When selecting bead-nucleated pearls, the buyer should consider nacre thickness for two important reasons. First, the thinner the layer of nacre, the more prone the pearls surface is to cracking and peeling and exposing the bead that lies beneath. Second, nacre thickness determines a pearls luster, or bright iridescence. A thicker layer provides greater luster.

 

Color Variations

 

Pearls occur naturally in a spectacular array of colors. A pearl's color depends on both the species of mollusk that produced the pearl and the environment in which the animal lives and the pearl is grown. In general, the crystals of aragonite comprising the nacre are white or colorless. A pearls color is mostly due to the conchiolin layers, which contain organic pigments.

 

The saltwater Akoya oyster produces a white pearl that can express a slight green, silver, or rose tone. South Sea saltwater pearls generally come in silver-white and gold, produced from the silver-lipped and gold-lipped oysters. Tahitian blacks come exclusively from the Tahitian black-lipped oyster. A black pearl from any other source is presumably an artificially dyed product.

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Freshwater pearls come in a wide range and gradation of colors. The great majority of todays production is grown in China using the large cockscomb mussel. This mussel produces white pearls of silver, green, or rose-tones as well as natural lavenders and coral-colors ranging from soft to vivid.

 

To learn more about natural and cultured pearls, the American Museum of Natural History has an excellent exhibition