When you examine a gold coin, bar, or piece of jewellery, you will usually find a small stamp or engraving indicating its purity. These marks, often called hallmarks or fineness marks, tell you how much pure gold is present in the item. Understanding these numbers and letters helps you know exactly what you are buying. The two main systems used worldwide are the carat system and the millesimal fineness system.
The Carat System: 24K, 22K, 18K, and 14K
The carat (abbreviated as K or kt) measures the proportion of pure gold in an alloy. Pure gold is defined as 24 carats. This means that 24K gold is 99.9% gold, with only trace impurities. Because pure gold is very soft, it is often mixed with other metals such as copper, silver, or zinc to create a harder, more durable alloy for everyday wear.
- 24K (24 carats): Pure gold. It has a deep yellow colour and is very malleable. It is most commonly used for investment bars and coins, or for special ceremonial jewellery that is not worn daily.
- 22K (22 carats): Contains 22 parts gold and 2 parts other metals. This is 91.7% gold. 22K gold is popular for high-end jewellery, especially in South Asia and the Middle East, because it retains a rich colour while being stronger than 24K.
- 18K (18 carats): Contains 18 parts gold and 6 parts alloy, making it 75% gold. 18K is widely used in fine jewellery worldwide. It offers a good balance of purity, colour, and durability.
- 14K (14 carats): Contains 14 parts gold and 10 parts alloy, or 58.3% gold. This is common in North American and European jewellery because it is very hard and resistant to scratching.
- 10K (10 carats): The minimum legal purity for gold in many countries. It is 41.7% gold. 10K jewellery is durable and affordable but has a paler yellow colour.
To calculate the percentage of gold from a carat value, divide the carat number by 24. For example, 18K ÷ 24 = 0.75, or 75% gold.
The Millesimal Fineness System: 999, 916, 750, 585
The millesimal fineness system expresses purity in parts per thousand. This system is more precise and is used on most modern bullion bars and coins, as well as on jewellery in many countries. The common marks are:
- 999 (or 999.9): Pure gold, equivalent to 24K. A bar stamped 999 contains 999 parts gold per 1,000 parts of metal.
- 916 (or 916.7): Equivalent to 22K. This mark means the item is 91.67% gold. It is widely used on gold coins and jewellery in India and the Middle East.
- 750: Equivalent to 18K. This is a very common hallmark for high-quality European jewellery.
- 585: Equivalent to 14K. This mark is often seen on jewellery from the United States and parts of Europe.
- 375: Equivalent to 9K. This is a lower-purity gold commonly used in the United Kingdom for affordable jewellery.
When you see a three-digit number, you can read it as the percentage of gold with one decimal place. For example, 750 means 75.0% gold.
Other Marks You Might Encounter
In addition to the purity mark, many countries require additional hallmarks that indicate the assay office, the manufacturer, and the year of manufacture. For example, in the United Kingdom, a complete hallmark includes a sponsor's mark, a fineness mark, an assay office mark, and a date letter. In countries without a compulsory hallmarking system, you may see only a manufacturer's stamp or a simple fineness mark. It is always wise to buy from reputable dealers who provide independent certification for gold bars and coins.
Gold purity marks are a reliable guide, but they can be forged. If you are unsure about an item, a simple test using a gold testing kit or a visit to a professional assayer can confirm its authenticity. Understanding these marks empowers you to make informed decisions about gold items, whether for jewellery or investment.