Once upon a time, men would travel to far off lands in search of lapis lazuli. They'd carry the rocks back home and then grind them again and again, hoping for the tiniest amount of pure, clear pigment. Worth a king's ransom, it was reserved for painting only the most precious subjects and decorated only the most expensive goods.
For more on pigments (from a woman as obsessed with color as I am) check out Color: A Natural History of the Palette. Great book.