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Natural Pearls 2
in the case of a string of, say, a few dozen
to a hundre, so pearls, simple observation of their outward
appeara can be conclusive. In fact, although natural pearls
are most spherical, if one looks closely at a string of nat.
pearls, they nearly always appear to be bodies revel, about
an axis (along which the hole is drilled), slightly ' tened
at one or both poles, perhaps even tending to a lindrical
shape. On the other hand, most, although not cultured pearls
are more or less spherical, even when t~ have superficial
irregularities and protuberances. Thi_ because they consist
of few layers of nacre on a stn spherical support. Nonspherical
cultured pearls, which very similar in shape to most natural
pearls, do occur. : are not common and, as a rule, there will
be very few o string.
The physical properties of pearls are not ea•
measured (except for the density) and are not norm, used for
recognition; but, on average, natural pearls havslightly lower
density (2.71 g/cm3) than cultured pea (2.73-2.74 g/cm3).
Grayish natural pearls have a slower density (2.61 -2.69 g/cm3)
due to an excess of c, chiolin. To distinguish natural from
cultured pearls with a. certainty, specialist laboratories
use both radiography a the X-ray diffraction method, which
give precise inforr•tion on the arrangement of the internal
layers of nacre a the prismatic crystals of aragonite of which
they are co posed.
Occurrence Most of the few natural pearls
harvestnowadays come from the Persian Gulf, Sri Lanka, the
R Sea, and the Philippines; still smaller quantities are c
: lected from the sea off the coast of Venezuela and from
t• Gulf of California. In other places, such as the
seas Japan and along the northwest coast of Australia, the
dustry for cultured pearls has now developed to such :extent
that the possibility of finding natural pearls as weli disregarded.
Value One of the most valuable gems in antiquity,
pea, are still highly valued today, although not to the same
e~ tent. They are evaluated according to size, color, luste
regularity of form, compactness (the more watery, transl cent
ones are less durable, therefore less valuable). In tl case
of a number of pearls in a piece of jewelry, much a•
pends on their uniformity of color or, at any rate, how we
matched they are. A string of pearls of equal diameter worth
much more than one consisting of pearls of gra:: uated diameters
(larger at the center, smaller at the ends because numerous
pearls of a uniform size are harder - find.
Even a pair of matching pearls is worth more
tha double the price of a single pearl because of the quantitie
that have to be sorted to find two that are identical. 13,.
many natural pearls are old or antique and when they are ia
poor state of repair, dehydrated or cracked, brittle c yellowed
with age, their value is greatly reduced.
Simulants Cultured pearls
are not really imitations, b~. something much better. We shall,
therefore, be discussin:: these fully below. Pearls have been
imitated, at least sincthe mid-seventeenth century; hollow
spheres of thin glasc coated on the inside with a special
varnish made from fisscales, and usually filled with paraffin
or wax, were used For this reason, pearls were once tested
between thteeth: if they broke, they were clearly false.
They \&subsequently imitated by (solid or
hollow) spheres of gle or mother-of-pearl, varnished on the
outside in the sa way. All these imitations are very easily
recognizable if : served under a magnifying glass, which shows
the typi features of glass fusion around the hole, the paraffin
v. filling, and the translucent outer layer in one case, arc
the other, the minutely granular appearance of the spe. varnish
used. From a distance, however, they look s much like real
pearls, and there is a thriving industry them in both Japan
and Majorca.
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