Unlike with other gems such as diamonds, there is no sole, universal grading system for pearls. A jeweler or seller may, however, use one or more of the systems shown here to give an idea of the quality.
GRADING SYSTEMS: the most commonly and internationally used is the AAA-A scale, (AAA, AA and A) grading system. (Sometimes + is added to one of these to make an intermediate grading such as AA+ or A+. Some sellers use AAAA or AAA+ for individual, unmatched pearls.)
Pearls of AAA are recognized as gem-quality with flawless complexion, spherical shape, and intense luster. Even a single 'A' grade pearl will have good luster, be relatively smooth and fairly free of blemishes, and have a thin to medium nacre thickness.
There is also the so-called Tahitian system, which grades on an A to D scale. This system demands a nacre thickness of greater than 0.8mm.
Both of these grading systems focus primarily on the luster and surface quality of the pearl to determine its grade.
The GIA (Gemological Institute of America) has its own scale, the GIA trademarked '7 Pearl Value Factors': Pearl Size, Shape, Color, Nacre, Luster, Surface, and Matching.
Whatever the order the standards appear in, it is generally agreed that LUSTER is the most important factor in grading.
It is LUSTER that makes the pearl unique.
It is the pearl's radiant glow that comes from light reflecting off of the many layers of nacre.
The quality of the luster is related to the THICKNESS AND QUALITY OF THE NACRE.
The thicker the nacre and the thinner and the more numerous the layers of nacre in the pearl, the finer the luster and the more durable the pearl.
The SURFACE of the pearl is also a major factor. Smoothness and blemishes are very important in grading. No real pearl is absolutely smooth, and small blemishes can be ignored when the pearl has fine nacre and luster. Blemishes are less noticeable on pearls with higher luster.
SHAPE. Spherical pearls are the rarest; symmetrical ones, tear-drop shaped, for example, are still desirable, especially when well-matched. The more irregular, baroque ones are the least expensive usually, but are perfectly acceptable when mounted or set nicely. And a perfectly round pearl is very rare indeed. Since many non-spherical freshwater pearls have fabulous luster, roundness is not given as much value. Pearls with the best luster are better than pearls with with lesser luster but more
perfect roundness.
greenish, to peacock and multi-hued. The overtones are also important. A pearl whose body color is white (more expensive and sought-after) or cream may have subtle overtones of rose or pink, for example.
SIZE matters, too. Larger cultured pearls are rarer and more expensive. In particular, Akoya pearls over 7 millimeters become much more costly. Prices rise with each millimeter. The larger South Sea and Tahitian pearls increase dramatically in price with size: 100 or 200 percent with each millimeter.
MATCHING: All of the above factors are important when matching the pearls in an item of jewelry. In a beaded strand the pearls usually graduate slowly and evenly in size, from the smallest at the back to the largest in the front. Pearls will not lay correctly if mismatched, and this reduces the aesthetics and the value of the piece.
Author : Michael Briton
Picture Credit :
http://www.pearlsofjoy.com/Pearl-Grading_ep_46-1.html
http://www.tiffany925necklace.com/graduated-south-sea-shell-multicolor-pearl-necklace-16-p-1742.html
http://www.shecypearljewelry.com/pearl-guide/pearl-quality.html
