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Pearl
Name and Facts:
Pearls have been regarded as one of the most valuable gem materials. They have been used for
adornment for 6000 years. There is little difference between the cultured and natural pearls.
The derivation of the name is uncertain but maybe from a type of shell (Latin-Perna)
or from its spherical shape (Latin-Sphaerula). Pearls are produced by molluscs, rarely
by snails. They consists of mother-of-pearl, which is mainly calcium carbonite (in
the form of aragonite), and an organic horn substance (conchiolin) which are formed
concentrically around microcrystals. They have hardness in Mohs' scale around 3-4.
The specific gravity is 2.60-2.78 gr/cm3. The largest pearl ever found weighs 450
cts or 90 gr. It is in South Kensington Geological Museum in London.
This gem, a gift of the sea, has a myth and lore dating back to the beginning
of time. A Hebrew legend says that pearls were the tears of Eve after being banished
from the Garden of Eden. In America, it has been a long held tradition that a bride
receives a strand of pearls as a bride's gift to wear on her wedding day. Pearls are also
considered the birthstone for June along with Alexandrite.
Pearl Grading
Pearls are graded based on their nacre thickness, luster, surface texture, color, size, shape
and matching. A combination of these characteristics decides the overall quality and value of
pearls.
The nacre of a pearl has the unique luster called iridescence (or orient). The quality of
this luster is crucial to the grade of the pearl. Pearls are graded on the luster, surface
(smoothness with no pitting or blemishes), shape (spherical vs. all other shapes), and color.
Common designations for the four categories are AAA (extra fine), AA (fine), A (good), and BB
(commercial). AAA pearls would display superior characteristics in all areas while those of
a lesser grade would have luster, surface, shape, and color compromised to some degree in one or all
of those qualities.
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Grade
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Nacre
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Luster
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Shape
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Blemishes
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Matching
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A to A+ Quality
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Thin
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Medium
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Round
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Medium
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Medium
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AA to AA+ Quality
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Medium
to Thick
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Medium
to High
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Round
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Light
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Very
Good
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AAA
Quality
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Very
Thick to Extremely Thick
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Very
High to Extremely High
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Round
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Flawless
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Excellent
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Pearl are an interesting and complex subject. There are cultured, freshwater, Tahitian,
and South Sea pearls
Cultured Pearls
The increased demand for pearls has led to their cultivation. Such cultured pearls are
not imitation, but a natural product which has been produced with man's help. Today
cultured pearls amount to over 90% of the total pearl trade. A bid (mostly rounded mother
of pearl bid) is inserted into the mollusc.
Cultured pearls produce the finest pearls on the market today. Pearls are an organic gem
material that grows in an oyster. When a piece of the mantle or beard of an oyster of an
oyster is implanted into the heart of this mollusc the material that forms around it is
called nacre. Pearls are made up of layer upon layer of nacre. The longer these oysters
are left in he water, the larger the pearl grows, until it reaches capacity for that particular
type of oyster. Specific types of oysters are used to grow specific types of pearls.
Akoya Oyster
The Akoya oyster produces pearls from 2.0 mm - 10.0 mm, usually spherical in shape. The
usual color is white or cream in color, but pink and a deep rose pink are also achieved.
While Japan initiated the cultured pearl business, China has also become a major source.
Chinese Akoya pearls can be just as beautiful as their Japanese counterparts and usually
are less expensive. Akoya pearls are usually bleached, dyed or tinted to improve their color.
The most desirable shape is completely spherical
South Sea
South Sea cultured pearls are grown in the world's largest oyster. The pearls grown in
this oyster usually range from 9.0 mm - 18.0 mm or larger in size. Less than 1/3 of the
production of South Sea pearls are round making these pearls very rare and expensive.
White, light cream and gold are the most sought after colors of the South Sea Pearls.
Silver, yellow, blue and yellowish-orange are other colors available. South Sea pearls
are rarely dyed to improve their color.
Tahitian
Tahitian cultured pearls are grown in the warm waters of French Polynesia. A particular oyster,
the black-lipped oyster, is responsible for the exquisite size and color of Tahitian pearls. These
pearls grow from 8.0 mm - 14.0 mm or larger with less than half of the pearls being spherical in
shape. The most common shapes that are symmetrical but not round are ovals and drops. Non-symmetrical
baroque and semi-baroque shapes are also common. Tahitian pearls come in a glorious array of colors.
These include black, gray, brown, green, purple, and yellowish-green. Several colors are more highly
valued. The most highly valued color is peacock a combination of dark green-gray or blue-gray with
a rose or purple overtone. Aubergine (French for eggplant) is a very desirable grayish purple color.
Yellowish-green or greenish yellow pearls are called pistachio, another excellent color that is also
highly valued. Tahitian cultured pearls are rarely dyed to improve their color.
Freshwater Pearls
Freshwater pearls are grown in mussels, not oysters. Their production has given us a wealth of new
shapes-biwa, coin, button, etc. and every color of the rainbow. Many of these pearls are dyed to give us
these vibrant colors. The production of freshwater pearls is very high, making the cost very affordable
and providing a fun choice in jewelry.
How to Take Care of Pearls
Proper care of pearls is very important and they have some special characteristics. The porosity of
pearls are what enables them to be dyed. Never put pearls in an ultrasonic cleaner, water, soapy solutions
or jewelry cleaner. Chemicals can also be absorbed into the nacre causing discoloration. A good rule for
pearls is that they are the last thing you put on after you have applied perfume and/or hairspray and the
first thing you take off.
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