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A Guide to Measures for Gold and Silver Purity

One of the most important considerations when investing in gold or silver is the purity of the metal you’re buying. Due to gold and silver being relatively soft metals, they are normally mixed with other metals to make them harder. Just a small difference in purity can have a massive impact on the overall value of the goods so It’s important to understand what the different figures used for measuring purity mean.

Millesimal Fineness

The purity of gold and silver bars/coins is normally referred to as “the millesimal fineness”. This measures the overall purity of precious metals based on parts per thousand. For example, if a gold bar has a fineness of 999 then it is made up of 999 parts gold to 1-part other metals. Because no form of gold available on the market is 100% pure, the purest gold bullion bars and coins, normally have a millesimal fineness of 999 or 999.9. The finer the purity of the metal, the higher its value.

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Measuring the purity of silver

Like gold, silver is often measured using millesimal fineness, with the purest form of silver measuring .999. When investing in silver, however, you may come across terms such as “Sterling silver or “Britannia silver”. These hallmarks are direct references to the metal’s purity and can be found stamped on the metal itself. Both Britannia silver and Sterling silver is slightly less pure than fine silver with Britannia silver measuring 95.8 and sterling silver 92.5 on the millesimal fineness scale. Some silver bars are made in Sterling silver as are certain collectables and antiques. Britannia silver was a standard first introduced by the 1696 Coinage Act. No coins are currently minted in Britannia Silver, the last being the 2012 edition Silver Britannia.

Gold and Silver purity measures
999.9 fine gold bars


When buying gold or silver in various forms, you will sometimes PHYS01_Animated_Gif_2_MPUfind that its purity is measured in “karats”. Gold jewellery, for example, is often measured in karats. The purest form of gold is 24 karats; however, it only needs to have a millesimal fineness of 990 to obtain this status. The reason why karats are not used to measure the purity of gold and silver bullion is that they are not a fine enough measure, however, you can work out the “fineness” of precious metals measured by dividing the karat by 24 and multiplying the value by 1000. For example, a 12-karat gold necklace has a purity of 50% – 12 divided by 24 x 1000. Different countries also have different rules on the minimum purity levels required for gold and silver. Therefore, when trading in gold and silver abroad, you should be aware that what classifies as 24/18 karat gold in one country might not necessarily be the same in the UK.

Verifying the purity of precious metals

Currently, there are only two-real methods of verifying the marked fineness of precious metals and one of these methods requires destroying it completely in order to separate the different metals within it. This is known as assaying the metal. The other method uses x-ray fluorescence to determine the metal content. However, this method isn’t 100% accurate as it only measures the outermost section of the metal and therefore might get fooled by thick plating. Due to the difficulty in being able to determine the true purity of precious metals, it is always advised that you buy gold or silver from a reputable broker or dealer so as you can be assured that you’re getting what you’re paying for.

Gold and Silver purity measures
999.9 silver Queen’s Beasts coin

Invest in gold & silver through physical gold

If you’re looking to invest in gold or silver, then the best way to do so is by purchasing bullion. Bullion is the highest purity form of gold and silver and can be purchased in the form of bars (such as our 1KG silver bar) or bullion coins. Here at Physical Gold, we stock a wide range of gold and silver bullion including legal tender coins produced by the Royal Mint and gold bars in various sizes including 1oz, 100g right up to 1kilo bars. For more information on measures for gold and silver purity or to ask our advisers any questions on the best way to invest, please give us call on 020 7060 9992.

Image Credits: Hamilton Leen and Eric Golub

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