Cultured Pearls

Definition

A pearl produced with or without the insertion by man of a bead by grafting, followed by maintaining the mollusk in cultured until the pearl is harvested. Cultured pearls are nacreous, unattached formations, secreted in the interior of pearl oysters including Pinctada maxima, Pinctada margarifigera, Pinctada mazatlanica, Pinctada funcata, Pteria penguin, and Pteria stema as well as the freshwater mussels Cristeria plicata, Hyriopsis schlegeli and Hyriopisis cumingii. The surfaces of cultured pearls are composed of nacre, laid down in concentric layers while within the pearl sack. The secretion of the nacreous layers from the mantle of the pearl oyster is natural process instigated and partially controlled by man. This applies to all cultured pearls whether grown with or without a bead. The term cultured applied to pearls that have been cultured is not applied to other pearls.

Current and Historic

There is now an enormous market in cultured fresh and saltwater pearls. The insertion of objects such as figures of Buddha between the shell and mantle of mollusks, in order to obtain a covering of nacre, has been practiced by the Chinese since the thirteenth century.

The Chinese are considered today as the inventors of the cultured pearl. Regular production started as early as the 12th century, while first evidence dates back to the 1st century BC. China’s present cultured pearl industry started only about 40years ago. Classical Japanese literature makes allegoric references to pearls, this could lead to the conclusion that freshwater pearls were known quite early on as well. It appears as if natural pearls have never been particularly significant but Japan rose to fame with the development of its cultured pearl industry in the 20th century.

Types of cultured pearl

There are four important commercial cultured pearl in market: Freshwater cultured pearls, Akoya cultured pearls, South Sea cultured pearls and Tahitian cultured pearls.

Nucleated Cultured Pearls

A pearl produced with a bead by man, then is maintained in culture mollusk until the pearl is harvested.

The Culturing Process

The modern production of cultured round pearls is highly organized on large pearl farms where the oysters are reared. When the oysters are three years old, they are ready for the culturing process and are lifted out of the water. Each will receive an implant of one or more spherical mother-of pearl beads, usually obtained from a North American freshwater mussel. An oyster is killed and the mantle cut into small pieces. Each piece is put in contact with a mother-of-pearl bead nucleus and placed in an incision in the body of the host animal.

Up to 20 beads of 2-3mm may be inserted in a single animal, but only one bead of about 6mm beads up to 12mm diameter may be used, depending on the variety of bivalve. Up to 50% of the oysters will die or reject these implants.

The incisions usually begin to heal within five to seven days and the epithelium cells of the implanted square of tissue start to divide and join into an epithelium or pearl sack.

The Shape of Cultured Pearls

The shape of the pearls depends on the shape of the pearl sack, which by itself is not really round. The rounded shapes had become possible due to improvements in technology and because the sankaku mussel was used again. The mussel tends to produce symmetrical shapes with smooth surface as a result of prolonged growth periods, while the karasu mussel is inclined to produce irregular baroque shapes.

The fact that China has produced perfectly round freshwater cultured pearls without a mother-of-pearl nucleus, even in sizes of up to 15mm, for some years now leads to the conclusion that the Chinese have found a way to influence the shape of the pearl sack.

Non-nucleated cultured pearls

It is a term used in the trade for a non-beaded and keshi cultured pearls.

Non-beaded cultured pearl means a cultured pearl grown without a bead.

Cultured pearls which didn’t require the insertion of a bead nucleus were first produced in Lake Biwa in Japan. The mollusk used was a freshwater mussel which is native to the lake and produced pearls up to about 7.5mm diameter. In recent years, pollution has stopped production in Lake Biwa. During the same period, however, there has been rapid and huge growth of the non-nucleated cultured freshwater pearl industry in China. Better quality Chinese pearls are similar in appearance to those from Lake Biwa and produced in the same way, using the mussel variety Cristaria plicata.