The quickest way to tell whether a piece of jewellery is real gold is to look for the hallmark on the inside or near the clasp. If it reads 585, 750, 333 or 999, the number tells you how large a proportion of pure gold the piece contains. A hallmark alone is not a guarantee, however, which is why there are several simple tests you can do at home - as well as one reliable method that requires a professional.

Gold is a precious metal that does not react with air or water and therefore does not rust or tarnish. Most home tests rely precisely on this property: they reveal whether something behaves like gold or like a base metal that is only gold-plated. Below, the methods are reviewed from the easiest to the most precise.

What does the hallmark on a gold piece mean?

Genuine gold jewellery is hallmarked with a number that indicates the fineness - that is, how many thousandths of the alloy are pure gold. Pure gold is too soft for everyday use, so it is mixed with other metals to provide strength and durability.

The most common gold hallmarks are:

In Denmark, 585, that is 14 carat, is the most widespread. Longvé's jewellery is made precisely in 14K gold and 14K white gold, which strikes a good balance between gold content and wear resistance.

The hallmark is often placed in a discreet spot: on the inside of a ring band, near the clasp of a necklace or bracelet, or on the post behind an earring. The numbers are small, so a loupe and good light make them easier to read. If the hallmark is missing entirely, it does not necessarily mean the piece is fake - older or handmade jewellery may be unmarked - but it is a reason to test further.

Does a magnet work on gold?

Gold is not magnetic. If you hold a strong magnet up to a piece of jewellery and it is pulled towards the magnet, there is base metal inside - typically iron or nickel beneath a thin layer of gold.

The test is quick and harmless, but it has a clear limitation. Several of the metals used to counterfeit gold are also non-magnetic, for example brass or certain types of stainless steel. A piece that does not react to the magnet is therefore not automatically genuine - it has merely passed the first, crudest check. If it does react, however, you can be almost certain that it is not solid gold.

How do you perform an acid test on gold?

The acid test is the most widespread home method, because it can distinguish between different finenesses. You can buy kits with acid bottles calibrated to each gold carat, along with a small scratching plate of black stone.

You rub the piece against the plate so that a thin streak of metal is deposited, and then drop a drop of the acid that corresponds to the presumed fineness. If the streak remains without changing, the gold matches the stated carat. If the streak disappears or discolours, the fineness is lower than assumed, or it is not gold at all.

The acid test requires caution: the acid is corrosive, and the test leaves a small mark on the piece. It also only reveals the surface, so a heavily gold-plated item can deceive you if you do not scratch deeply enough. If you are unsure about the handling, it is better to let a goldsmith take care of it.

Can you recognise real gold by its weight?

Gold is one of the heaviest metals you encounter in jewellery. Its density is markedly higher than that of the base metals most often used for counterfeits, and you can exploit this with a simple weight test at home.

The method is based on measuring the weight of the piece and then how much water it displaces in a measuring beaker. The weight divided by the amount of displaced water gives the density, which for pure gold is around 19.3 grams per cubic centimetre. The lower the fineness, the lower the density, because the mixed-in metals are lighter.

The test is imprecise for small pieces, where measurement inaccuracy carries a lot of weight, and it cannot finely distinguish between two neighbouring carats. But if a piece feels strikingly light in the hand relative to its size, it is a sign that there is not much gold in it.

How do you test gold with ceramic?

A quick check involves drawing the piece across an untreated ceramic surface, for example the underside of a shard of kitchen tile. Genuine gold leaves a golden streak, while gold-plated or base metal typically leaves a grey or black streak.

The test scratches the piece slightly and should only be used in a spot that is not visible. It gives an indication, not a definitive answer, and it says nothing about the fineness. It works best as a supplement to the hallmark and magnet, when you want to form an overall impression.

When should you have gold assessed by a goldsmith?

The home tests can together make you reasonably certain, but the only method that gives a precise and gentle answer is a professional assessment. A goldsmith can use an XRF device that measures the exact metal composition without scratching or damaging the piece, and can at the same time read hallmarks and any maker's marks correctly.

A professional assessment is especially relevant if the piece is inherited or bought second-hand without a clear hallmark, if the home tests give conflicting results, or if the piece has sentimental value that you do not want to risk damaging with acid or scratches.

If you are buying new, on the other hand, you can trust the hallmark. New jewellery from an established retailer is hallmarked according to the rules, so the fineness is shown directly - this applies to both gold and white gold. At Longvé, the entire range is gathered under gold and white gold, and if you want to see how 14K gold looks across jewellery types, necklaces and rings give a good overview.

What about white gold?

White gold is genuine gold, but mixed with white metals such as palladium, so the colour becomes cool instead of golden. It has the same fineness as gold - 14 carat white gold is therefore also hallmarked 585 - and is tested in the same way with hallmark, magnet and weight.

Confusion most often occurs with silver, because the colours resemble each other. Here the hallmark helps: silver is typically hallmarked 925 for sterling silver, while white gold bears the fineness number of gold. If you are unsure what white gold actually is, and how it differs from other white metals, the article what is white gold explores the topic in more detail.

Many gold pieces bear several hallmarks alongside the fineness number - a responsibility mark or maker's mark that shows who is behind the piece. If you want to understand the background of the numbers and the other marks, you can read more in what does 925 mean in a ring.