"Not all that shines is gold," as the popular saying goes. Indeed, some things aren't quite what they appear to be. To try to identify what is genuinely gold, rather than merely gold-plated or gold-filled, several factors should be taken into account.

1. Examine your piece, look for markings

To find the karat value, you need to check whether there is any purity indication stamped onto the piece, which should range between 9k and 24k.

The characterisation of "real gold" is therefore analysed through the proportions of gold present in your jewellery. So, according to the different gold types:

24K is gold in its purest form, rarely used in jewellery
22K is composed of 91.6% fine gold. Less common, but also permitted under Portuguese law.
19.2K tells the consumer that the piece is made up of at least 80% gold. This fineness corresponds to what is known as "Portuguese Gold".
18K is a piece where, of 24 parts, 18 are gold, making it a piece with a high gold content
14K is also common in gold jewellery and means that 14 parts of the piece's composition are gold
9K – jewellery with this amount of the precious metal can be found at more affordable prices. Ideal for those who want a variety of gold pieces to wear day to day.

However, due to wear, this may not be visible, and even fake jewellery can have stamps that appear genuine, so another test will be necessary.

2. Magnet test

As it is a non-magnetic metal, gold repels the attraction generated by magnets. So, when a magnet is brought close to the piece, if it is strongly attracted to it, then it is not gold. Although this test can help rule out some metals, a lack of reaction does not always confirm the material's authenticity, as some non-magnetic metals are used in counterfeit jewellery. In other words: passing the magnet test doesn't prove a piece is gold. Therefore, the analysis needs to be complemented with other tests.

3. Density test

There are few metals denser than gold. The density of pure 24K gold is around 19.3 g/ml, the highest value among most other metals. Measuring the density of pieces helps determine whether the gold is real. As a general rule, the higher the density, the purer the gold. However, this test is only 100% reliable with jewellery that has no gemstones or additional details made from other materials.

What are the steps?

First, weigh the gold piece.
Pour water into a container with a measuring scale, without filling it completely. Then note down the measurement (ml) shown on the container.
Drop the piece into the water and note the new measurement (ml) found.
To calculate the density of a piece, use the following formula: Density = mass/volume displacement.

A result close to 19 g/ml indicates real gold or a material of similar density. To find out whether the gold is real, it should follow the measurements below:

14K — every 12.9g to 14.6g should displace 1ml of water;
18K (yellow) — 1ml for every 15.2g up to a maximum of 15.9g;
18K (white) — 14.7g to 16.9g should displace 1ml;
22K — 17.7 to 17.8g for 1ml of displacement.

4. Ceramic test

Using a piece of unglazed ceramic tile or an unglazed ceramic plate, rub the piece against its surface. If it leaves a black mark, this indicates the piece is not gold, but if the mark is gold-coloured, then we are looking at a piece of pure gold.

Although this test is simple and accessible, it can damage the pieces, so it should not be done at home, but rather carried out by a professional from Loja do Ouro and Gold Store Premium.

5. Nitric acid test

Nitric acid is one of the most commonly used methods to determine the purity of gold, as well as silver. Real gold does not react to nitric acid.

However, due to the difficulties in acquiring the acid and the safety risks involved in the practice, it is best to leave this test to a professional from Loja do Ouro and Gold Store Premium. This acid is highly corrosive!

To test the piece, simply clean it with a soft cloth, lightly scrape the surface of the jewellery, and apply a small amount of nitric acid using a dropper. After a few minutes, a colour will appear where the drop was placed:

If it turns green, this means the piece is only gold-plated
If it turns whitish and milky, this means it is silver plated with gold
If there is no colour change, it probably means the piece is genuinely gold

A piece of gold jewellery is a significant investment, so it's important to be certain that you have an authentic piece. At Loja do Ouro and Gold Store Premium, we have Official Appraisers, Licensed by Casa da Moeda, available to assess your pieces free of charge. Visit us at one of our stores across the country, or contact us to make an appointment.

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