The term "Black Pearl" describes any Pearl
that is dark in color. There are two kinds of Black Pearls that are available. One is the naturally-colored, more expensive black or Tahitian Pearl. It is found in the pinctada margaritifera
, also known as the large, black-lipped oyster, and is primarily found in the South Sea ocean waters around French Polynesia and the Cook Islands. The other type of black Pearl is an inexpensive Pearl that was originally white but has been dyed or irradiated
Neither of these black Pearls are what would be considered a true black, as the body color in a black Tahitian Pearl can be black, blue, gray, green, or brown, with overtones of pink, blue, gold, red, gray, reddish-purple, or yellow. The characteristic iridescent
sheen from the lustrous surface of either of the dark Pearls shimmers like oil on pavement. Variations in these body colors and overtones lead to an impressive pallet of possible colors, with peacock overtones among the most valuable.
The black-lipped oyster, named for its black tipped mantle and black edged shell, is usually six to eight inches in its pearl-growing phase, and around three to seven years old. However, black-lipped oysters up to a foot wide and as old as thirty years have also been observed.
The black-lipped oyster emits a dark colored pigment during the nacre
-building phase of the Pearl’s formation, leading to its hue. These Pearls are silver, gray and charcoal, with pure black an extremely rare occurrence.
The cultured Tahitian Black Pearl can be round, semi-round, button, circular, ovoid, teardrop, semi-baroque or baroque in shape.
Manufactured Black Pearls, which begin as white pearls, are either irradiated
with gamma rays
or dyed. Gamma rays darken only the nucleus in saltwater Pearls, leaving the nacre alone, giving the Pearl a gray or blue coloration. The same treatment for freshwater Pearls renders them very dark. Irradiation enhances the orient, or iridescence
of the Pearl, and the radiation is not retained, so the jewelry is safe to wear.
French dying is another method of turning white Pearls black. Silver nitrate is used to create a chemical reaction leading to the black color.
Neither dying nor irradiation can be considered a permanent treatment and the Pearls can fade over time. Reputable dealers will inform their customers of any treatments that the Pearls have been given. Natural Pearls will vary more than treated Pearls. Pearls in a strand that match too well and look too consistent were probably treated. Sighting down the drill hole of a pearl may show a darkened nucleus which would indicate irradiation treatment. Concentrations of color may also be seen, which would mean the Pearl was dyed.