How Are Pearls Graded?

Neither natural pearls nor cultured pearls have a grading system that the whole trade shares, and that shapes how any pearl grade should be read.

Why pearls have no universal grade#

Many in the trade have called for a pearl grading system like the one used for diamonds. CIBJO says that is extremely difficult, because pearl quality factors are more complex and delicate than those of any other gem, personal tastes in shape and color come into it, and necklaces add the matching of many pearls.¹

Various businesses and organizations have created grading systems based on their own standards. CIBJO says these have often contradicted one another and confused the market more than they ordered it.¹

How a laboratory grades pearls#

GIA’s laboratory describes pearls using its 7 Pearl Value Factors: size, shape, color, nacre, luster, surface and matching.² Its gemologists judge color, luster, surface and matching under controlled lighting against sets of master pearls, and a second gemologist repeats the observations independently.² A GIA report also records whether the pearls are natural or cultured, the water they grew in, the mollusk when it can be determined, and any detectable treatments.³

How governments have graded pearls#

Japan. Japan’s only quality inspection of pearls was once a government inspection of pearls for export. Pearls were rated on nacre thickness, shape, luster, blemishes, flaws and finish, then given a final grade from 1 to 5, and only the top three grades passed as “H” for export.¹

French Polynesia. Under the territory’s pearl law, every Tahitian cultured pearl is classified by general criteria, its size, weight, shape and surface quality, and by additional criteria such as color, assortment, pairing and nacre thickness.⁴

Reading a seller’s grade#

A grade quoted by a seller may come from the seller’s own scale, so ask which system it uses and what it measures. The page AAA pearl grades explains letter grades. For valuable pearls, a laboratory report states what the pearls are as well as their quality. The quality section explains each value factor.