When it comes to precious metals, terms like sterling silver, 9k gold and 18K gold are all expressions we know well but what do they actually mean when it comes to the fineness of the metal? We also know that gold is more expensive than silver and the higher K of the gold the higher the price. This is why.
A hugely popular and affordable metal, practically every civilisation has used silver. It’s quite a malleable metal and the purest silver is softer than both platinum and gold. For this reason it’s typically alloyed with a secondary metal to add strength, with copper being a common choice. The purity of silver is expressed as ‘parts per thousand’ so in the case of 925 Sterling Silver, which is 92.5% pure, for every 1000 parts 75 or 7.5% is an alloy. Another popular purity is 958 which means that the metal is 95.8% pure silver and the alloy content 4.2%.
The most popular precious metal of them all, gold boasts an intrinsic value. Mined from copper ores and the earth’s crust, South Africa is the world’s leading producer of gold. The prices of gold are, as you would expect, based on both its purity and its weight. Amazingly strong and malleable, pure gold will never corrode or tarnish and whilst around 75% of gold produced is
used in the jewellery industry pure gold is simply too soft for most applications. The result of this is that gold has to be alloyed with other metals in order to improve the durability.
The international standard of the fineness of gold is the karat, commonly abbreviated to just a K. The gold content of any item is expressed as a 24 part ratio, thus pure gold is 24K. The most common purities of gold are;
- 24 karat – 100% pure gold
- 22K – 22 parts gold and 2 parts alloy makes 22 karat 91.7% pure gold
- 18K – 18 part gold and 6 part alloy makes 18 karat 75% pure gold
- 14K – 14 part gold and 10 part alloy makes 14 karat 58.3% pure gold
- 9K – 9 part gold and 15 part alloy makes 9 karat 37.5% pure gold