Luster-The luster of the pearl is where you find the true beauty of a pearl and is thus its most important value factor. There are four categories of luster that are used when grading pearls.
Exellent – the reflection is distinct and sharp.
Good –Reflections are not as sharp but they are bright. The edges are a bit hazy.
Fair – Reflections are blurred, hazy and weak.
Poor – Your reflection will be dim. Luster is also different for the type of pearl. An akoya will have a very bright-mirror like luster and a South Sea parl will have a satiny soft luster