Metal fineness explained

When it comes to precious metals, terms like sterling silver and eighteen karat gold are all expressions we know well, but what do they actually mean when it comes to the fineness of the metal?  We know that gold is more expensive than silver, and the higher the karat of the gold, the higher the price, but why is that?

Silver fineness

A hugely popular and affordable metal, practically every civilisation has used silver. As quite a malleable metal, the purest silver is softer than both platinum and gold. For this very 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%.

Gold fineness

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 - equal to 100% pure gold
  • 22 karat - made up of 22 parts gold and 2 parts alloy resulting in 91.7% pure gold
  • 18 karat - made up of 18 parts gold and 6 parts alloy resulting in 75% pure gold
  • 14 karat - made up of 14 parts gold and 10 parts alloy resulting in 58.3% pure gold
  • 9 karat - made up of 9 parts gold and 15 parts alloy resulting in 37.5% pure gold

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