Fresh Water Pearls
are unique among gemstones, being the only ones found within a
living creature and the only ones that requires no fashioning,
(cutting or polishing,) before use. Another distinctive feature is
its near exclusive use by one gender. Although some efforts have
been made to market pearl jewelry to males in recent years, pearls
remain the most "feminine" of all gemstones. Designated officially
as the June Birthstone, it is, unofficially, a near requirement for
... Cultured pearls are those that form
in certain mollusks, (oysters and mussels,) at the intervention of
man. A piece of mantle tissue, or a shell bead, is inserted into the
interior of the animal. This causes it to secrete a layer of organic
material, (conchiolin,) over the irritant, followed by layers of
nacre (nay-ker.) The composition and structure of this nacre is
essentially identical to that which forms under natural conditions.
The thin layers of nacre create a kind of diffraction grating
through which light must pass and are responsible for the surface
iridescence, called orient, so admired in pearls. Pearls have both a
body color and "overtones" of rainbow hues created by the orient.
The culturing process takes place over a period of one to three
years, depending on the conditions, the species and the desired
... The commercial process for raising
freshwater pearls originated in Lake Biwa, Japan at the end of the
1920's. Various problems, such as pollution and viral diseases, have
hampered production in recent years. Progress is being made in
restoring the ecosystems and breeding resistant mollusks, so we
should see a return of Japanese pearls to a prominent place in the
market in the future. At present, however, the premier source is
... Although once thought of as an
inferior product, advances in technique and marketing practices have
made today's Chinese freshwater pearl a true gem. The US continues
to command a share of the market with the pearls produced from areas
in the South, especially the Tennessee River. Culturing pearls is a
delicate process, not assured of success - only 25 - 50% of the
altered mollusks produce pearls and generally, only a small
percentage of the pearls harvested are of gem quality.
... The natural range of colors in
freshwater pearls is from white to tan to gray, depending primarily
on the species that is used in production. Enhancements are so
common that unless it is specifically stated by the seller, you
should assume a pearl has been at least bleached to remove dark
spots of conchiolin that show through the nacre. More dramatic
techniques, such as dying or irradiation, produce pearls with exotic
colors such as green, rose and lavender.
... Pearls are generally named by
their shape; so we have baroques that can be any shape, stick
pearls, button pearls, seed or rice pearls, rounds and drops. There
are blister pearls, which are created by attaching a bead or other
nucleus to the shell of the mollusk and then cutting it out after it
has become nacreous. Mabe pearls are assembled from blister pearls,
which are filled and glued to a shell base. The term "Keshi" has
come to be used for just about any baroque pearl, but in its
strictest sense refers to a pearl that spontaneously forms in the
oyster during the culturing process, without mantle tissue or bead.
... Although pearls are delicate, they
have been successfully used in jewelry for thousands of years. As
they are sensitive to heat, chemicals and abrasion, they should be
stored in a cloth bag or their own box away from contact with other
materials. They should be protected from chemicals such as hairspray
and perfume. Wiping them with a damp cloth after wearing and
occasional cleaning in mild soapy water is all that's required.
Under no circumstances should they be placed in an ultrasonic or
steam cleaner. Jewelry settings in rings and bracelets should be
protective, or if not, (as in many pearl rings,) the piece should be
considered for occasional use only, rather than daily wear.
... Faux pearls have been around for a
long time and can consist of a variety of materials such as glass,
plastic or shell with various surface treatments meant to simulate
the pearls luster. With cultured pearl prices at historic lows,
there is little incentive to buy or wear imitations. A rule of thumb
when testing a suspect pearl is to rub it across the surface of your
teeth. Real pearls will feel slightly gritty, most imitatons will
... The value of a pearl is most related to the thickness and
quality of the nacre. Other factors include size, (especially in
rounds) shape, and color. In general, the highest prices will be
paid for large, round, well colored, unenhanced gems. Factors that
influence value in pearl jewelry pieces would add to these general
considerations, quality of stringing and degree of matching in size
Salt Water Pearls
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.
... 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
Facts about Pearls
CaCO3 (aragonite, the outer layer) about 82 -
86%, conchiolin 10 - 14%, water 2%.
CRYSTALLOGRAPHY Aragonite is orthorhombic, with crystals
REFRACTIVE INDEX 1.53 - 1.69
HARDNESS 2.5 - 4.5
SPECIFIC GRAVITY 2.6 - 2.78.
HEAT SENSITIVE Yes
SPECIAL CARE INSTRUCTIONS Avoid heat and all chemicals,
including perfume and other cosmetics.
ENHANCEMENTS Dying, common