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A pearl is a hard, roundish object produced within the soft tissue (specifically
the mantle) of a living shelled mollusk. Just like the shell of mollusks, a pearl
is composed of calcium carbonate in minute crystalline form, which has been
deposited in concentric layers. The ideal pearl is perfectly round and
smooth, but many other shapes of pearls (baroque pearls) occur. The finest
quality natural pearls have been highly valued as gemstones and objects of
beauty for many centuries, and because of this, the word pearl became a
metaphor for something very rare, very fine, very admirable and very
valuable.

Valuable pearls occur in the wild, but they are very rare. Cultured or farmed
pearls make up the majority of those that are currently sold. Pearls from the
sea are valued more highly than freshwater pearls. Imitation or fake pearls
are also widely sold in inexpensive jewelry, but the quality of the iridescence
is usually very poor, and generally speaking, fake pearls are usually quite
easy to distinguish from the real thing. Pearls have been harvested, or more
recently cultivated, primarily for use in jewelry, but in the past they were also
stitched onto lavish clothing, as worn, for example, by royalty. Pearls have
also been crushed and used in cosmetics, medicines, or in paint formulations.

In several European languages, the word "pearl" is synonymous with "bead",
which can lead to confusion during translation.


Definition of a Pearl
Almost any shelled mollusk can, by natural processes, produce some kind of
"pearl" when an irritating microscopic object becomes trapped within the
mollusk's mantle folds, but the great majority of these "pearls" are not valued
as gemstones. Nacreous pearls, the best-known and most commercially-
significant pearls, are primarily produced by two groups of molluscan
bivalves or clams. A nacreous pearl is made from layers of nacre, by the
same living process as is used in the secretion of the mother of pearl which
lines the shell.

A "natural pearl" is one that forms without any human intervention at all, in
the wild, and is very rare. Many hundreds of pearl oysters or pearl mussels
have to be gathered and opened, and thus killed, in order to find even one
wild pearl, and for many centuries that was the only way pearls were
obtained. This was the main reason why pearls fetched such extraordinary
prices in the past. A cultured pearl, on the other hand, is one that has been
formed on a pearl farm. In modern times however, almost all the pearls for
sale were formed with the aid of human pearl farmers. The great majority of
pearls on the market are cultured pearls.

One family of nacreous pearl bivalves, the pearl oysters, lives in the sea
while the other, very different group of bivalves live in freshwater; these are
the river mussels such as the freshwater pearl mussel. Saltwater pearls can
grow in several species of marine pearl oysters in the family Pteriidae.
Freshwater pearls grow within certain (but by no means all) species of
freshwater mussels in the order Unionida, the families Unionidae and
Margaritiferidae.

Physical Properties
The unique luster of pearls depends upon the reflection, refraction, and
diffraction of light from the translucent layers. The thinner and more
numerous the layers in the pearl, the finer the luster. The iridescence that
pearls display is caused by the overlapping of successive layers, which
breaks up light falling on the surface.
In addition, pearls (especially cultured freshwater pearls) can be dyed
yellow, green, blue, brown, pink, purple, or black.

Freshwater and Saltwater Pearls
Freshwater and saltwater pearls may sometimes look quite similar, but they
come from very different sources.
Natural freshwater pearls form in various species of freshwater mussels,
family Unionidae, which live in lakes, rivers, ponds and other bodies of fresh
water. These freshwater pearl mussels occur not only in hotter climates, but
also in colder more temperate areas such as Scotland: see the freshwater
pearl mussel. However, most freshwater cultured pearls sold today come
from China.

Saltwater pearls grow within pearl oysters, family Pteriidae, which live in
oceans. Saltwater pearl oysters are usually cultivated in protected lagoons
or volcanic atolls.

Creation of a Pearl
The difference between natural and cultured pearls focuses on whether the
pearl was created spontaneously by nature — without human intervention —
or with human aid. Pearls are formed inside the shell of certain mollusks: as
a defense mechanism to a potentially threatening irritant such as a parasite
inside its shell, the mollusk creates a pearl to seal off the irritation.
The mantle of the mollusk deposits layers of calcium carbonate (CaCO3) in
the form of the mineral aragonite or a mixture of aragonite and calcite (both
crystalline forms of calcium carbonate) held together by an organic horn-like
compound called conchiolin. The combination of aragonite and conchiolin is
called nacre, which makes up mother-of-pearl. The commonly held belief
that a grain of sand acts as the irritant is in fact rarely the case. Typical
stimuli include organic material, parasites, or even damage that displaces
mantle tissue to another part of the animal's body. These small particles or
organisms enter the animal when the shell valves are open for feeding or
respiration. In cultured pearls, the irritant is typically a cut piece of the
mantle epithelium, together with processed shell beads, the combination of
which the animal accepts into its body.

Natural Pearls
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,
being irritated by the intruder, 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.

Value of a Natural Pearl
Quality natural pearls are very rare jewels. The actual value of a natural
pearl is determined in the same way as it would be for other "precious"
gems. The valuation factors include size, shape, quality of surface, orient
and luster.
Single natural pearls are often sold as a collector's item, 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.
Yachtsman and financier Cartier purchased the landmark Cartier store on
Fifth Avenue in New York for $100 cash and a double strand of matched
natural pearls valued at $1 million.

Origin of a Natural Pearl
Previously natural pearls were found in many parts of the world. Present day
natural pearling is confined mostly to seas off Bahrain. Australia also has
one of the world's last remaining fleets of pearl diving ships. Australian pearl
divers dive for south sea pearl oysters to be used in the cultured south sea
pearl industry. The catch of pearl oysters is similar to the numbers of
oysters taken during the natural pearl days. Hence significant numbers of
natural pearls are still found in the Australian Indian Ocean waters from wild
oysters. X-Ray examination is required to positively verify natural pearls
found today.

Cultured Pearls
Cultured pearls (nucleated and non-nucleated or tissue nucleated cultured
pearls) and imitation pearls can be distinguished from natural pearls by X-ray
examination. Nucleated cultured pearls are often 'pre-formed' as they tend to
follow the shape of the implanted shell bead nucleus. Once the pre-formed
beads are inserted into the oyster, it secretes a few layers of nacre around
the outside surface of the implant before it is removed after six months or
more. It is the nacre that gives pearls their beautiful luster and color.

When a nucleated cultured pearl is X-rayed, it reveals a different structure to
that of a natural pearl. A cultured pearl shows a solid center with no
concentric growth rings, whereas a natural pearl shows a series of
concentric growth rings.

Gemological Identification
A well equipped gem testing laboratory (e.g. SSEF, Guebelin, GIA, AGTA)
is able to distinguish natural pearls from cultured pearls by using a
gemological x-ray in order to examine the center of a pearl. With an x-ray it
is possible to see the growth rings of the pearl, where the layers of calcium
carbonate are separated by thin layers of conchiolin. The differentiation of
natural pearls from tissue-nucleated cultured pearls can be very difficult
without the use of this x-ray technique.

Natural and cultured pearls can be distinguished from imitation pearls using a
microscope. Another method of testing for imitations is to rub the pearl
against the surface of a front tooth. Imitation pearls are completely smooth,
but natural and cultured pearls are composed of nacre platelets, which feel
slightly gritty.

Different types of Cultured Pearls, including Black Pearls
Black pearls, frequently referred to as Black Tahitian Pearls, are highly
valued because of their rarity; the culturing process for them dictates a
smaller volume output and can never be mass produced. This is due to bad
health and/or non-survival of the process, rejection of the nucleus and their
sensitivity to changing climatic and ocean conditions. Before the days of
cultured pearls, black pearls were rare and highly valued for the simple
reason that white pearl oysters rarely produced naturally black pearls, and
black pearl oysters rarely produced any natural pearls at all.

Since the development of pearl culture technology, the black pearl oyster
found in Tahiti and many other Pacific Island area has been extensively used
for producing cultured pearls. The rarity of the black cultured pearl is now a
"comparative" issue. The black cultured pearl is rare when compared to
Chinese freshwater cultured pearls, and Japanese and Chinese akoya
cultured pearls, and is more valuable than these pearls. However, it is more
abundant than the South Sea pearl, which is more valuable than the black
cultured pearl. This is simply because the black pearl oyster Pinctada
margaritifera is far more abundant than the elusive, rare, and larger south
sea pearl oyster - Pinctada maxima, which cannot be found in lagoons, but
which must be dived for in a rare number of deep ocean habitats or grown in
hatcheries.

Black cultured pearls from the black pearl
oyster — Pinctada margaritifera — are
not South Sea pearls, although they are
often mistakenly described as black South
Sea pearls. In the absence of an official definition for the pearl from the
black oyster, these pearls are usually referred to as "black Tahitian pearls".

The correct definition of a South Sea pearl — as described by CIBJO and
the GIA — is a pearl produced by the Pinctada maxima pearl oyster. South
Sea pearls are the color of their host Pinctada maxima oyster — and can be
white, silver, pink, gold, cream, and any combination of these basic colors,
including overtones of the various colors of the rainbow displayed in the pearl
nacre of the oyster shell itself.


Mabe Pearls
Cultured mabes are grown intentionally, by using a hemispheric nucleus,
rather than a round one; and by implanting it against the oyster's shell, rather
than within its tissue. The pearl then develops in a hemispheric form, with a
flat back. While in the oyster a mabe pearl is actually considered a blister
pearl not a mabe pearl.

Creating Mabe Pearls
After the blister pearl has developed, it is 'worked' to become a mabe pearl.
Blister pearls are ‘worked’ by cutting the pearl out of the shell with a circle-
bit drill. The nucleus is then removed and replaced with a resin. The back of
the pearl is then capped with a piece of mother-of-pearl to complete the
mabe pearl.

Shapes
  • Round
  • Round pearls are
    perfectly spherical --
    the shape most people
    think of when they
    think of a pearl. Because of their relative rarity and "classic" nature, they
    are highly desirable. Round pearls fall into the spherical category.

  • Off-Round
  • The term off-round is used to describe pearls which are 'roundish' to the
    eye but have a slightly oval or flattened shape. They can still have
    excellent qualities in terms of lustre or lack of blemish but being off-
    round makes them less expensive.

  • Teardrop (pendant)
  • Drop pearls are pear- or teardrop-shaped. The drop can either be
    "long" or "short," depending on its proportions. These pearls make
    attractive earrings or pendants. This is also a symmetrical shape.

  • Button
  • Button pearls are flattened to some degree, making them resemble a
    button or perhaps a disk rather than a perfect sphere. These pearls are
    often used in earrings, where the flattened side can be attached to the
    setting. Buttons are also categorized as symmetrical.

  • Oval
  • These pearls are shaped like an oval -- narrower at the ends than they
    are in the center. Ovals are categorized as a symmetrical shape.

  • Circle
  • Some Pearls for develop with one or more grooves or rings encircling
    them. These pearls are known as ringed or circled. This adjective can
    be attached to the primary shape in order to more fully describe the
    pearl, such as "circled round" or "ringed oval."

  • Baroque
  • This is a pearl which is both non-symmetrical and irregular in shape.  
    The baroque pearl can be purely abstract in its shape, or it can
    resemble a cross, stick; or some other shape.

  • Semi-baroque
  • These pearls are slightly irregular in their shape. For example, a pearl
    which might otherwise be considered an oval, button, or drop pearl, but
    which is not symmetrical in nature, would be considered semi-baroque.
    Semi-baroque pearls fall into the baroque category of shapes.

Color
The general color of a
pearl is also called the
body color.
Typical pearl colors are
white, cream, yellow,
pink, silver, or black. A pearl can also have a hint of secondary color, or
overtone, which is seen when light reflects off the pearl surface. For
example, a pearl strand may appear white, but when examined more
closely, a pink overtone may become apparent.

Luster
Pearls produce an intense, deep shine called luster. This effect is created
when light reflects off the many layers of tiny calcium carbonate crystals that
compose the pearl. This substance is called nacre. When selecting a pearl,
consider that the larger the pearl, the more nacre it has, so it will also exhibit
even more luster. Compare a 5mm Freshwater cultured pearl with a 10mm
South Sea cultured pearl and the difference in the amount of nacre is
obvious. The difference in luster is as clearly visible as the difference in the
pearl sizes
.

Size
The size of the pearl greatly depends on the type of pearl. Freshwater
pearls range in size from about 3.0–7.0mm, Akoya pearls range from about
6.0–8.5mm, and South Sea and Tahitian pearls can reach sizes as large as
13mm
.


Pearl Surface
One of the main determiners of a pearl's value is the quality of its surface.  
Most pearls have some kind of natural blemishes such as pits, bumps, spots
of other colors or dullness and tiny surface cracks.  The fewer of these
imperfections a pearl has on its surface, the more valuable the pearl.  

Natural pearls normally have more flaws than cultured Japanese Akoya
pearls. That's because they' ve been in the oyster longer and have had more
time to develop blemishes. Cultured pearls from the South Seas are also
more likely to have flaws than Akoyas, which have a thinner nacre coating
.
                     
Pearl Care
When cared for properly, pearls can last a lifetime. The best way to care for
pearls is to wear them often as the body’s natural oils keep pearls lustrous.
However, it's important to keep them away from household chemicals
including perfume, makeup and hairspray. Chemicals found in these common
products can dull the luster of your pearls. It is recommended that you put
your pearls on last when getting ready and make them the first thing you
take off when you come home. Before putting your pearls away, wipe them
with a soft cloth and store them separate from other jewelry to avoid
scratching their tender surfaces