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. 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. 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. Like any product of nature, all cultured pearls have imperfections.