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Units
of Measurement
Unit for weighing gemstones is the carat. This is defined,
and is not to be confused with the term "karat"
used to describe the fineness of gold. Originally gems
were compared in weight with the seeds of various plants,
such as barley grain and the seeds of locust trees.
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The
word "carat" may derive from the Greek word
"keration."' At the time of the emperor Constantine
24 kerations made up a golden solidus. Since pure gold
is, by definition, 24 karat, the words –carat and "karat"
may thus be related in antiquity. |
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Since
different seeds were used to weigh gems in various locations,
there was no universal standard until 1907. In that year the
International committee on Weights and Measures proposed the
so-called "metric Carat” of 1/5 gram. This unit was adopted
in the United States in 1913 various other countries between
1908 and 1930. There are 28.3 grams in an ounce, so a carat
is equivalent to about .035 of an ounce. By comparison, a
United States copper penny weighs about 151/5 carats.
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DIAMONDS,
GEMSTONES & CRYSTALS
FACTS & FIGURES |
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carat is subdivided for convenience into 100 units
called points. A gem weight would be expressed
decimally as, for example, 11.36 carats, equivalent
to l l carats plus 36 points.For pearls, the unit
of weight is the grain. There are four grains
in a carat.
The price of pearls is calculated by a formula
that involves the weight and a so-called "base
price." The base price or base rate is affected
by both size and quality, and whether the pricing
is for matched pearls.
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Today
pearls are also measured in terms of diameter,
expressed in millimeters. A millimeter is about
.04 of an inch in length; a United States penny,
for example, measures 19mm in diameter. A pearl
weigh¬ing six grains is approximately 6mm
in diameter.
Faceted and cabochon-cut gemstones are also measured
in mil¬limeters, as well as carats. Millimeter
sizes are most often applied to synthetic and
lower-priced stones, but any good appraisal of
a gem would include both a weight and dimensions
in the description. Jewelry mountings are manufactured
to fit standard, or calibrated stones. |
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Because
such mountings are mass-produced and less costly than custom-made
settings, it is easier and less expensive to set a calibrated
stone than a free-size. Therefore, with less expensive gem
materials, calibrated stones command a slightly higher price
than random-sized gems. Finer gems are usually cut to conserve
weight.
Rough gem materials may be weighed in carats, if the value
of the rough is high; or in grams, ounces, or pounds for successively
less expensive material.
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