments:
Grind up a rock that's good for pigments such as ochre. Now you have a mix of chunks- some are like tiny rocks, some like sand and some as fine as talcum. Your problem now is to separate out all the talcum sized bits. Put the ground up rock in a jar with water and shake. When you're done shaking, all the particles are suspended in the water and over time they will settle out. The big bits settle out first, then the medium bits settle out. If you wait a few minutes, everything settles out except the tiny bits. So, you pour off the water and tiny bits, leaving the bigger bits and some water in the first jar. In the new jar, you now have water plus tiny bits. Pour this onto a tray to evaporate the water. Once dry, you can heat it to change the color. The dry pigment is mixed with dilute hide glue to make a paint.
