It also takes more time for an oyster to produce a larger pearl. Round pearls are the most valuable because of their rarity. Off round, tear-drop shape, and baroque pearls are also often quite beautiful. The depth of shine of the pearl. The thickness of the nacre determines the pearl's luster.
More luster means more value.
The amount of blemishes on the pearls surface. Cleaner pearls have fewer or no blemishes. Truly a matter of preference. Tahitian Black Pearls can range from golden to peacock to steel gray. History Pearls are the emblem of modesty, chastity and purity and they symbolize love, success and happiness.