Pearl size is mostly determined by two factors: the size of the implanted nucleus and the thickness of the nacre that grows layer upon layer around the nucleus. A large cultured pearl that lacks nacre thickness has a low value, and tends to discolor and crack fairly easily. A pearl with a thick nacre coating will retain its luster and beauty for a lifetime when properly cared for. For pearls of similar quality, the most important other determinant of price is the size of the pearl. The size is generally measured in millimeters.
Perfectly round cultured pearls are the rarest. Although most cultured pearls are nearly round, only about 1% is perfectly spherical. To check a strand for roundness, roll it across a flat surface. The strand should move evenly and smoothly.
Luster refers to the surface property that imbues cultured pearls with their shine and beauty. When checking pearls for luster, view them while standing with your back to a source of light. The sharper your reflection on the surface of the pearl, the higher is the luster and the better the quality.
Pearls come in a variety of shades, with the major classifications being white, pink, silver, cream, gold, and black. Choice pearls also have a secondary color, or “overtone”, around the surface of the pearl. These overtones are usually rose, green or blue. The color should emanate from deep within the center of the pearl. All the pearls in a strand should be consistent in color.
Just as with any product of nature, all cultured pearls have minor imperfections. A quality cultured pearl is free of large pits or blemishes.
Akoya pearls are cultivated using Pinctada Fukata oysters. Although most Akoya pearls are cultivated in Japan, they are also cultured in the tropical waters off the coast of Korea and China and southward as far as Sri Lanka. Akoya pearls are from two to ten millimeters in size, and their shape is typically round or off-round. Colors range from pink to white and yellow. Typically pearls are harvested after about eighteen months to three years of cultivation, reaching about 0.5 mm in diameter after eighteen months in the host oyster. Akoya pearls are renowned for their high luster and rich color.
Tahitian Black Pearls
Tahitian Black pearls are cultivated from Pinctada Margaritifera oysters (black lip oysters) found in French Polynesian waters. Black South Sea pearls come in a wide range of colors from silver / gray, blue, and red / eggplant to dark green, with peacock being the most valuable. Cultivation time averages about two years. Tahitian pearls have long been highly prized by many cultures for their exotic colors and brilliant luster.