When shopping for pearls, the five factors that determine value are luster (surface brilliance); surface cleanliness (absence of spots, bumps or cracks); shape (generally, the rounder the pearl, the higher its value); color (pearls come in virtually every hue of the rainbow, and a few others, too); and size (the average pearl sold is 7-7.5 millimeters, but these gems can be as small as 1 millimeter or as large as 20 millimeters). High-quality pearl strands will feature pearls well-matched in these characteristics.

Because pearls are soft, ranking only 2.5-4.5 on the Mohs scale for hardness, they require special care. Natural oils from the skin, as well as hair spray, lotions and cosmetics, can dull their luster. Like other jewelry, they should be cleaned with a soft damp cloth and stored in cloth or cotton away from other jewelry to prevent scratching. Also, avoid allowing your pearl to come in contact with harsh chemicals, which can erode its surface. And if worn frequently, pearl necklaces should be brought to a jeweler once a year for re-stringing to prevent strand breakage.