you grind pigments with distilled water into a paste, you can store them like that in jars.
when painting you will need to prepare paints by mixing pigment paste with water (just as much as you would use in a painting day) and adding a little lime for consistency (half a teaspoon of pigment paste + coffee bean of lime).
Lime is also used as white pigment for fresco.
grinding pigments article:
fresco pigments set:
learn fresco at http://FrescoSchool.org
fresco painting video tutorials: http://www.FrescoSchool.com
Fresco School Video Channel
Contemporary Fresco Gazette
commission fresco or mural http://iLAdesigns.com
Contemporary Fresco Painting Resouce Center