Pearls from Bobbie       

A pearl is created by a mollusk when an irritant causes it to secrete alternating layers of material, called  "conchiolin" and  "nacre", to coat the invader and make its presence less bothersome.  This irritant forms  the  nucleus  of the pearl. With natural pearls, this irritant is probably a parasite or a piece of debris   that the animal is unable to wash away. Nearly all pearls on the market are "cultured" pearls, a small piece  of tissue from a fresh water mussel is inserted into another mussel to stimulate pearl formation .
            
Pearls are classified by Origin, then graded by size, shape, nacre thickness, color, luster,surface clarity and matching. These qualities are not considered equal. Some factors will be weighted to give them more influence in arriving at a final grade. A very thin nacre thickness, can be expected for a similar quality Akoya pearl.

Grading Pearls

Grading is relative to the best attainable quality for the type. For example, South Sea pearls, which grow in 
warmer water for longer periods of time, generally have a lower luster and more tiny blemishes than Japanese Akoya pearls, that grow in colder water and  for shorter periods of time. South Sea pearls are graded against  each other.

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