Pearl is the only gemstone to come from a living creature and not from under the earth’s surface. Pearls require no cutting or polishing like gemstones do. Almost any shelled mollusk can, by natural processes, produce some kind of “pearl” when an irritating microscopic object becomes trapped within its mantle folds, but the great majority of these “pearls” are not valued as gemstones.
Long known as the “Queen of Gems,” pearls possess a history and allure far beyond what today’s wearer may recognize. Throughout much of recorded history, a natural pearl necklace comprised of matched spheres was a treasure of almost incomparable value, in fact the most expensive jewelry in the world. Now we see pearls almost as accessories, relatively inexpensive decorations to accompany more costly gemstones.
Gem quality pearls are very rare in nature and come from certain types of clams. Many hundreds of pearl oysters or mussels must be gathered and opened, and thus killed, to find even one wild pearl; for many centuries, this was the only way pearls were obtained, and why pearls fetched such extraordinary prices in the past. Cultured pearls are formed in pearl farms, using human intervention as well as natural processes.
Natural pearls are nearly 100% calcium carbonate and conchiolin. It is thought that natural pearls form under a set of accidental conditions when a microscopic intruder or parasite enters a bivalve mollusk and settles inside the shell. The mollusk, irritated by the intruder, forms a pearl sac of external mantle tissue cells and secretes the calcium carbonate and conchiolin to cover the irritant. This secretion process is repeated many times, thus producing a pearl. Natural pearls come in many shapes, with perfectly round ones being comparatively rare.
Cultured pearls are the response of the shell to a tissue implant. A tiny piece of mantle tissue (called a graft) from a donor shell is transplanted into a recipient shell, causing a pearl sac to form into which the tissue precipitates calcium carbonate. There are a number of methods for producing cultured pearls: using freshwater or seawater shells, transplanting the graft into the mantle or into the gonad, and adding a spherical bead as a nucleus. Most saltwater cultured pearls are grown with beads. Trade names of cultured pearls are Akoya, white or golden South sea, and black Tahitian. Most beadless cultured pearls are mantle-grown in freshwater shells in China, and are known as freshwater cultured pearls.
Cultured pearls can be distinguished from natural pearls by X-ray examination. Nucleated cultured pearls are often ‘preformed’ as they tend to follow the shape of the implanted shell bead nucleus. After a bead is inserted into the oyster, it secretes a few layers of nacre around the bead; the resulting cultured pearl can then be harvested in as few as six months.
When a cultured pearl with a bead nucleus is X-rayed, it reveals a different structure to that of a natural pearl (see diagram). A beaded cultured pearl shows a solid center with no concentric growth rings, whereas a natural pearl shows a series of concentric growth rings. A beadless cultured pearl (whether of freshwater or saltwater origin) may show growth rings, but also a complex central cavity, witness of the first precipitation of the young pearl sac.
Fine quality natural pearls are very rare jewels. Their values are determined similarly to those of other precious gems, according to size, shape, color, quality of surface, orient and luster.
Single natural pearls are often sold as collectors’ items, or set as centerpieces in unique jewelry. Very few matched strands of natural pearls exist, and those that do often sell for hundreds of thousands of dollars. In 1917, jeweler Pierre Cartier purchased the Fifth Avenue mansion that is now the New York Cartier store in exchange for a matched double strand of natural pearls Cartier had been collecting for years; at the time, it was valued at $1 million USD.
Besides being soft, pearls are easily damaged by chemicals like perfume, vinegar and lemon juice. Heat can turn pearls brown or dry them out and make them crack. Dry air can also damage pearls. When taking off a pearl ring, grasp the shank, or metal part, rather than the pearl. This will prevent the pearl from loosening and coming into contact with skin oil on your hand.
For cleaning special care should be taken. Only use jewelry cleaners labeled as safe for pearls. Never use an ultrasonic cleaner. Never steam-clean pearls. Never use (or expose pearls) to dish or wash detergents, bleaches, powdered cleansers, baking soda, or ammonia-based cleaners (like Windex). Never use toothbrushes, scouring pads or abrasive materials to clean pearls. Take your pearls off when applying cosmetics, hair spray, and perfume, or when showering or swimming.
Pearls symbolize love, purity, chastity, romance and eternity. Pearls are a favorite gem for wedding jewelry. It has been a favorite for people of many cultures. An old Arab legend tells that pearls were created when dew drops filled with moonlight fell into the ocean and were swallowed by oysters. Freshwater cultured pearls are a beautiful inexpensive gift for any June birthdays.