A small number engraved on the inside of a ring or on the clasp of a necklace is a fineness hallmark. It tells you how much of the piece of jewellery consists of pure precious metal, expressed as a number of parts per thousand. If it says 585, then 585 out of 1000 parts are pure gold - that is, 58.5 percent. The most common numbers on Danish jewellery are 585 and 750 on gold and 925 on silver, and they all say the same thing: how pure the metal is.

Pure gold is too soft for jewellery that is to be worn daily, so it is mixed with other metals such as copper, silver and zinc. The mixture is called an alloy, and the number states exactly how much pure gold the alloy contains. The higher the number, the more pure metal.

Gold hallmarks from 333 to 999 and what they correspond to in karat

On gold the number is usually one of five levels. 333 means 33.3 percent pure gold, 375 means 37.5 percent, 585 means 58.5 percent, 750 means 75 percent, and 999 is almost pure gold. Each number corresponds to a karat value, which is the old way of indicating the purity of gold.

Here karat is written with a k, because it concerns the fineness of the gold - not carat with a c, which is the unit of weight for diamonds. 8 karat corresponds to 333, 9 karat to 375, 14 karat to 585, 18 karat to 750 and 24 karat to pure gold. 14 karat and 18 karat are the two most widely used for finer jewellery, because they strike a balance between a high gold content and a hardness that withstands daily use.

Longvé's gold jewellery is made in 14K gold, where the number 585 is stamped into the metal itself. This gives a solid gold content combined with a durability suited to rings, necklaces and earrings you wear every day.

Does the hallmark on white gold mean something different than on gold?

White gold has the same fineness hallmark as gold - a white gold ring in 14 karat is also stamped 585. The number only tells you how much pure gold the alloy contains, not what colour it has.

The difference lies in what the gold is mixed with. White gold is alloyed with white metals such as palladium, so the colour becomes cool and silver-like instead of yellow. Pure gold is always yellow, regardless of whether it ends up as gold or white gold, and that is why the gold content - and thus the hallmark - is the same in both. If you want to see the difference between the two in practice, you can compare gold and white gold side by side.

What do 925 and the other numbers on silver mean?

On silver the most frequent number is 925. It means that the piece of jewellery consists of 92.5 percent pure silver, and the metal is therefore called sterling silver. The remaining 7.5 percent is typically copper, which makes the silver harder and more durable, since pure silver is too soft for jewellery.

You may also come across 800 and 830 on older silver, which indicate 80 and 83 percent pure silver respectively. 925 is, however, the international standard for finer silver jewellery today. At Longvé, sterling silver is used for, among other things, signet rings, where the number 925 is stamped into the ring.

Where is the hallmark located on a piece of jewellery?

The hallmark is always placed in a discreet spot where it does not disturb the design. On a ring it sits on the inside of the ring band. On a necklace or a bracelet you will usually find it on the clasp or on a small plate close to the clasp, and on earrings it sits on the post or the hook.

The number is often very small and can be difficult to read with the naked eye. A loupe or a good magnifying glass makes it easier to read, and on some jewellery the fineness number appears together with a maker's or guarantee mark from the manufacturer.

Other numbers you may encounter in jewellery

In addition to the fineness hallmark, a piece of jewellery may carry other numbers that mean something entirely different. On a ring a number such as 54 or 56 often indicates the ring size - that is, the ring's inner circumference in millimetres - and not the purity of the metal.

On diamond jewellery you may also see a carat indication, here with a c, which is the weight of the stone. 1 carat equals 0.2 grams, so a diamond of 0.50 carat weighs a tenth of a gram. That indication has nothing to do with the fineness of the gold, even though both numbers can appear on the same piece of jewellery. Longvé carries both natural diamonds and lab-grown diamonds, where the carat weight is stated in the product's name.

Why is the number worth knowing?

The hallmark is your assurance that the piece of jewellery is what it claims to be. A gold piece without a fineness hallmark may be rolled gold or gold-plated, where only a thin layer of gold lies over another metal, and here the number is missing precisely because it is not solid precious metal all the way through.

When you know the number, you can tell for yourself whether a ring is 14 karat or 18 karat, and whether a necklace is sterling silver or a lower silver alloy. This makes it easier to compare pieces of jewellery and to know how they should be cared for, since different alloys tolerate different treatment.