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Gold Purity

Gold Alloys

In ancient times gold was used as it was mined, however today gold is refined to produce the highest purity and level of fineness. The fineness level is the proportion of pure precious metal in an alloy. Due to gold being very soft other metals are introduced to make it a stronger and add colour, these metals are known as ‘the alloys’. White and rose gold are produced by adding other metals; for example copper can be used to create a rosy red or pink gold.

The difference in colour can be seen in some Victorian rings which were made from British gold sovereign coins, (which were 22 carat gold) copper was the sole alloy metal which resulted in a red colour. In the Victorian era it was common for the Father of the bride to give a sovereign as material for the ring to be made.

Gold is measured as parts per 1000 in fineness and this tells us their degree of purity is known as a carat (ct) or Karat (k) i.e. 9ct, 14ct etc. This is the amount of gold within a metal and tells us how pure it is and possible value. Higher carat items will be tougher and are more resistant to chemicals. For example, 18ct alloys are almost totally resistant to chemical attack where as 9ct alloys can turn dull or even completely tarnish from exposure.

The alloys used by jewellers are of standardised purity and these can be recognized differently in different countries. The 6 we have in the UK are as follows:

  • 999 - 990 - 24 carat gold or "pure gold" - gold content: 99%+
  • 916 - 22 carat gold - gold content: 91.6%
  • 750 - 18 carat gold - gold content: 75%
  • 625 - 15 carat gold - gold content: 62.5% (popular in antique jewellery)
  • 585 - 14 carat gold - gold content: 58.5%
  • 375 - 9 carat gold - gold content: 37.5%

This is tested in an assay office after an item has been manufactured. Once it has passed the independent test it is then stamped with the hallmark to declare the level of purity. In doing this it means it is to a specified legal standard.

Antique items of jewellery will often not be hallmarked. Pieces may not originally have been hallmarked, or overtime they will wear and become illegible. If this is the case, at AC Silver our items are tested using a Niton XL2 Analyzer.

Find out more about hallmarking antique jewellery here.

Fineness Associated With Platinum

There are four recognised standards of platinum:

  • 850 (platinum content: 85%)
  • 900 (platinum content: 90% )
  • 950 most common purity used for platinum jewellery (platinum content: 95%)
  • 999 considered 100% pure platinum used in bars and coins (platinum content: 99.9%)

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International Federation of Art and Antique Dealer Associations CINOA
National Association of Jewellery UK's trade association NAJ