The purity of gold is measured in 4 main standards, 9 carat, 10 carat, 14 carat and 18 carat gold. However, here in the UK the main two standards are 9 carat and 18 carat gold. Pure gold is known as 24 carat gold & is 100%. This is rarely used in jewellery due to how soft the pure metal is, which is why the 4 other standards are more common in jewellery around the world. Therefore, they mix the pure gold at different percentages with different alloys to create a harder, more practical metal.
The percentages are as follows:
- 9 carat gold = 37.5%
- 10 carat gold = 41.7%
- 14 carat gold = 58.5%
- 18 carat gold = 75.0%
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The remainder of the alloy is mixed with other base and precious metals, what they are mixed with is all dependant on what the final colour is to be. For example, if you are wishing to create white gold, you would mix the 37.5% of pure gold with other metals such as palladium, a naturally white metal. Rose gold you would mix copper with the alloy.
Your hallmark is your guarantee! Without a hallmark you cannot guarantee what a metal is, sometimes items will just be stamped. If your item has ‘750’ stamped on the inside this would indicate 18 carat, although this is not a full hallmark.
A full hallmark always consists of:
– A sponsors/maker’s mark, this is the mark of the registered company that submitted the item of jewellery to be hallmarked.
– A fineness mark, this mark denotes the content of precious metals within the item of jewellery.
– An assay office mark, there are only four current assay offices in the UK, each of them represented by a different symbol. (Other assay offices used to exist but have since closed, therefore other marks on older items of jewellery do exist.)
Additional marks include:
– Letter Date Marks – These marks became optional in 1999, therefore newer items may not have these marks.
– Traditional Fineness Marks – Alongside the compulsory fineness mark, you may also see a traditional mark however these are optional everywhere other than London Assay Office.
– Commemorative Marks – These hallmarks are applied to articles to commemorate landmark national events.
– Convention Marks – This is an international convention to provide a safeguard for the trade of jewellery across borders by hallmarking internationally recognised ‘control marks’ which are shown below.