Carats and Karats
The term carat is used as both a unit of mass — especially for gemstones — and as a measure of purity for gold. In the United States and Canada these terms are spelt differently — as carat and karat respectively — to avoid confusion. But many people get them confused anyway.
The term carat originates from the Greek keration for “fruit of the carob”. Carob seeds were used for precision weighing of gold and gemstones, since it was thought that carob seeds had a uniform weight. The modern carat, known as the metric carat, was adopted in 1907, defined as a weight of 200 mg. This is actually very close to the mass of larger carob seeds. One carat can be divided into 100 points, a measurement often used in the diamond trade.
Interestingly, the term karat also derives from the name of the carob seed. So how did they get from the weight of the carob seed to the purity of gold? And why is pure gold defined as “24 karat”? A precise answer is not easy to find, but the connection appears to derive from the Roman Emperor Constantine, who introduced a gold coin that weighed exactly 24 carob seeds.
Under the karat system of fineness of gold, pure gold is 24 karat or 24k, 18k is 75% pure and 12k gold is 50% pure. This system is gradually giving way to the millesimal finess system which expresses purity in terms of parts per thousands of the alloy. Thus 22k gold is marked as “916” under this system, or 91.6% gold. It is certainly a simpler and less confusing method.
Therefore a Carat (Ct or ct) is a weight measurement in reference to precious gemstones such as Diamonds, Sapphires, Rubies and depending on where you are in the world a Carat may also be used in place of the term karat. However the term karat is never used in regards to gemstones.
A karat (K or k) is the measurement of the purity of gold. Gold itself is very soft, and like silver, it needs to be alloyed with other metals to make it stronger and less expensive. 24 karat gold is considered pure gold, or 100% gold.
While many people think 24 karat gold is the best quality you can buy, the soft metal is less durable and it can scratch or damage easily. To prevent this, gold is alloyed with metals such as silver, copper and zinc. When producing white gold alloys, nickel, copper and zinc are used. So, the karat is measured by the ratio of gold to the alloyed metal.
18 karat ( .750) contains 75% pure gold.
14 karat ( .585) contains 58.5% pure gold.
10 karat ( .417) contains 41.7% pure gold.
9 karat (.375) contains 37.5% pure gold.
10k 14k and 18k are standards used in the U.S.
9k and 18k are standards used in the UK and Europe
1 karat of gold = 1000/24. So 9 karat is 37.5% gold. Divide the carat of gold you have by 24 and the result is the percentage.
9k 9/24 37.5%
10k 10/24 41.67%
14k 14/24 58.33%
18k 18/24 75.00%
The remaining percentage of the metals are based on the type of gold you have:
Yellow Gold – Copper, Silver
Rose, Red and Pink Gold – Copper, Silver
White Gold – Nickel, Zinc, Copper
Green Gold – Silver, Zinc, Copper