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4 C's of Diamonds - Carat
History of the Carat
Weighing commodities as small and precious as gems demands
a very small, uniform unit of weight. To meet this need,
early gem traders turned to plant seeds that were reasonably
uniform in size and weight. Two of the oldest were wheat
grains and carob seeds. Both were common in the gem-producing
and trading areas of the ancient world. Wheat was a
dietary staple, and indidual wheat grains provided a
plentiful and relatively uniform weight standard. Our
modern pearl grain, troy grain, and avoirdupois and
apothecaries' grains all derived from the wheat grain.
(Diamond weights are sometimes approximated in grains).
The carob, or locust tree, produces edible seed pods
that are still important as feed for livestock and as
a flavoring. Traders used the inedible seeds as a standard
weight from which our modern metric carat evolved.
Carat weight was standardized in the early twentieth
century. If you had purchased a 'one-carat' diamond
in 1895, it might have weighed anywhere from 0.95 to
1.07 metric carats, depending on where you bought it.
But between 1908 and 1930, the standard metric carat
was adopted throughout most of Europe and in Japan,
Mexico, South Africa, Thailand, the USA, and the USSR.
Consumers sometimes confuse the terms carat and karat.
Although in some countries the two are synonymous, in
the US, karat refers to the fineness of gold alloys
(pure gold is 24 karat; 14 karat is 14 parts gold and
10 parts other metal or metals) and carat refers to
gem weights.
Carat Weight
When you tell people one diamond weighs more than
another, they usually understand what you mean-but few
consumers realize how precisely diamonds are weighed.
Like most gems, diamonds are weighed in metric carats;
one carat equals 0.2 gram-a little more than 0.007 (seven
thousandths) ounce avoirdupois.In other words, it takes
almost 142 carats to equal 1 ounce. But even this is
not precise enough for something so precious. Even with
relatively inexpensive diamonds, fractions of a carat
can represent hundreds of dollars (thousands, with top-quality
stones). For this reason, in the diamond industry, weight
is measured to a thousandth of a carat and rounded to
the nearest hundredth (or point).
To visualize how precise this is, consider that a point-a
hundredth of a carat-is less than one fourteen-thousandth
of an ounce. The term point can confuse consumers, who
may think you are referring to the number of facets
on the stone, or to the decimal point specifying hundredths.
Rules and Industry Practice
The FTC's Trade Practice Rules for the jewelry Industry
(1957) state:
RULE 32: Misrepresentation of Weight, "Total Weight"
(a) It is an unfair trade practice to misrepresent the
weight of any diamond or to deceive purchasers or prospective
purchasers as to the weight of any diamond (Note: The
standard unit for designation of the weight of a diamond
is the carat, which is equivalent to two hundred miligrams
(1/5 gram). While advertisements may state the range
of weights of a group of products, all weight representations
regarding individual products shall be subject to a
1/200th of a carat (one-half "point") tolerance.)
(b) It is an unfair trade practice to state or otherwise
represent the weight of all diamonds contained in a
ring or other article of jewelry unless such weight
figure is accompanied with equal conspicuity by the
words "total weight," or words of similar
import, so as to indicate clearly that the weight shown
is that of all stones in the article and not that of
the center or largest stone. Apparently, this guideline
was inadvertently omitted from the FTC Guides for the
jewelry Industry (1979). It will probably be reinstated
in future revisions. The rule regarding representation
of total weight is fairly plain: If you are showing
a piece of jewelry set with more than one gem, be sure
you are clear in your description of the weights of
individual stones.
The "half-point" tolerance means that, in
the US, weight must legally be measured to a thousandth
of a carat (0.001) and rounded to the nearest hundredth
(0.01). It also means that a diamond weighing 0.995
carat can legally be described and sold as a one-carat
diamond in the United States.
In many major diamond-trading countries and international
industry organizations, a diamond's weight can only
be rounded up to the next higher hundredth from nine
thousandths of a carat. Following this convention, a
stone which weighs 1.768 carats would be rounded to
1.76 carats; but one which weighs 1.769 carats would
be rounded to 1.77 carats. Since many of the Quality
Analysis Reports prepared by GIA!s Gem Trade Laboratories
are used internationally, the labs follow international
practice.
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