There are several determining factors to quality: luster, nacre thickness, surface, color, size, and shape.

The most important factor when measuring the quality of Tahitian pearls is the thickness of the nacre. This shows how long the beauty of Tahitian pearls will last. Those with very thick nacre will last a life time. In contrast, those with thin nacre, which will wear and lose their luster and quality with time and use.

The French Polynesia Government has set up a standard of a minimum nacre thickness of 0.8mm for Tahitian pearls. Those with less than 0.8mm nacre thickness are not allowed export.

There are four grades to rate the surface quality of Tahitian pearls: AAA, AA, A, B. AAA quality Tahitian pearls are the most valuable.

Tahitian pearls of AAA Quality are the highest in luster and have clean, smooth surface.

Tahitian pearls of AA Quality are medium to high luster, and have some slight surface imperfection.

Tahitian pearls of A Quality will have medium luster and medium surface imperfection. 

Tahitian pearls of B Quality have many slight flaws or several deep flaws over the surface of the pearl.  

The best expression of a pearl's beauty is it's quality of luster, producing light reflections from the pearl's surface. Luster measures the surface shine of the pearl.  The higher the luster, the higher the quality of the Tahitian pearl.  A nice thick nacre results in high luster. Tahitian pearls displaying the sharp, intense reflection of light are high luster and have a slightly metalic look.

There are more things to be considered in the quality and authenticity of Tahitian pearls.

For more information about Tahitian cultured pearls, please visit Tahitian pearl official web site.