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Gemological Information
Pearls
Understanding Pearls
A pearl is created by a mollusk when an irritant causes it to secrete alternating
layers of material, called "conchiolin" and "nacre", to coat the
invader and make its presence less bothersome. This irritant forms the nucleus of
the pearl. With natural pearls, this irritant is probably a parasite or a piece of debris
that the animal is unable to wash away. Nearly all pearls on the market are
"cultured" pearls, where a relatively large bead is placed in the body of the
host oyster (cultured saltwater pearls) or a small piece of tissue from a fresh water
mussel is inserted into another mussel to stimulate pearl formation (freshwater pearls).
Pearls are classified by Origin, then graded by size,
shape, nacre thickness, color, luster, surface clarity and matching. These qualities are
not considered equal. Some factors will be weighted to give them more influence in
arriving at a final grade. A very thin nacre thickness, for example, could never yield a
fine quality pearl.
Grading is relative to the best attainable quality for the type. For example, South Sea
pearls, which grow in warmer water for longer periods of time, generally have a lower
luster and more tiny blemishes than Japanese Akoya pearls, that grow in colder water and
for shorter periods of time. South Sea pearls are graded against each other, not by what
would be expected for a similar quality Akoya pearl.
Origin:
- Cultured (Akoya)- the traditional cultured pearl, farmed almost exclusively in
Japan.
- South Sea cultured - Large cultured pearls from Tahitian and other
South Sea waters including Australia, these are mostly white to silver-white, gray and
golden in color. They are grown in the Margaretifera oyster, and are considerable
larger than the Japanese Akoya oyster pearl.
- Tahitian cultured- Gray to black colored pearl cultivated in the black-lipped
variety of Margaretifera oyster found in the south Pacific.
- Freshwater cultured- nucleated with tissue only, with no bead nucleus, these
mostly irregular, colorful pearls are farmed in Japan, China and the United States, among
other locations. They are nurtured in freshwater mussels rather than oysters.
- Novelty- pearl-like concretions formed by mollusks other than oysters and
mussels, such as abalone, clam or conch.
- Natural- occurring naturally in the mollusk without assistance from man. Also
referred to as "Oriental" pearls. These now constitute only a tiny portion of
the pearl market.
Size:
A large pearl can be produced only by a mollusk
large enough to hold it. Thus, the pearl farmer has a significant investment in raising
the mollusk before it can even be nucleated. Because of this, size is a significant factor
in valuing pearls.
Shape: This refers to the roundness or symmetry of the pearl.
Round pearls are the rarest and most highly prized. Even though they start with a round
bead, the action of the mollusk and movement of the water usually cause the pearl to
become a shape other than perfectly round. Symmetrical pearls of other pleasing shapes are
rated for symmetry, but priced according to a different scale from rounds.
- Round - Rated as Round-in-all, Mostly Round, Slightly Off-Round,
Off-Round and Semi-Baroque. (Baroque pearls are considered a separate category.)
- Drop - a pear- or teardrop shaped pearl. The more symmetrical, the
higher the quality.
- Barrel - more or less cylindrical, with blunt ends.
- Ringed - pearls that have developed attractive grooves by being turned
round and round in the oyster in one place.
- Baroque - pearls with a pleasingly organic shape, without
tags or sharp tails.
Nacre Thickness: Nacre is the single most important
factor in the beauty and durability of the pearl. If you can see the bead through the
nacre, or if it is cracked or peeling or has chalky-looking patches, it is a very low
grade pearl. Some pearls with thin nacre have high luster and are free of blemishes,
because they have been left in the water for only a brief time. This thin surface will
soon be damaged by normal wear, and may chip or peal around the drill hole. Always look
for pearls with at least Medium nacre, at least 0.35 mm thick.
Luster: The brightness, or reflectivity of the pearl. The
very top pearls have a metallic luster, while fine pearls have a sub-metallic luster but
still reflect objects sharply on the surface. Low-luster pearls display very little if any
reflectivity.
Color:
- Body color - the base color of the pearl, observable near the outer
edges of the pearl.
White and silver-white are the preferred colors, with grays and cream colors being less
desired. However, color is a personal preference and should be chosen to complement skin
tone.
- Overtone - one or more colors that may (or may not) overlay the body
color. Best observed just off the dome of the pearl. Pink overtones are preferred, with
green and other colors less desirable.
- Orient - play of color, or iridescence seeming to move about the
surface of some pearls. It is a rare component, more often seen on irregular surfaces.
Surface blemishes, or texture: Surface blemishes, or texture refers to blemishes or
spotting on the surface of the pearl. They are graded by their size, type, number,
location and visibility.
Matching: refers to pairs or strands, and addresses
uniformity of color, luster, shape, spotting and graduation. If colors are intentionally
mixed, it refers to the attractiveness of the combination. Even in uniform
strands, there will be gradation in size from the center pearl to those at the ends. Each
pearl in a strand has been selected to be placed between its neighbor on each side, and
there should be no noticeable difference between pearls that are side-by-side. Bead
stringer not trained in stringing pearls may inadvertently re-string pearls in the
incorrect order, disrupting the imperceptible blend of one pearl to the next
and decreasing the value of the strand.
Pearl mounting/stringing:
a perfectly blemish-free pearl is
usually not drilled, but rather is mounted in prongs or glued in place. If the pearl is
perfectly "clean" except for one blemish, a drill hole will be placed through
the blemish. Pearl beads are drilled though one, or sometimes two blemishes, to yield the
best quality possible. Pearl strands should be knotted to prevent them from wearing
against each other and to reduce loss in case the strand breaks. Knots should be tight
against the pearl. If a pearl can slide between knots, it is a sign that the string has
stretched and needs to be replaced. If a mounted pearl begins to wobble or turn, stop
wearing it immediately and take it to your jeweler to have it re-glued.
Condition:
The surface of the pearl should be smooth and not
abraded by chemicals such as perfume, hair spray, and skin acids. There should be no
peeling or cracking of the nacre layer around the drill hole. Pearls that have been stored
in a safe deposit box for long periods may have yellowed.
Pearl care: Protect pearls from chemicals and abrasion.
Pearls are very soft, and are easily damaged by other jewelry. Most dust contains much
harder quartz particles. Thus, pearls are easily scratched by careless cleaning. Keep
pearls in their own soft case or bag, and wait to put them on until your hair, make-up and
perfume have all been applied. After wearing them against the skin, wipe pearls gently
with a very soft, damp cloth before returning them to their secure haven. As pearls seem
to benefit from exposure to the light, remember to wear them often!
PEARL GRADING NOMENCLATURE
Pearls are classified by Origin, then graded by size, shape, nacre
thickness, color, luster, surface clarity and matching. These factors are weighted
to arrive at a final grade.
Size: Limited by the mollusk used in cultivation, size is a very significant factor
in valuing pearls.
Shape: Refers to the symmetry and form of the pearl. Fancy shaped pearls, such as
drops, buttons, coin, barrel, ringed (ridged) etc. are graded according to their symmetry
and balance.
(Rounds)
All Round |
Mostly Round |
Slightly Off-Round |
Off-Round |
Semi-Baroque |
10 |
9 7 |
6 4 |
3 2 |
1 |
All perfectly
round |
Most perfectly
round |
Some may be
round |
Most are not
round |
All off-round or
irregular |
(Baroques)
Irregular shape, no tail |
Slight tail |
Heavy tail |
10 8 |
7 4 |
3 1 |
Nacre Thickness: Nacre is the single most important factor in the beauty and
durability of the pearl Some pearls with thin nacre have high luster and are free of
blemishes, because they have been left in the water for only a brief time. This thin
surface will soon be damaged by normal wear, and may chip or peal around the drill hole.
Very Thick |
Thick |
Medium |
Thin |
Very Thin |
10 |
9 7 |
6 4 |
3 2 |
1 |
2 Years
Cultivation |
1 ˝ - 2 Years |
1 1 ˝
Years |
9 mo. 1
Year |
Under 9 months |
0.50 mm |
0.49
0.34 mm |
0.35 mm |
0.34
0.25 mm |
0.25 mm or
less |
Luster: The brightness, or reflectivity of the pearl. The very top pearls have a
metallic luster, while fine pearls have a sub-metallic luster but still reflect objects
sharply on the surface. Low-luster pearls display very little if any reflectivity.
Very High |
High |
Medium |
Low |
Very Low |
10 |
9 8 |
7 5 |
4 2 |
1 |
Color: Color is described by the base color of the pearl, called body color,
and any additional colors that may be overlaying the base color, called overtone.
These grades reflect demand in the US market, but pearls should be selected to complement
the skin tones of the person who will be wearing them.
Body
Color |
White |
Pink |
White |
Light Cream |
White |
Medium Cream |
Pink |
Med. Cream |
Dark Cream |
Dark Cream |
Yellow |
Yellow |
Overtone
|
Rose |
Rose |
None |
Rose |
Green |
Rose |
Green |
None / Green |
Rose |
None / Green |
Green / Rose |
None |
Grade |
10 9 |
10 9 |
8 7 |
8 7 |
7 6 |
6 5 |
5 4 |
4 3 |
4 3 |
4 3 |
3 2 |
2 - 1 |
Surface blemishes, or texture: refers to blemishes or spotting on the surface of
the pearl. They are graded by their size, type, number, location and visibility.
Unblemished |
Very Slight |
Slight |
Blemished |
Very Blemished |
10 |
9 7 |
6 4 |
3 2 |
1 |
Matching: refers to pairs or strands, and addresses uniformity of color, luster,
shape, spotting and graduation. If colors are intentionally mixed, it refers to the
attractiveness of the combination. Each pearl in a strand has been selected to be placed
between its neighbor on each side, and there should be no noticeable difference between
pearls that are side-by-side.
Excellent |
Very Good |
Good |
Fair |
Poor |
10 |
9 7 |
6 4 |
3 2 |
1 |
|
|