| You might find this helpful (on pg. 556 of Strack's book, emphasis added, in the section discussing Tahitian cultured pearls):
“The iridescence of Tahitian cultured pearls always appears as an overtone which seems to float on the surface of the pearl in the shape of a circle. The overtone consists of one, two or three almost transparent colors, which stretch over the circle. They can be seen most easily if the observer looks across the shining, reflecting surface directly into the surface layers of the pearl. Orient is not found in Tahitian cultured pearls.”
Perle |