The Karatage System For Gold Jewelry
Gold jewelry is usually described in terms of karatage, which is an indication of its gold content, for example 18 karat or 18K. Alternatively, the gold content can be described in terms of ‘fineness’, which is the gold content expressed in parts per thousand, for example 750 (which is 18 carat or 75.0% gold).
Since the price paid by the purchaser for gold jewelry is based on the amount of gold in it, it is important for the consumer to know how many karats of gold there is in the piece. Most jewelry worldwide is marked with the karatage or fineness. This may be part of a Hallmark on the jewelry .
Pure gold (‘fine gold’) is 24 karats and so 24 carats is theoretically 100% gold. In Chinese, it is also known as “Chuk Kam”, meaning ‘pure gold’ and is defined as 99.0% gold minimum. Thus, there is a 1.0% negative tolerance allowed in this case.
The karatage System
Any caratage value lower than 24 is a measure of how much gold there is in the jewelry gold alloy. Thus 18 ct is 18/24ths of 100% gold = 75.0% gold. In fineness terms, this is described as 750 fineness, i.e. 750 parts of gold per thousand parts. This is not always exactly the mathematical value! For example, 22 karat is mathematically 22/24ths x 100 = 91.666% but the accepted international standard is 91.60%
Many countries only allow certain karatages of gold jewelry to be sold. For example, in the United Kingdom, one can make and sell 9, 14 ,18 and 22 carat gold jewelry but not 12 carat gold as the latter is not a recognised karatage standard by law. In some countries, jewelry lower than 12 carats (50% gold or 500 fineness) cannot be described as gold.
The advantage of making jewelry in karatages lower than 24 kt, apart from price, is the wide range of colour that can be achieved, from socalled green, pale yellow, yellow, rose/pink to red as well as white, depending on the balance of other alloying metals used. The lower the karatage, the wider range of color is possible . Additionally, properties such as strength and hardness are improved over pure gold, leading to improved wear and scratch resistance and less liable to distortion and damage.
The karatages of jewelry allowed by law varies from country to country. In the U.S., for example, the following karatages are allowed: 10, 14 (585), 18 (750), 22 (916), and 24 (990 and 999). In many countries, a large range of karatages is legally allowed but only a few are in common use.