How to know the carat of your gold jewellery

The price of your gold jewellery is determined based on the quality of the gold. We then distinguish different carats ranging from 24 to 9. The minimum gold purity standard authorised in France is 37.5% pure gold, that is to say that the jewel must be at least composed of 37.5% gold in the alloy, or 375 thousandths, in other words, 9 carat.

Recognise the purity of gold with hallmarks

There are different techniques to know the purity of gold. One of them is to identify the hallmarks.

So, if your gold jewellery is marked:

– A seahorse: then you are in the presence of a 24 carat jewel (pure gold)

– An eagle’s head or an owl: then you are in the presence of a jewel of 18 carats (18/24 or 750 thousandths)

– A scallop shell: then the equivalence will be 14 carats (14/24 or 585 thousandths)

– A clover: in this case, you will be in the presence of a jewel of 9 carats (9/24 or 375 thousandths)

If you notice one of these hallmarks on your gold jewellery, then you can know its purity in gold.

Recognise the purity of gold with professional tools

There are three different professional methods used to determine the purity of gold. The first is the touchstone. The technique is simple and fast, because it allows to know precisely the gold content. This method also allows not to damage the jewel to know its purity because the sample is very low. It consists of rubbing the metal on a black touchstone, leaving a small trace and then applying a drop of acid. Depending on the acid used and the chemical reaction, we can determine the purity of your gold jewellery.

The method of verification by cupellation makes it possible to determine the exact content of silver or gold in a jewel. This is one of the oldest and most accurate methods for determining the gold content in a jewel. The method involves melting a sample in a porous dish to remove base metals. Interestingly, gold and silver are two materials which are not absorbed by the dish. The final weight divided by the initial weight gives the gold and silver content. To determine the exact gold content, without the silver, the sample is boiled in nitric acid until all the silver is converted to silver nitrate. The weight of the remaining sample, which is pure gold, divided by the initial weight, gives the gold content of the original sample. It is of course necessary to have very precise scales; they measure samples to the nearest ten thousandth of a gram!

Finally, the last method is the test by XRF spectrometry and X-rays. It is fast and does not damage the jewel, but the machine is worth more than €15,000 and is not on every street corner! At Osprey Paris we have a spectrometer in our store located at 278 rue Saint-Honoré, Paris for instant analysis of your objects. With this method, you can also know the other components of your jewel.

You now know the different ways to know more or less precisely the purity of your gold jewellery. If you have any doubts with the data from the professional methods, you can complete your verification with the identification of the hallmark of your jewel. We have a whole chapter on hallmarks, see at the top of the web page.

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