Karat (kt) is a term used to measure the purity of gold. The karat system quantifies how much pure gold is present in an alloy out of 24 parts. For example:
- 24 karat (24kt) gold is considered 100% pure gold.
- 18 karat (18kt) gold contains 18 parts pure gold and 6 parts other metals, making it 75% gold.
- 14 karat (14kt) gold consists of 14 parts gold and 10 parts other metals, equating to 58.3% gold.
The additional metals in lower karat gold alloys (such as copper, silver, zinc, etc.) are used to enhance strength, durability, and colour variations, allowing for a broader range of gold jewellery. Pure gold (24kt) is quite soft and often not suitable for everyday wear jewellery, which is why alloys are commonly used.
In some regions, particularly in the UK and other parts of Europe and South Africa, gold purity is often marked as “9ct,” “18ct,” etc., where “ct” stands for “carat.” This can be somewhat confusing since “carat” is also widely used to denote the weight of gemstones. In the context of gold, “ct” refers to “karat” in these markings, indicating the purity of the gold.
Comparatively, carat (ct) used in gemstones is a unit of weight where one carat equals 200 milligrams or 0.2 grams. It is important to differentiate between “karat” for gold purity and “carat” for gemstone weight, as they refer to distinct aspects of jewellery valuation and characteristics.
So, when you see stamps like “9ct” or “18ct” on gold jewelry, these are referring to the karat rating of the gold, indicating the proportion of gold contained in the metal alloy. The use of “ct” in this context should not be confused with its use in gemstone weight, where it accurately measures how much a gemstone weighs.