Almost all pearls in the contemporary jewelry marketplace are cultured, including those from the primary ocean and freshwater lake sources in Japan, freshwater pearls from China, Tahitian pearls, South Sea pearls from Australia, Indonesia, the Philippines and Myanmar and from the great State of Tennessee. The cost and value of all pearls is determined by size and quality.
Size and Length:
Pearls are weighed in Japan; the measure of their weight is the momme, and old unit of weight in both China and Japan, and in use today only in Japan. One momme equals 3.65 grams or 18.75 carats. However in most of the world, pearls are sold by their millimeter diameter. Cost increases as millimeter size increases. Japanese akoya cultured pearl necklaces, the most commonly seen and purchased in the 20th century, begin at about 2.5mm to 3mm and reach 11mm or a bit more. Necklaces presented to young women in high school are usually between 5.5mm and 6.5mm; those presented to college graduates reach 7.5mm. A pearl necklace measuring between 7mm and 8mm represents the classic jewel in an 18 inch length, and it has served as the standard bearer of a woman’s pearl collection, worn continuously decade after decade.
As stated elsewhere, pearls on a necklace should vary by no more than one half millimeter; therefore a necklace may contain pearls that range from 7.5 mm to 8mm, as long as both sizes are represented on the strand. If the pearls vary by more than one half millimeter, the cost drops. An exception would be a necklace of purposefully graduated cultured pearls, often provided as wedding gifts decades ago. Graduated necklaces are beautiful and come in and go out of fashion over the years.
Judging pearl quality is complicated and requires years of patient and continuous practice. Quality features apply to a single pearl, pearls on a necklace as well as pearls in all kinds of jewelry.
Nacre:
A small organic bead is inserted into the mollusk, which then secretes layers of nacre around it, to protect its delicate tissues. The longer the bead is left in the mollusk, the more nacre is secreted. When the shell is opened, hopefully a pearl is waiting. The longer the growing period, the thicker the nacre and the finer the pearl. Discussing with your jeweler the thickness of nacre surrounding the pearls in your necklace is extremely important….essential for high luster that will remain for generations and important to the cost of the strand. The better necklaces show from .5mm to 1mm plus of nacre. Nacre thickness is almost impossible to measure, and can only be determined accurately by x-ray. However, experienced pearl buyers can see the result of longer growth periods, by visual examination of the luster.
Most pearl farmers are anxious to get their pearls to market and therefore allow only a short period of growth, and this produces lower and commercial quality pearls, which make up the majority of pearl jewelry in the world market. Luster is defined as the glow or sheen, which is caused by light circulating through layers of nacre. When the pearl has heavy nacre, luster is rich and bright.
Even pearls that have minimal nacre are polished before they are strung onto necklaces. The polished pearl surface produces reflected light, and this is often misidentified as luster. So even inexpensive necklaces, when new, can be fairly bright. Still, if you compare a pearl necklace with thick nacre and good polish to a necklace with light to medium nacre and good polish, the difference is easy to see. The other problem with light nacre is that the minimal layers have a tendency to wear off with the use of cosmetics, resulting in the appearance of the center nucleus. Also, such pearls may actually change color over time, sometimes developing a yellowish body color with minimum luster. None of these problems can be repaired. They may be prevented or at least postponed by careful cleaning every time pearls are worn, and by allowing perfume, hair spray and various creams to thoroughly dry before donning pearl jewelry.
Shape:
Pearls are cultured in many shapes, by inserting nuclei of many shapes. For the classic necklace of akoya pearls, the best shape is round. As pearls become slightly out-of-round and then finally completely misshapen, call baroque, the cost drops. Necklaces of misshapen pearls can provide fun fashion, and should be inexpensive. Generally speaking, there are 3 shape categories for this gem:
• round,
• symmetrical and
• baroque,
and these can be further sub-divided …
Example: symmetrical pearls include oval, button and drop. These are not considered baroque pearls; rather, they are considered fancy shapes, analogous to fancy shape diamonds. Pearls from different parts of the world are classified by different shapes.
Example: the Tahitian dark pearls. There are 5 shapes of Tahitian cultured pearls. They are round, drop, button, baroque and circled. Each can be beautiful, and each carries a different cost.
The most diverse selection of shapes comes from the huge annual production of Chinese freshwater pearls, and almost all of these are inexpensive and sometimes very fun fashion. China also continues to experiment with the akoya mollusk, in hopes of producing pearls as round and with the beautiful luster mastered by the Japanese over the decades of the 20th century. As of 2009, this research has not been completed.
Body and Overtone Color (Iridescence):
Body color is the color everyone sees, and gemologists define it similarly to color in colored gemstones: the hue, the intensity (lightness to darkness) and saturation (its purity). For Japanese akoya pearls, there are 3 primary body colors:
• rose
• white
• cream
Overtone color is iridescence, which is one of the light phenomena in the gem kingdom. An iridescent pearl appears to have a secondary color(s) floating in a circle across the top of the pearl. For Japanese pearls, iridescent colors are pink, blue and green. These pearls can have one, two or three overtone colors. The rarest and highest quality would be a combination of pink and blue overtone, creating a slightly purplish light effect across the surface of a white pearl.
Cultured pearls from Lake Biwa Japan exhibit many fancy colors, all part of growth. In the 1990’s, strong pink and orange pearls from Lake Kasumingaura reached western markets under the name Kasumiga Pearls. These pearls were seldom round and exhibited wrinkles and knots along their surfaces. Black, brownish-black and reddish black pearls from Japan are dyed, and we now know that most of the dark Tahitian cultured pearls are treated to deepen their color. Certain mussels used to culture freshwater pearls in China produce intense purple, mauve, orange and pink pearls in addition to white. These colored pearls may be stabilized by a bleaching process before they are sorted and strung into necklaces.
Bleaching, Dyeing, and Coating:
Like most colored gemstones, most pearls are enhanced in some fashion after they are removed from the mollusk. The question of what kinds of treatments are okay and what kind are deceptive continues to be debated within the industry. As with diamonds and colored gemstones, I feel that all treatments to improve the quality of a pearl should be disclosed to the buyer. Most pearls are bleached and then polished. Bleaching is known to create a uniform color. After bleaching, most Japanese akoya pearls are then colored to produce a light pink overtone. Such pearls are not considered dyed, and the pearl industry has accepted this process for decades, without the need to disclose it to the buyer. Dark pearls from Japan are created by immersing them in a silver nitrate solution. Certain large pearls from Tahiti showing a dark color are also treated in this fashion. Blue, green, purple and brown aniline dyes are also used to dye cultured pearls. Gemologists can sometimes test these pearls for dye by using ultraviolet fluorescence and or by microscopic examination of the drill hole, and there are additional tests available at advanced gemological laboratories using expensive equipment. A difficult challenge is determining the origin of golden color in South Sea cultured pearls. Chemically dyed pearls are substantially less expensive than natural golden South Seas which have become difficult to find in recent years. The GIA is currently researching a reliable testing method for these pearls, even though the pearl industry admits that the great majority of golden pearls are dyed in some fashion. Finally, some akoya cultured pearls and some white and black South Sea and Tahitian pearls are coated with a type of silicon polymer film to improve luster. There are several methods of testing for this type of enhancement.
Surface:
Few pearls have unblemished surfaces. Gemologists consider the size, distribution, type and visibility of surface markings. Like imperfections in diamonds and inclusions in colored gemstones, pearls grow with many kinds of surface marks. These include bumps, knots, grooves, pits, dull spots, scaly spots, growth rings and many more. If the surface markings are immediately visible, the pearl is downgraded and much less expensive. If the beads must be examined closely to see blemishes, we would call these ‘slight growth characteristics’, and they would not de-grade the value of the necklace very much. Many Chinese freshwater pearls show wrinkling on their surfaces. They are often compared to raisins or prunes.
Matching:
Analyzing the cost and value of pearl necklaces includes observing how all the beads match in millimeter diameter, nacre thickness, luster, shape, body color, overtone color and surface features. The better pearl necklaces contain pearls which match closely in all features. If a couple of pearls are out-of-round and the balance are round, the necklace is downgraded only a little, assuming all other features are well matched. As more beads vary from the ideal, in any of the features, the cost continues to drop. No more than 25% of the value of a necklace should be attributed to the matching of its features.
