||A brief history of pearls
QUALITY FACTOR ONE: LUSTER
When experts evaluate pearls, luster is the most important quality. It refers to two things: its brilliance, which is the way its surface reflects light, and its inner glow, which is the way it refracts light.
The Pearl Luster Scale
Typically, experts evaluate a pearl's luster on a scale that ranges between high and low.
Pearls with a high luster are bright and have a deep glow. High-luster pearls can reflect nearby objects clearly, and most - but not all - have a thick nacre coating. However, thick nacre doesn't guarantee a high-luster pearl; that's because some oysters have genetic imperfections that don't allow them to secrete nacre in perfect patterns.
Pearls with low luster may appear dull, chalky or too white. Usually, pearls with low luster have thin nacre.
Dividing pearls by quality factors, including luster, is not an easy task. In fact, pearls are first sorted into broad categories to make the sorting process easier. Each time a pearl goes through the sorting process, it is further classified until it is properly classified.