Thursday, January 19, 2012
Freshwater pearls are pearls which grow in non-saline environment in freshwater mussels. Hence the name...
China has harvested freshwater pearls since the 13th century, and is the leader in freshwater pearl production. The first record mentioning pearls in China was from 2206 BC. The United States was also a major source of natural freshwater pearls, from the discovery of the New World, through the 19th century, until over-harvesting and increasing pollution significantly reduced the number of available pearl-forming mussels in the US.
Freshwater pearls differ from other cultured pearls, in that the great majority of them are not bead-nucleated. Freshwater mollusks are nucleated by creating a small incision in the fleshy mantle tissue of a 6 to 12 month old mussel, then inserting a 3mm square piece of mantle tissue from a donor mussel. Upon insertion, the donor, (graft) tissue is twisted slightly, rounding out the edges. What happens after this point is really just speculation. Some believe that this tissue acts as a catalyst in producing a pearl sac thus making the 'nucleation' actual 'activation'. Others believe the tissue molds with the host to create a pearl sac, while still others maintain the tissue is the actual nucleus. Although it is said that a freshwater mollusk can withstand up to 25 insertions per valve, it is common industry practice to perform only 12-16 insertions in either valve, for a total production of 24-32 pearls. The mollusks are then returned to their freshwater environment where they are tended for 2-6 years. The resulting pearls are of solid nacre, but without a bead nucleus to guide the growth process the pearls are rarely perfectly round.
From George Frederick Kunz's, 1908 masterpiece, 'The Book of the Pearl'
The Chinese freshwater pearls come in a wide color range that includes white, champagne, cream, orange, pink, purple, lilac, mauve, blue and brown.
Bleaching, dying, and polishing do occur. Except for the old Arabic practice of sun-bleaching in the Persian Gulf, naturals were practically never processed. Chinese pearls that are nearly white or mottled are usually bleached to make them whiter and more uniform. With the same methods perfected by the Japanese, the Chinese use a mild bleach, bright fluorescent lights, and heat. They polish surfaces by tumbling pearls in pumice or similar substances. The idea, as always, is to facilitate matching pearls for strands.
Fire Mountain Gems has many shapes of Cultured Freshwater Pearls. I did not know there were so many!