A pearl is the product of a partnership between nature and chance. When a foreign object, such as a grain of sand, is trapped in an oyster or mussel, it is coated with layers of a smooth, crystalline substance known as nacre. Over time, this natural process produces the luminescent gem we know as a pearl. Nearly all pearls sold today are cultured. That is to say, each one is created by deliberately inserting an irritant into the oyster's tissue. However, the quality of cultured pearls varies widely. Unlike diamonds, cultured pearls are not rated by an industry-wide grading system. As with diamonds, however, there are specific characteristics that do affect cultured pearl quality.
QUALITIES OF PEARL
More than any other factor, size determines price. Pearl size is the result of the size of the implanted nucleus plus the thickness of the nacre, which grows layer by layer. A large cultured pearl is of little value if it lacks nacre thickness since a thinly coated cultured pearl will crack and discolor. Nacre thickness can be verified only by an expert.
Perfectly round cultured pearls are the rarest. While most cultured pearls are basically round, only about 1% are perfect spheres. To check a strand, roll it on a flat surface. The movement should be even and smooth.
Pearls occur in a spectrum of shades. The major classifications are white, pink, silver, cream, gold and black. Fine cultured pearls will also have a secondary color or "overtone" — usually rose, green or blue — around the outside of the pearl. Traditionally, cultured pearls with pinkish-white or pinkish-silver coloring are the most highly prized. Whatever the color, it should appear to emanate from deep within the cultured pearl.
A small percentage of cultured pearls display rainbow-like colors that appear to move over the surface.
Luster refers to the surface shine that gives cultured pearls their glowing beauty. Stand with your back to the light; the sharper the reflection of light on the cultured pearl, the higher the luster.
Like any product of nature, all cultured pearls have imperfections. However, a quality cultured pearl should be free of large pits or blemishes.
Every pearl is unique. The type of mollusk and natural elements often combine to produce unusual shapes and colors.