Japanese Cultured Pearls

When one hears “Japanese cultured pearls,” one thinks of the name “Mikimoto” and of the traditional “akoya”—2-mm to 7-mm or even 8-mm perfectly round, high-luster, white or pink-rosé pearls. And rightly so. After all, it was Kokichi Mikimoto, a vegetable merchant and noodle salesman, who in 1919 finally perfected the technique of culturing pearls. Mikimoto grew full-round pearls by inserting beads into the pinctada martensii mollusk, now simply called akoya. But even though Mikimoto’s akoya pearls still reign supreme, Japan is known for quite a number of different cultured pearls.

History and romance. In the late 1800s, Mikimoto began implanting beads into oysters. Now the name Mikimoto is held up as the standard for excellence in high-quality akoya cultured pearls.

Natural pearls have a millennium of curious history, including references to the pearl’s being the “hidden soul of the oyster.” But even the relatively young 100-year-old cultured pearl has its own bit of folklore—for example, it’s been used for medicinal purposes to treat stomach ailments.

Most consumers know Japanese cultured pearls as the birthstone for the month of June, overshadowing alternate June birthstones alexandrite and moonstone.

Qualities. The saltwater bays and inlets of Japan contain cooler waters than most other pearl-growing countries. This cooler water temperature helps promote thinner and more compact nacreous layers, responsible for the pearl’s durability and—more importantly—its beauty. Harvesting the pearl when the waters are at their coldest creates even thinner, more compact nacreous layers, and hence the highest possible luster and durability. The purity and temperature of the waters are important, and Japan has been known for its quality pearls for almost a century. However, recent pollution and virus problems have diminished cultured pearl production.

The akoya cultured pearl is a bead-nucleated product. Just as the waters are important to the pearl’s growth, so is the bead. Starting out with high-quality mother-of-pearl beads is key to the pearl’s ultimate quality, as the roundness and nacre consistency is dependent upon the structure of the bead. Typical sizes for akoya cultured pearls range from 2 mm to 8 mm, but they can grow as large as 11 mm. Sizes also are dependent on the bead. Since it takes approximately three years to produce .5 mm of nacre, most beads are, at maximum, only .5 mm less in diameter than the measured size of the final grown pearl.

Once the bead has been implanted, anything can happen. The bead can be rejected, the mollusk can die from distress, the nacre can be discolored, or the pearl can be misshapen.

Baroque Japanese cultured pearls can offer quite an unusual look for less. Other baroque-shaped cultured pearls have no central bead. They may be freshwater mantle tissue-nucleated pearls, or—like keshi pearls—they may have no discernible nucleus.

Keshi pearls are byproducts of the culturing process. The mollusk, on its own, creates what would under normal circumstances be called a natural pearl. These pearls are typically baroque, and have more orient because of this undulating surface. Keshi and baroques are priced separately from round akoya pearls.

Other cultured pearls from Japan include the Amami golds—golden South Sea-sized pearls. Grown off the coast of the island of Amamioshima, the 8-mm to 10-mm Amami golds are larger than akoyas, the result of warmer waters that help promote thicker nacre.

Japan also produces freshwater cultured pearls. Lake Biwa pearls were nucleated with mantle tissue in the 1970s, and became popular. But in the mid-1980s, the lakeshore became overdeveloped, pollution overpowered the mollusk, and pearl production ceased. Biwa had been such an important site for freshwater cultured pearls that the Chinese would ship their freshwater cultured pearls through Japan simply to acquire the Biwa label. Today, freshwater cultured pearls come from Lake Kasumigaura. These bead-nucleated freshwater pearls are grown up to 15 mm in size and typically are naturally pink in color. Quality is high, but quantities are small.

Enhancement. Most Japanese white cultured pearls are bleached using hydrogen peroxide, reducing off-color spotting and making them more evenly white. Body colors also can be created through irradiation, and some very inexpensive items will be dyed. Overtone colors of rosé and blue also are commonly added by dyeing.

Luster is sometimes enhanced by polishing and—on rare occasions—by coating. Faceting cultured pearls can help make some off-color or blemished akoyas more salable.

Pricing. Japanese cultured akoya pearls can be priced in several different categories—for example, single pearl half-drilled for rings, pendants, and earrings; or full-drilled for use in necklaces and bracelets. Single pearls of 7.5 mm to 8 mm in fine quality range from $45 to $65 per pearl. Strands using this size in 18-in. princess lengths range from $1,500 to $3,000 per strand. Matinee lengths of 24 in. to 27 in. can range in price from $2,250 to $4,500 per strand. Commercial quality 18-in. pearl necklaces in this size should range in price from $400 to $800 per strand. Matching pearls will cost more than simply doubling the single-pearl price.

Care and cleaning. Try using a soft cleaning cloth to wipe clean your pearls. Use only a very mild detergent to wash pearls and only if absolutely necessary. Usually, it is the string that becomes dirty, and this should be replaced instead of cleaned.

The rule is that pearls go on last, after cosmetics, hairspray, and perfume. Pearls are also the first to come off and should then be wiped clean. Pearls should never be worn to the beach, as perspiration and body oils containing natural acids can damage the luster of a pearl. Don’t forget, swimming pools contain chlorine, which can “eat” a pearl.

Protect pearls from other jewelry, including other pearls. The nacreous layer is made up of tiny crystals of aragonite and calcite, which makes them potentially damaging to each other. Pearls are individually knotted on strands not only to keep them from sliding off if the strand breaks but also to protect them from rubbing against their neighboring pearls.

Bench repair and setting. Always remove the pearl before doing any type of work on a ring. Pearls are soft and easily scratched. They can also be attacked by harsh chemicals used in a workbench area.

Recommended reading. For more information, see: GIA’s Pearls Course, 1999, GIA, Carlsbad, Calif.