As it is more difficult for oysters to grow large pearls, they are scarcer. But two pearls of different sizes may be valued the same if the smaller pearl is superior in orient to the larger. Shape determines value, too. The more symmetrical the shape, the more valuable. Pearls of irregular and asymmetrical shape are termed baroque.
Oysters grow pearls in many different shapes, from perfect spheres to long flat angel wing pearls.
Surface perfection contributes to value. The surface of a perfect pearl appears satiny smooth. But when viewed closely, natural or cultured pearls may appear to have irregular surfaces which do not detract from value, as do disfiguring blemishes. Rarity increases the value of any jewel. Cultured pearls themselves are relatively rare, as they can only be grown in limited areas of the world's oceans and take years to grow.