Pearl Color
An inportant value factor to consider when grading pearls is the color - both overtone and body color.
Pearls come in a wide variety of colors, ranging from white all the way to black. Here again (as with many of the characteristics of pearls), the fact that the pearl is an organic gemstone, formed within a living creature, contributes to the myriad unique ways in which its coloration can develop.
The natural color of a pearl results from a combination of several factors:
- The pearl's bodycolor is its main color. This can be white, silver, cream-colored, gold, green, blue, or even black. The bodycolor is determined by the type of oyster or mollusk that produces the pearl (certain types of oysters generally produce pearls of certain colors), as well as the conditions of the water, and sometimes the type of nucleus which is implanted to stimulate the pearl's creation.
- Overtones are translucent colors which sometimes appear over top of the pearl's main bodycolor. These overtones tend to alter the bodycolor somewhat, as well as adding depth and glow. A pearl may be white with rose overtones, for example. Some pearls have no overtones at all.
- The term orient refers to the shimmering, iridescent colors which appear to move and glitter when the pearl is turned. This phenomenon is caused by the way in which light is reflected through the various thin layers of nacre which make up the pearl.
It is important to note that many pearls are artificially colored. This is widely practiced with freshwater, akoya, and at times Tahitian pearls. The colors are artificially infused by a treatment knows as dying, or by subjecting the pearls to irradiation. These treated colors are typically easy to spot by a trained observer who may peer down the drill hole looking for concentrations of color which indicates the persence of dye, or a darkened pearl nucleus which indicates radiation treatment.
One rule of thumb in spottings treated pearls is that if the pearls are not true Tahitian pearls, from the Black Lip Oyster (Pinctada margaritifera), they cannot naturally be black. Naturally black akoya and freshwater pearls do not exist, and if black pearls of this variety are offered for sale, they will always be dyed. Many unwary consumers consumer buys black pearls-only to find later that the natural color grading is false.
In the 1930s, freshwater pearls from Japan's Lake Biwa introduced a wide variety of new colors to the pearl market -- colors which were previously unavailable in saltwater pearls. Today, Chinese freshwater pearl farmers have continued this trend with many fancy colored pearls harvested in large numbers.
From Pearl-guide.
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