A natural pearl is formed when a microscopic intruder or parasite enters a bivalve mollusk and settles in its shell. Reacting to this irritation, the mollusk forms a pearl sac of external mantle tissue cells and secretes the calcium carbonate and conchiolin to cover it. The secretion process is repeated many times. Natural pearls come in many shapes, the round shape being the rarest. When X-rayed, the growth rings from the layers of calcium carbonate and conchiolin deposited show up.
The large majority of saltwater cultured pearls are grown by inserting a spherical bead into the mollusk’s gonad. The trade name of the cultured pearls are Akoya, white or golden South Sea, and black Tahitian. When X-rayed, the beaded cultured pearl shows a solid center with no concentric growth rings. The majority of beadless cultured pearls are mantle-grown in freshwater shells, the trade name Chinese cultured pearls. When the beadless cultured pearls are X-rayed, it shows growth rings, but also a complex central cavity where the pearl sac formed.
Akoya pearls were originally farmed in Japan, but when the waters became very polluted Akoya farms were established in China. The sericulture process was first developed by the British biologist William Saville-Kent who passed the information along to Tatsuhei Mise and Tokichi Nishikawa from Japan. Nishikawa, who married Mikimoto’s daughter, was granted the patent in 1916. Mikimoto was able to use Nishikawa’s technology, and commercially applied the process to Akoya pearl oysters in Japan. The same technology was applied to the south sea pearl mollusk by Mitsubishi’s Baron Iwasaki.
Akoya pearls are grown in oysters that are from 6-8cm in diameter. It is rare to find a pearl larger than 10mm. Contrastingly, South Sea pearls come from mollusks that are 23 cm across, and therefore the 14mm size pearls are not uncommon.
The pearl farmers began growing cultured freshwater pearls in the early 20th century in Lake Biwa, the largest and most ancient lake in Japan. Hence, the term “Biwa” pearls. The peak production was realized in the early 1970’s when as much as six tons were produced. Due to pollution though, the Japanese producers invested in producing the freshwater pearls in the region near Shanghai, China. This area is presently the world’s largest producer of freshwater pearls.
The pearl’s value in jewelry is based upon the luster, color, size, absence of surface flaws and symmetry. Luster is the main distinguishing quality factor. But, all factors being equal the larger the pearls the more valuable it is.
Pearls come in the following basic shapes, round, semi-round, baroque, drop, pear, oval, and circled. Round shapes are the rarest and most valuable. Drop and pear shapes are used preferable in earrings and pendants. Baroques have a different appeal, sometimes a more casual style.
White and black are the most popular colors, but pink, blue, champagne, gold, green, gray and even purple saltwater pearls can be encountered. But, to collect a complete strand of the same size and shade can take years. A strand of South Sea or Tahitian pearls is usually graduated in size. A large rare pink pearl comes from the big Caribbean Sea snail, the conch.
Being an organic gemstone, pearls require special care to ensure their longevity. Simple cleaning and storage will keep the pearls lustrous for years to come.
Avoid having pearls come into contact with perfume, hairspray, cosmetics, and household cleaning agents, as they contain alcohol, acids and harsh chemicals that are harmful to the pearl’s luster and surface.
Perspiration may also harm pearls, so gently wipe pearls with a slightly damp cloth after being worn.
Pearls are strung with a knot between each pearl and if the necklace breaks, only one pearl should fall loose while the rest remain secure. The knots also keep the pearls adjacent to each other from rubbing surfaces. Silk string is preferably used to knot pearl necklaces. The string and knots can weaken and stretch over time, so pearls strand necklaces should be restrung approximately once a year. Avoid wearing pearls in water, while bathing, or swimming since the water will weaken the silk thread. Keep the pearls away from heat or other drying surroundings.
Store pearls separately from other jewelry to avoid scratching its surface. Keep pearls in a soft pouch or box. Avoid using brushes or abrasive materials on pearls since the surface would be damaged.
Lengths of Necklaces
Collar - 10 to 13 inches long, worn against the throat.
Choker - 14 to 16 inches long, hitting at the base of the neck.
Princess - 17 to 19 inches long, coming just below the collar bone.
Matinee - 20 to 24 inches long falls just above the breasts.
Opera - 28 to 35 inches long will be long enough to reach the breastbone or sternum of the wearer. The opera length necklace can be worn doubled.
Rope - 45 inches long and longer.