Among commercially farmed pearls, Tahitian pearls are considered the second most valuable pearl in the world. Tahitian pearls come by their dark color naturally, unlike black freshwater pearls and black akoya pearls, which are dyed or irradiated to make them black. Pearls from Tahiti are bead-nucleated, but the nacre on these pearls is typically thicker than akoya pearls. 0.8 mm is the thinnest nacre permitted by French Polynesian law for export, which would be considered extremely thick in akoya terms.