Richard Drucker, president of Gemworld International and publisher of the grading and pricing book The Guide, says their latest pearl grading system has been adapted to correspond with the greater variety and changing quality of pearls in the market.
Drucker has always tried to maintain consistency with GIA grading scales but worried that GIA’s latest revision of its pearl grading system would be a “one size fits all” system. Drucker felt a variation was needed for pricing. Each type of pearl, because of the way it is grown and the qualities that can be produced, should have its own quality criteria, he says. He does, however, use GIA terminology for grading and pricing.
For example, The Guide ranks Japanese akoyas equally by shape, color, luster, and blemish. The biggest change for grading akoya pearls comes in judging nacre thickness. GIA no longer talks about nacre thickness as a measurement. If nacre thickness is sufficient, no comment is made. However, if the nucleus is visible through the nacre, or if the pearl has a chalky appearance, then nacre thickness negatively affects overall quality. Drucker says that this change has come about mainly because the market produces much thinner nacre than it did years ago.
In the end, shape, color, luster, and blemish are weighted equally. A visible nucleus will give the pearl a final grade of “low good” to “middle commercial.” An obvious nucleus or chalky appearance will set the final grade at “low commercial.”
For Tahitian black pearls, blemishes and luster are combined into one category, “surface quality.” Top quality, “Quality A,” describes a pearl that shows one or a few minor defects located on less than 10% of the surface. Luster is rated as “nice” or “average.”
Weighting each quality factor would show shape and color at 25% of the overall grade, with surface quality representing 50%. Matching is not considered, says Drucker, unless it’s a poor match. Nacre thickness is not considered either, until it falls below Tahitian government standards.
For Chinese freshwater pearls, overall quality (luster and matching) is the only consideration. Shape is not considered, since there are so many. They are generally priced by overall quality and shape category. It’s important to note that excellent luster is difficult to obtain with freshwater pearls.
For South Sea pearls, The Guide adapted the Stuller & Paspaley grading system. It grades luster, shape, color, and complexion. Stuller & Paspaley was receptive to recommendations of additional elements, notes Stuart Robertson, research director at The Guide, allowing their system “to serve as a true grading standard for South Sea pearls.” Prices are based solely on quality grading, and other aspects of selling pearls, such as marketing, are not considered.