There Is No Industry-Wide Standard Pearl Grading System - Yet
As with any other item that can appear in a wide variety of shapes, sizes, colors and conditions, a standardized system of grading must be used when purchasing or selling pearls. Only in this way can the pearl be described according to mutually agreed-upon and understood terms, so that both buyer and seller can determine a fair price. Unfortunately, the pearl industry as a whole has not adopted a universally used standard grading system. Instead, the specific grading system often used, depends upon the specific jeweler or pearl distributor. Eventually a standard system will come into the market - most likely developed by the Gemological Institute of America. Until that time, those in the industry must rely on commonly accepted grading systems derived from the quality grading characteristics of pearls.
There Are Two Major Pearl Grading Systems – But Buyer Beware
Two major grading systems are in fairly widespread use: the AAA-A system and the A-D system (also called the Tahitian system). These are the most accepted systems, and considered standard by nearly all reputable pearl dealers, both retail and wholesale. But even these systems can become misleading if a seller uses terms from the grading system, (such as "AAA") but uses them to describe a different quality pearl than that which the system is generally understood to be describing. Or a seller could use a term not in the grading system (such as "AAAA") to make it appear that the pearl is beyond even the highest standard quality -- when in reality, that seller's "AAAA" pearls are actually equivalent to the more-common "AAA" grade, and his "AAA" pearls might only be equivalent to the commonly used "AA." Use of "AAAA" or "AAA+" is considered bad taste, or even dishonest, by most reputable pearl dealers. It is seen as a way to simply charge the customer more without providing a superior product.
Intermediate Grades And Pearl Grading For Stands
Some reputable sellers may also use intermediate grades for the pearls - those pearls that do not fall in a category but are between two - such as A+ and AA+. Obviously, these grading categories are quite broad and leave room for interpretation and individual judgment. Also note that in multi-pearl pieces such as strands, necklaces, bracelets, etc., every one of the individual pearls may not absolutely meet the indicated grade level. For example, a strand referred to as "AAA" must have most of its pearls as AAA pearls. However, a few pearls could have slightly lower luster or a tiny bit more surface defects. This is because matching is also a primary consideration in multi-pearl jewelry, sometimes even overriding a very strict grading of each individual pearl.
The A-D System (or Tahitian System)
It is important to note that the following grading system can be interchanged with the AAA-A system. For more information please refer to: South Sea Pearl Grading
This system grades pearls on a scale from A to D, with A being the highest grade. This is the system used in French Polynesia (based on a government standard there) to grade Tahitian pearls, and South Sea pearls only. It is therefore sometimes referred to as the "Tahitian system." While this system is standard in producing countries, other markets will still utilize AAA-A.
Nacre Is The Final Factor In Grading Pearls
Both of the grading systems described above focus primarily on the luster and surface quality of the pearl to determine its grade. But keep in mind that other factors also contribute to the quality and final grade of any pearl. One of the most important is the thickness of the nacre, which often determines how durable the pearl will be over time. The thicker the nacre, the stronger and longer-lasting the pearl (provided it is treated well, of course!) For Tahitian pearls, the government of French Polynesia has set a minimum nacre thickness of 0.8 millimeters. Any pearls with nacre of less than that thickness are not allowed to be sold. Keeping in mind that Tahitian pearls tend to be larger than many other pearls (such as akoyas), you can use this rule as a guideline when evaluating your own potential pearl purchases.