Unnatural Blondes

Susan Wade writes:

http://www.tucsonshowguide.com/stories/nov02/goldpearl2.cfm

Like most gems, pearls have a long history of modification and "improvement" by humans. Most in the pearl industry agree these treatments should be disclosed to buyers, but admit that such disclosure isn't always as complete as it should be.

Pearl treatments range from the accepted practice of bleaching to the almost universally disliked process of adding a polymer coating to improve the luster. In colored pearls, one of the greatest concerns is the alteration of the color. Pearl color is most commonly altered in one of three ways: irradiation, dyeing, and heat treatment.

Irradiation gives pearls a gray color, although the exact shade depends on the type of pearl involved. In freshwater pearls, the entire pearl turns black to gray. In cultured saltwater pearls, it's generally only the shell bead in the center that's affected by radiation, turning a black that shows through the nacre and causes the entire pearl to appear dark gray or black. These treatments are usually detected by ultraviolet (UV) spectroscopy, or by microscopic examination of the drill hole, which will reveal the disparity between the surface nacre and the shell bead.