Tahitian Pearls - Perles De Tahiti
Additional Information about Tahitian pearls
French Polynesia Official Classification
Tahiti Cultured Pearls are pearl concretions that are secreted inside
the black-lipped Pinctada Margaritifera species of pearl oysters
cultivated mainly in the lagoons of French Polynesia. They consist of
thick pearly layers containing organic substances and calcium carbonate
in the form of aragonite.
In French Polynesia, the trade designation "Tahiti Cultured Pearl" is
reserved exclusively for cultured pearls obtained from a grafting of
the locally cultivated Pinctada Margaritifera, variety cumingi pearl
oyster. Such pearls have a continuous pearly layer over at least 80% of
their surface and do not reveal either the underlying nucleus.
Tahiti Cultured Pearls are classified according to their diameter,
luster, shape, surface purity and color.
Tahitian Pearl - Diameter
Pearls are classified from millimeter to millimeter and measured by
the shortest diameter, which generally ranges between 8 and 14mm.This is
done by sorting them through sieves. Some pearls reach 16mm and very
exceptionally 18mm.To date, the record diameter for a round pearl is
21mm, 24,6mm for a semi-round, 26,95mm for a baroque pearl (Exhibited in
The Robert Wan Museum of The Pearl)
Tahitian Pearl - Lustre
This is the quality of the light reflections from the pearl's surface.
Pearls are said to have high, or very high, luster when the reflections
are bright and sharp. When the light reflections are weak and fuzzy (or
diffused), the pearls are described as dull. The Tahiti Cultured Pearl
rivals anything grown in Japan for the sharpness and intensity of
reflected light from a pearl's surface. In fact, pearls from French
Polynesia often possess such a mirror-like finish and radiant brilliance
that their overall appearance is likened to that of very shiny metallic
objects, such as ball bearings.
The only problem with such an analogy is that it suggests a cold,
steely beauty. In reality, lustrous Tahiti Cultured Pearls have warmth
to them--even when their surfaces gleam as brightly as a dress shoe.
Regardless, the lustre of the tahitian cultured pearl is just like their
color--all natural.
Shape
Four basic shapes are defined at the production stage:
- round
and semi-round,(see photo 1)
- drop, button and oval(see
photo 2)
- semi-baroque and baroques(see photo 3)
- and
ringed or circled.(see photo 4)
For some jewelery
makers, shape is purely a design element, be it the sensuous curves of
the drop or the flowing free-form lines of many baroque shapes. For such
artists, all shapes that inspire them share aesthetic equality.
Most
designers agree it is difficult to favor one kind of shape over
another.
A New York designer once said: "A pearl that looks homely
seen loose will be transformed into a thing of beauty if placed in the
right setting."
Round pearls
Round pearls are almost perfect spheres whose
diameter variation rate is less than 2%.
The round pearl is the most
sought after and the most rare of Tahiti cultured pearls.
Because
Tahiti Cultured Pearls are most commonly used in jewelry, the low
incidence of rounds is not considered a drawback. On the contrary, the
wide variety of affordable fancy shapes is a big drawing card for
jewelers who specialize in them.
Semi-round pearls
Semi-round pearls are slightly imperfect
spheres whose diameter variation rate is greater than 2% but less than
5%.
When a pearl is allowed two years to grow inside an oyster, the
chances of even, perfectly spherical nacre accumulation are a long shot.
One experienced seller of fine Tahiti Cultured Pearls says true rounds
rarely account for more than 10% of a Tahiti Cultured Pearls farm's
crop. And 5% is more the norm.
Drop, button and oval pearls
The drop or pear presenting at
least one axis of symmetry.
The button presenting at least one
axis of symmetry.
The oval presenting at least one axis of
symmetry.
Semi-baroque and baroque pearls
The semi-baroque in the
strict sense presenting at least one axis of revolution.
The
baroque pearl is generally an uneven pearl wich does not fall in any of
the above categories.
Ringed or circled pearls
Ringed or circled pearls are
characterized by regular streaks or concave rings perpendicular to an
axis of revolution over more than the upper third of the pearl's
surface.
Quality
This is determined by observing the special features
of the pearl's surface and luster. But nacre thickness, color, shape and
size also judge quality.
Nacre Thickness
This affects the durability and sometimes the
beauty of a Tahiti cultured pearl.If a cultured pearl starts off with a
thick coating of nacre (and gets reasonable care), its beauty will last
a life time.
If, however, the pearl has a thin nacre coating (or
is carelessly treated), its nacre will soon wear away, exposing the
nucleus.
The French Polynesian Government has set up a minimum
nacre thickness of 0,8mm to the Tahiti Cultured Pearl. All pearls
showing less than 0,8mm thickness are banned for marketing and
destroyed.
Surface
For reasons best understood by psychologists, pearl
dealers talk about the degree to which a pearl's skin is free of blemish
as "spotting", a very negative term for a very common pearl feature.
Tahiti
cultured pearl farmers generally use four ratings for surface quality:
A, B, C and D. Pearl dealers prefer the neutral term "surface" as a way
of discussing--or even rating--the presence or absence of imperfections
in pearls. In this regard, it is the pearl word equivalent of "clarity".
Top Gem
Flawless pearl.
Excellent luster.
Quality A
An "A Quality" pearl is a flawless pearl on at
least 90% of it surface : on the remaining 10%, the pearl may have some
slight concentrated imperfections with one or two deep imperfections
tolerated. At least a very high luster.
Quality B
A "B Quality" pearl is a flawless pearl on at least
70% of its surface. On the remaining 30%, the pearl may have some
slight concentrated imperfections with one or two deep imperfections
tolarated. At least a high luster.
Quality C
A "C Quality" pearl is a flawless pearl on at least
40% of its surface. On the remaining 60%, the pearl may have some
slight concentrated imperfections with a 10% of deep imperfections
tolerated. At least a medium luster.
Quality D
A "D Quality" pearl is one that has either a large
amount of slight flaws distributed over 60% of the surface, or several
slight and deep flaws distributed over 60% of the surface at the most,
regardless of the luster.
Color
Tahiti Cultured Pearls offer an extensive array of
colors and they all are natural. This is what makes their precious
difference.
They generally have a body color enriched by at least
one overtone color. There exists a wide range of body colors, the
predominant basic colors of a Tahiti Cultured Pearl being: black, grey,
blue, green and brown. Overtone colors on dark-colored pearls are pink,
blue, gold, silver and a reddish purple. These overtones may be present
in a variety of combinations and are considered a plus factor. Specific
names are given to those colors:
- "Peacock" : greenish black
- "Cherry" or "Aubergine" : purplish black
- "Champagne": yellowish
grey
- "Pistachio" : greenish grey
- "Lavender" : bluish black
- "Tahitian gold" : golden black
- "Pigeon grey" : purplish grey
- "Silver" : grey
- "Moon grey" : pale grey
- "Orient grey" :
surface iridescence
Imitation Pearls
At
one time, if a cultured pearl was black it was certainly stained
artificially, usually by immersion in a solution of silver nitrate.
Natural
black pearls do occur, although more rarely than ever, while
naturally-colored black cultured pearls from Tahiti and other places are
increasingly common due to the use of the black-lipped pearl oyster
known as the Pinctada Margaritifera.
However, imitation black
pearls are not so common as other color imitations since the true black
pearl has a color that is far from being a matte black. In fact, the
natural and cultured black pearl both have a beautiful sheen. Sometimes
this sheen is a greenish hue against a black background. At other times
the sheen is a bluish-black color that is very difficult to adequately
describe.
Thus, because of the richness and diversity of their
hues or overtones, Tahiti Cultured Pearl colors are very difficult to
artificially reproduce. Yet, imitation black colored pearls do exist.
5 ways to detect
imitation pearls
Faint Reddish Glow Characterizes Natural Black
Pearls
Natural black pearls have a faint reddish glow when viewed
through crossed filters, such as when bathed in blue light from a
copper sulphate solution and examined through a red filter.
Artificially-stained black pearls do not have this red glow reaction. It
has been found that overlong exposure to X rays will blacken some
freshwater pearls without a nucleus. But this is not so serious as
possible blackening of natural pearls.
Some Imitations Have
Immediate Giveaway Signs
Imitation pearls are found in graduated
and chocker necklaces of such sizes and matching symmetry and color as
to be obviously anything but natural or cultured pearls. The immediate
giveaway reason is that so many large, perfectly matched pearls would
cost a small fortune. But less pretentious imitations still have a
giveaway sign. That is the drill hole. It is never so precise in
imitation pearls as it is in natural or cultured pearls, which are
individually drilled. The mass-produced imitation pearls literally have
their hallmark at the drill hole, which shows signs of uneveness and
rough formations due to the lack of finish applied to the manufactured
pearl. Thick "tears" of the coating may appear at the drill hole as
coagulations.
10x Lens Easily Reveals Imitations
Such
telltale signs are quickly and easily revealed when an examination of
the suspected imitation pearl is made with a 10x lens. Equally, an
examination of the surface of glass beads will reveal bubbles just below
the surface, or a mat pattern totally unlike the wandering serrated
cloissons seen in natural pearls. Likely candidates for treated,
imitation black pearls are the hard-to-sell, less popular colors. The
typical treatment uses a solution containing a silver salt, such as
silver nitrate. The pearl oyster picks up a silver precipitate, which is
blackened by exposure to light or hydrogen sulfide gas. The treated
color is non-fading.
Ways of Detecting Treated Color Pearls
The
treated color can be detected by a number of tests, such as certain
types of X-ray analysis and infrared photography. Such tests detect the
treated color's comparative lack of ultraviolet fluorescence and its
response to dilute acids.
Official International Definition
History and Role of the
CIBJO
The CIBJO was created in 1961 by 10 nations that ratified
new statutes and transformed a confederation (BIBOAH) that was
originally formed in the early 1920s by several European countries to
represent the interests of the jewellery trade.
More than 20
countries belong to the CIBJO, which has four independent sectors:
manufacturing of jewellery and silverware; wholesaling of jewellery and
silverware; dealing and cutting of diamonds, gemstones and pearls; and
retailing of jewellery and silverware.
The CIBJO has three
intersectorial commissions. One is for diamonds, one for gemstones and
one for pearls. They meet periodically to revise and update three books
defining the nomenclature and rules of application for good trade
practices.
CIBJO Definition of a Cultured Pearl
What is
the official definition of a cultured pearl such as what is produced in
Tahiti and Her Islands?
The International Confederation of
Jewellery, Silverware, Diamonds, Pearls and Stones (CIBJO) has defined
the cultured pearl in its "Pearl Book" as follows: "Cultured pearls are
nacreous formations secreted in the interior of the productive molluscs.
The outer layers of cultured pearls are composed of concentric layers
of an organic substance (a scleroprotein named conchiolin) and of
calcium carbonate (usually in the form of aragonite). "The secretion of
nacreous layers is caused by the metabolism of living molluscs
themselves; human intervention only started the secretion. This applies
to all cultured pearls whether with a solid nucleus and/or an organic
implant. "
Other Types of Cultured Pearls The CIBJO's "Pearl
Book" also defines other types of cultured pearls. There are "cultured
three-quarter pearls or cultured half pearls", which have been
"deliberately cultivated to a 3/4 or 1/2 round shape with nacreous
layers by molluscs."
There are composite cultured pearls, which
are "products resulting from man's assemblage of an upper portion of
cultured pearl and one or more lower portions of the same or other
substances.
Natural Pearls
The CIBJO defines natural
pearls as those "natural formations secreted accidentally and without
the aid of any human agency, in the interior of molluscs. They are
composed of an organic substance (a scleroprotein named conchiolin) and
of calcium carbonate (usually in the form of aragonite) arranged in
concentric layers, the outer most of which are nacreous. The exception
being the conch pearls where the layers are radial."
Note: Images and content courtesy PERLES DE TAHITI
