Gemstones & Pearls:Gemology

China produces hundreds of tons of cultured freshwater pearls every year. Some categories are getting better all the time

China has made enormous strides in freshwater pearl culture in the past two decades. Once scorned as "rice krispies" because of their irregular and elongated appearance, Chinese freshwater pearls have been moving steadily toward rounder shapes, smoother surfaces and bigger sizes.

The natural-color cultured freshwater pearls shown below are a case in point. However, they are by no means abundant, requiring months or even years of collecting for a multistrand necklace, says retailer Michael Randall of Gem Reflections, San Anselmo, CA. But because of their unusual colors, lush appearance and luster, Randall has decided to carry this type of Chinese freshwater strands.

How They Form
Randall is intrigued also by how they form. They are sold as non-nucleated cultured pearls because they don't have the nucleus bead traditionally found in cultured pearls. Instead, they have a cross-section similar to that of pearls that grow naturally, with concentric layers of nacre. No study has fully documented this type of formation. However, the Summer 1994 issue of Gems & Gemology, the quarterly journal of the Gemological Institute of America, referred to them as "tissue nucleated."

"With the tremendous and still increasing production of freshwater tissue nucleated cultured pearls, and the greater attention to quality by cultured-pearl farmers in China, it is not surprising that some of these cultured pearls turn out nearly round or round," the article states.

Similarly, in her book The Pearl Book, The Definitive Buying Guide, Antoinette Matlins says: "While the exact technique used to produce these beauties is not known, we do know it involves implanting a round all-nacre nucleus perhaps made from a non-nucleated freshwater cultured pearl such as the inexpensive tissue graft rice-krispie type, shaped into round beads after harvesting and then re-implanted in another freshwater mollusk."

Characteristics
The pearls are slightly out-of-round, says Randall, but are a vast improvement over the "potato" pearls (so named because of their shape) that represented the Chinese growers' first step toward "rounding" in the early 1990s.

Today, the pearls grow as large as 10mm to 11.5mm, compared with 6.5mm to 7mm when the GIA report was published five years ago.

The pearls' natural colors include lavender, pink, orange, gold and gray, though pure white and cream are more common. The origin of the color remains a mystery. (China also produces vast quantities of pearls that are irradiated, dyed or both to achieve the same colors. See Professional Jeweler, September 1998, pp. 125-126.) You can detect dye in color concentrations on the pearl's surface (especially around the drill hole), but experts say irradiation can be very hard to detect. For this reason, a definitive determination of color origin may need to take place in an accredited gem lab.

A Chinese freshwater cultured pearl cross-section reveals concentric layers of nacre growth reminiscent of natural pearls. But the process of producing these pearls is a well-kept secret. Pearl courtesy of Gem Reflections of California, San Anselmo, CA.

A strand of 10mm to 11.5mm cultured freshwater pearls from China blends an array of natural pastel colors. Pearls courtesy of Gem Reflections of California, San Anselmo, CA.

photos by Robert Weldon

– by Robert Weldon, G.G.

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