Luster is the amount of light a pearl reflects from both its surface glow and the deep, mirror-like reflection of its inner light. The better the nacre quality of the pearl, the more superior its luster. Less luster means that the pearl was harvested too early and not enough nacre was developed.
Shape
Of the many shapes available, perfectly round pearls are the rarest and most valuable.
Flaws
Subtle blemishes and tiny marks are part of a pearl’s natural texture and proof of its genuine origin. Fewer surface imperfections denote a higher quality more valuable pearl.