While an international grading system does not exist for pearls, each producer, wholesaler and retailer sets their own standards. Most use the traditional A (lowest) through AAA (highest) grading scale.
The industry does recognize seven different factors to assign value: nacre quality, luster, size, shape, color, surface, and matching.
NACRE: Nacre is the outer coating of material that makes a pearl look like a pearl. The quality of nacre involves how thick and dense it is. Thickness is contingent on how long the mollusk is in water before it is harvested. Minimum thickness is 0.4 millimeters and anything less will eventually peel. Pearls that are harvested in the coldest season of the year deposit nacre at a slower rate because mollusks’ metabolism slows. The result is a dense, compact nacre and higher luster.
Mollusks are left in water for at least ten months, although at this stage the nacre is thin with lower than average luster. Most mollusks are in water for 18 or 24 months.
LUSTER: Luster is the most important value factor, which is determined by the amount and the quality of light reflected from the surface and just under the surface of a pearl. Fine luster is a sharp, shiny reflective surface, whereas low luster is dull or chalky reflections. The finest luster exhibits a prismatic effect, due to light passing through layers of nacre and reflecting back through the surface - also known as “orient”.
SIZE: The larger the pearl, the greater the value when all other factors are equal.
SHAPE: Most mollusks are nucleated with a perfectly round bead implant, resulting in round (the most prized) or nearly round pearls. Often, other shapes like drop, oval and baroque occur and can be quite valuable - especially baroque pearls. Baroque pearls are fancy shapes that are asymmetrical and free-form.
COLOR: The color of pearl is dictated by the lip color of the pearl, as well as the species of mollusk tissue that is grafted around a nucleus. Pearl color is comprised of two components: body color and overtone. Body color is the primary color caused by pigment versus light interference. Overtone is the secondary color that appears due to nacre layers interfering with light and splitting the components.
SURFACE: Just like our fingerprints, the surface of each pearl is unique to their individual growth characteristics. Bumps, dimples, scratches, dull patches and spots which may be present on the surface of a pearl are known as “blemishes”. The fewer blemishes (when all other factors are equal), the more valuable the pearl is.
MATCHING: Because no two pearls are identical, a lot of time can be involved in composing a matching pair of pearls in terms of of size, quality, color and shape. Even more so with a finely matched single strand of pearls. It requires time and a skilled technician to sort through thousands of pearls to identify the closest match. For the rarest of pearls, this could take years!
Pearls are cultured around the world where the water’s ecosystem is pristine, healthy, and rich in various forms of plankton and nutrients for mollusks to thrive. As filter feeders, they absorb any impurities in the water, so this affects the health of the mollusk and therefore the quality of pearl.
Different species inhabit different regions and produce a diverse array of pearls. Below is a list of a few.
FRENCH POLYNESIA = BLACK TAHITIAN PEARLS: Interestingly, these pearls are rarely black! Instead, they exhibit an array of body colors and rainbow overtones with a play of color caused by the pearl’s iridescence. The most highly valued exhibit peacock overtones with a stationary, colorful shimmer as the pearl is turned. Black Tahitian pearls are not necessarily from Tahiti, but from the greater expanse of French Polynesia and Cook Islands.
AUSTRALIA = SOUTH SEA PEARLS: Pearls farmed south of Japan are considered “South Sea” pearls. They are large, luminous, and silver-white pearl that are considered the Rolls Royce of cultured pearls - and among the world’s most prized.
NOTE: Pearls grown on Palawan in the Philippines and in various parts of Indonesia also qualify as South Sea pearls.
PHILIPPINES = GOLDEN SOUTH SEA PEARLS: Rare, large and extraordinarily valuable. The rarest of the rare are those that display a deep 22 karat golden body colors. These most sought after pearls are grown in the few locations were tropical waters are more mild (around 80°F - 88°F). Fewer hatcheries do also exist in Indonesia and Australia.
JAPAN = AKOYA PEARLS: White, round and lustrous, these classics have been revered for more than 100 years. The finest emit a glow rarely found in other cultured pearl varieties. It was this pearl that Mikimoto began to culture with his 1916 patent, enabling more people to enjoy these luminous treasures.
CHINA = FRESHWATER: China is a market leader in the freshwater pearl industry. Two distinctive variations of freshwater pearl are the traditional (non-beaded) freshwater pearls and “new” nucleated freshwater pearls. The biggest difference is the former (grown with a tissue graft) rarely grows larger than 10 millimeters and the latter (grown with a nucleus) are “small” at 12 millimeters and can reach more than 20 millimeters in diameter and 40 millimeters in length! New freshwater pearls are produced in every natural color and an infinite number of innovative shapes, such as the “fireball pearls” and “cultured soufflé pearls”.
KESHI PEARLS: Though “keshi” is Japanese for “poppy seed”, this pearl refers to luminous little “accidents” that can occur in any cultured mollusk around the world. They may be the result of a dislodged nucleus, with the remaining tissue graft becoming a pearl - or - some other natural occurrence, the way that natural pearls form in the wild. While they do not have a nucleus, they are not considered “natural” due to human intervention. Very often they are small and have a freeform shape - similar to baroque pearls.
Nearly all cultured pearls in the market have been treated after harvest - to varying degrees. Bleaching is one treatment that is a standard, accepted practice to achieve a white color. Though it is not necessary to disclose bleaching, other treatments that alter the pearl’s appearance should be noted.
Such treatments are: irradiation, heating, dying, filling, and waxing.
One treatment that is not acceptable is “coating,” to enhance luster. Think of it as a coat of clear nail polish, which may eventually chip or peel, revealing the low-luster pearl below it.
Knowledge is power and any of the above treatment impacts market value.