Gold hallmarks, explained

A wedding ring in wartime

In 1942, with Britain at war and every ounce of gold accounted for, an official order restricted the making of gold wedding rings to 9 carat. Couples still married, and still exchanged rings, but the rings were paler and harder than their parents' had been, and the number inside them said so.

That number is the heart of every gold hallmark. It tells you, precisely and independently, how much of the metal is gold. Everything else in the hallmark is there to say who vouches for it and where it was tested. Once you know what the number means, the rest is easy.

What a carat is

Pure gold is beautiful and impractically soft, so jewellery gold is almost always an alloy: gold mixed with other metals such as silver, copper, zinc or palladium. The carat says how much of the alloy is gold, counted in twenty-fourths. Pure gold is 24 carat. 18 carat gold is 18 parts gold in every 24, or three quarters.

Modern hallmarks don't use carats at all. They give the gold content in parts per thousand, which is more precise and easier to compare. The two systems line up like this.

The number is a minimum, not an average. A piece marked 750 has been tested and found to contain at least 750 parts of gold in every thousand.

One word of warning: the carat used for gold has nothing to do with the carat used for diamonds and other gemstones, which is a unit of weight, a fifth of a gram. A 1 carat diamond set in 18 carat gold is using the same word for two different things.

Reading the marks

A British gold hallmark follows the same pattern as one on silver. Three marks are compulsory, and they are usually read from left to right.

• The sponsor's mark. At least two letters inside a shaped outline, registered to the person or company that sent the piece for testing.
• The fineness mark. The gold content in parts per thousand, such as 750. The shape drawn around the number tells you the metal. For gold, it is a rectangle with its corners clipped off, which is how you can tell a gold mark from a silver one at a glance.
• The assay office mark. Which office tested it: a leopard's head for London, an anchor for Birmingham, a rose for Sheffield or a castle for Edinburgh.

Then come the extras. The crown is the traditional symbol for gold, and in UK law it can go alongside any of the six gold standards, though it is entirely optional. A date letter, showing the year of marking, is optional too.

How the standards came about

British gold has been through more changes of mind than British silver. For long stretches only one standard was legal, and the numbers we use today were added one or two at a time.

The crown, then, has been on British gold for more than two centuries. It started as the mark of 18 carat and is now a choice open to every standard.

What each carat is like

There is no best carat, only a trade. The more gold in the alloy, the richer the colour and the higher the price, but also the softer the metal. The less gold, the harder and more scratch resistant the piece, and the paler it looks.

• 9 carat (375). The lowest standard that can be sold as gold in the UK. Hard wearing and the most affordable, with a paler colour.
• 14 carat (585). A middle way, and widely used in Europe and America.
• 18 carat (750). Three quarters gold, with a deeper colour. A classic choice for fine jewellery and engagement rings.
• 22 carat (916). Rich, buttery and noticeably softer. It shows scratches and dents more readily, so it suits pieces that won't take hard knocks.
• 990 and 999. Almost pure gold. Too soft for most everyday jewellery.

White, yellow and rose

A hallmark tells you how much gold is in a piece, not what colour it is. The colour comes from the other quarter, or half, or more. More copper gives rose gold its warmth. White metals such as palladium or silver turn it pale for white gold. An 18 carat white gold ring and an 18 carat yellow gold ring are both marked 750.

White gold is often finished with a thin plating of rhodium, a bright white metal from the platinum family, to make it whiter still. UK rules allow gold to be plated with rhodium, gold or platinum, so a rhodium-plated white gold ring is still hallmarked gold. Over years of wear the plating can thin, and the warmer colour of the gold underneath starts to show through. A jeweller can re-plate it.

Plated, vermeil and gold tone

This is where the hallmark earns its keep. In the UK it is an offence for a business to describe something as gold unless it has been hallmarked, or is under the exemption weight. That rule shapes how every gold-coloured piece in a shop window can be described.

• Gold plated base metal, such as gold plated brass or steel, can't be hallmarked at all. That includes "rolled gold" and "bonded gold" on base metal.
• Gold plated silver is hallmarked as silver, because silver is the precious metal it is made of. It can be described with its gold, but only in a set way: the word "gold" must be followed directly by "plated", and the word "silver" must appear, as in "18ct gold plated silver ring".
• Vermeil is a traditional name for gold plated silver. In the UK it can be used, but only alongside "gold plated" and "silver". A description such as "22ct gold vermeil ring" is not allowed, because it could be read as solid gold.
• Gold tone, "gold coloured" and similar phrases describe colour only. They are how a piece with no gold in it can be described without breaking the law.

So if a piece is described simply as "gold" and weighs a gram or more, it should carry a gold hallmark. If it doesn't, ask why.

When gold needs no hallmark

Gold pieces weighing less than 1 gram don't need a hallmark. That covers many fine chains, small studs and delicate charms. Where a piece mixes gold with base metal, the 1 gram is measured against the total metal weight, not just the gold.

Mixed precious metals have a rule of their own. If a piece contains gold and silver, the exemption weight is the one for the more precious metal, gold, measured against the weight of all the precious metal together. A piece with half a gram of gold and three grams of silver weighs three and a half grams in all, well over the gold limit, so it needs a hallmark.

Antiques have their own exemption too: gold made before 1950 can be described and sold as gold without a hallmark, provided the seller can show it is of at least the minimum standard and was made before that date.

Gold marked abroad

The UK belongs to the International Convention on Hallmarking. Gold struck with the Convention's Common Control Mark, a pair of scales, in any member country is accepted in the UK without being tested again. The Convention recognises the same six gold standards as UK law: 375, 585, 750, 916, 990 and 999.

Elsewhere, you will see other systems. In the United States, gold is usually stamped with its karat, spelled with a k, such as 10K or 14K, and federal guidance requires the karat to be stated whenever solid gold alloy is described as gold. 10 karat is not a UK standard, which is why the UK guidance notes that bonded gold of 10k can only be described as 9 carat here.

The number inside the ring

The rings of 1942 are still around, many of them still worn. Look inside one and the wartime limit is still there, struck into the gold for good. That is the quiet promise of a hallmark. Long after the receipt has gone, the ring still says exactly what it is.