Pearl Information
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CHEMISTRY CaCO3 (aragonite, the outer layer) about 82 - 86%, conchiolin 10 - 14%, water 2%.
WEARABILITY* Good
ENHANCEMENTS Dying, common
*Wearability is graded as Excellent, Very Good, Good, Poor, and Forget It!
... Pearls are delicate and
CRYSTALLOGRAPHY Aragonite is orthorhombic, with crystals radially oriented.
REFRACTIVE INDEX 1.53 - 1.69
HARDNESS 2.5 - 4.5
SPECIFIC GRAVITY 2.6 - 2.78.
CLEAVAGE None
HEAT SENSITIVE Yes
SPECIAL CARE INSTRUCTIONS Avoid heat and all chemicals, including perfume and other cosmetics.
For more details see the article on "Hardness and Wearability."
...
Pearls are one of our most ancient gems with records of commercial harvesting going back 2500 years.
Their natural occurrence is very rare, with only one in several million shellfish ever producing a pearl. Oysters are the best-known source, but clams, mussels, and abalone also produce pearls.
... For a pearl to form an irritant, (usually a grain of sand,) must get deep enough inside a shell, that the animal cannot expel it. The creature's shell producing system begins coating the irritant with nacre, the shiny substance that you find on the interior of most shells.
... Nacre is composed of the mineral aragonite, with an organic binder called conchiolin. The aragonite forms minute crystals with a radial oriented, concentric structure. You can feel the edges of these crystals by rubbing a pearl against your teeth. The tooth test has long been used for pearls. Most of their imitations will feel smooth, rather than gritty, when rubbed against a tooth.
... Natural pearls almost disappeared from the market in the late 1800's due to excessive harvesting. Even today, they are extremely rare and demand a huge ransom. Necessity is the mother of invention and, as pearl sources began to dry up, several enterprising Japanese developed methods of culturing pearls in oyster farms.
need special care.
... Since they are soft, they
should be stored by them-
selves to avoid contact with
other materials.
... When getting ready to go
out, always put your pearls
on last. Do not wear them
while using aerosol hair
sprays, perfumes, etc. These
can ruin pearls.
... Clean pearls with mild
soap, (not a detergent,)
and room temperature water.
Under no circumstances
should they be placed in an
ultrasonic or steam cleaner.
Nor should you submerse
them in a chemical cleaner.
... Cultured pearl production began in Japan around 1910. Not only does the culturing process provide more pearls, it also allows larger pearls to be produced.
... The process involves inserting a mother of pearl seed, along with a piece of tissue, known as the mantel, into the oyster. After surgery, the oysters convalesce in a "hospital" for four to six weeks. They are then transferred to cages between seven and ten feet under water. Here, they are allowed to grow for three to six years.
... Freshwater pearl farms began in Lake Biwa, Japan around 1928. They have the advantages that up to thirty seeds can be inserted in a single clam and the production time is just three years. The term "Biwa" is nearly synonymous with freshwater pearls, but one should be careful about using it if the source is unknown.
... Freshwater pearl shapes were originally quite irregular, but steady improvements have been made. Today, freshwater pearls rival their saltwater cousins in shape and luster. When grading pearls, it makes no difference if they are from fresh or salt water.
... Unfortunately, pollution and illness have greatly reduced the Japanese saltwater farms in recent years. However, freshwater farming is on the rise. Freshwater pearls are being grown all around the world and the quality is constantly improving.