Everything about Carat Mass totally explained
» For other uses of the word carat, see Carat.
The
carat is a unit of
mass used for measuring
gems and
pearls. Currently a carat is defined as exactly 200
mg (0.007,055
oz, 3.086
grains). This definition, known as the
metric carat, was adopted in
1907 at the Fourth
General Conference on Weights and Measures, and soon afterwards in many countries around the world. It is universally used today. The carat is divisible into one hundred
points of two milligrams each.
For
diamonds, a
paragon is a flawless stone of at least 100 carats (20
g). The
ANSI X.12 EDI standard abbreviation for the carat is
CD.
The word came to English from French, derived from the
Greek kerátion (κεράτιον), “fruit of the
carob”, via
Arabic qīrāṭ (قيراط) and
Italian carato. The
Latin word for carat is
siliqua. In past centuries, different countries each had their own carat unit, all roughly equivalent to the mass of a carob seed. These units were often used for weighing gold.
Carob seeds were used as weights on precision scales because of their reputation for having a uniform weight. However, a
2006 study found carob seeds to have as much variation in their weights as do other seeds, though it seems that it's easier than with other seeds to recognize particularly large or small specimens and remove them. Thus, the carob seed was used as a weight not because it was naturally more uniform in weight, but because it could be more easily standardized.
Historical definitions in the United Kingdom
Board of Trade carat
In the
United Kingdom, before
1888, the
Board of Trade carat was exactly
carat.
Pound carat and ounce carat
There were also two varieties of
refiners’ carats once used in the United Kingdom — the
pound carat and the
ounce carat. The
pound troy was divisible into 24
pound carats of 240 grains troy each; the pound carat was divisible into four
pound grains of 60 grains troy each; and the pound grain was divisible into four
pound quarters of 15 grains troy each. Similarly, the
ounce troy was divisible into 24
ounce carats of 20 grains troy each; the ounce carat was divisible into four
ounce grains of 5 grains troy each; and the ounce grain was divisible into four
ounce quarters of 1¼ grains troy each.
The carat of the Romans and Greeks
The
solidus (carat) was also a Roman weight unit. There is literary evidence that the weight of 72 coins of the type called
solidus was exactly a Roman pound, and that the weight of a
solidus was 24
siliquae. The weight of a Roman pound is generally believed to have been 327.45
g or possibly up to 5
g grams less. Therefore the metric equivalent of 1
solidus was approximately 189
mg. The Greeks had a similar unit of the same value.
The carat in Byzantine Egypt
A carob based weight unit was also used in Egypt in the Byzantine and early Arab periods. In this region, glass weights were used for weighing coins. From these the weight of the Egypt carat has been reconstructed as 196
mg. This is consistent with the average weights of carob seeds in the region.
The Syrian and Arabic carat in Mohammad's time
According to literary sources, the Arabic carat was only 2% less than the Syrian carat. Based on coins and glass weights their weight was reconstructed as approximately 212
mg. This is consistent with literary information that a solidus weighed slightly less than 22 carats.
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