Gold Carats, Colours and Hallmarks, Explained
What 750 and 585 mean, why white gold is often plated and how rose gold gets its blush.
Inside almost every gold ring there is a tiny number, and it tells a long story. It reveals how much pure gold the alloy contains, how hard the metal will be and how it will wear, while the marks beside it record who made the piece and, in some countries, who tested it. Here is how carats, colours and hallmarks work, in plain language, from 999 down to 375.
Parts of Twenty-Four
Gold purity is measured in carats, on a scale of twenty-four parts. Pure gold is 24 carat. An 18 carat alloy contains eighteen parts gold and six parts other metals, which means 75 per cent gold. This carat of purity is not the carat used to weigh gemstones, which is a unit of mass; the two simply share a name.
Most jewellery is stamped not in carats but with a millesimal number, meaning parts per thousand. That number is what you will usually find inside a band, on the back of a pendant or beside the clasp of a chain.
- 24 carat: 999, or 99.9 per cent gold
- 22 carat: 916, or 91.6 per cent
- 18 carat: 750, or 75 per cent
- 14 carat: 585, or 58.5 per cent
- 9 carat: 375, or 37.5 per cent
Purity and Strength
Pure gold is gloriously soft. It bends, scratches and dents easily, which is why it is almost always alloyed for jewellery. The higher the carat, the richer and more intense the yellow and the softer the metal; the lower the carat, the paler the tone and the harder the alloy.
For rings and bracelets that meet the world every day, 18 and 14 carat offer the happiest balance. Eighteen carat keeps a deep, warm glow and enough strength to hold fine settings; fourteen carat is tougher still and wonderfully practical. Twenty-two and twenty-four carat suit pieces that lead a gentler life, such as earrings, pendants and ceremonial jewellery.
Where Colour Comes From
Gold itself has one colour. Every other shade comes from the metals it is alloyed with. Classic yellow gold balances silver and copper, so that neither pulls the tone too far. Add more copper and the gold warms into rose; add more still and it deepens to red, the shade of late autumn light.
White gold is made by alloying gold with palladium or other white metals, which soften its natural yellow. Most white gold jewellery is then finished with a thin layer of rhodium, a bright white metal of the platinum family, which gives it a cool, mirror-like brilliance. That plating is renewed over the years, usually when a faint warmth begins to show where the piece meets the skin most often.
Two neighbouring metals often join the conversation. Platinum is usually stamped 950, meaning 95 per cent platinum, and is naturally white without any plating. Sterling silver is stamped 925, for 92.5 per cent silver, with the remainder usually copper.
Marks of Trust
A hallmark is a small archive in metal. It usually combines a fineness mark, which states the purity, with a maker's or sponsor's mark that identifies who made or submitted the piece. In some countries, the United Kingdom among them, further marks are compulsory and are applied by an independent assay office once the metal has been tested.
The British tradition is among the oldest anywhere. It dates back to a statute of 1300, and the word hallmark itself comes from Goldsmiths' Hall in London, where pieces were brought to be assayed and marked. A British hallmark still carries the symbol of the assay office that tested it, such as the leopard's head of London.
Other countries follow other customs. In Germany, for example, the maker stamps the fineness under their own responsibility. Both approaches rest on the same principle: a number you can read and a name that stands behind it.
A hallmark is a promise made small enough to fit inside a ring.
Caring for Each Colour
Each colour asks for slightly different care. Yellow and rose gold need little more than warm water, a drop of mild soap and a soft brush, followed by a gentle dry with a lint-free cloth. Rose gold is robust, thanks to its copper. White gold enjoys an occasional visit to a goldsmith to have its rhodium renewed, which restores its first brightness.
All gold, whatever its carat, is happiest stored separately in soft pouches or a lined box, since harder stones and metals can scratch it. Take rings off before the swimming pool, as chlorine is unkind to alloys, and before working with your hands. High carat pieces, being the softest, deserve the most tenderness.
Once you can read them, those tiny numbers make every piece more legible. A 750 inside a ring is a statement of proportion, a rose blush a quiet note about copper, a hallmark a promise seven centuries in the making. Knowing what they mean changes nothing about how a jewel looks, only how well you understand what you are wearing.
Questions, answered
What does 750 mean on gold jewellery?
It means the alloy contains 750 parts of pure gold per thousand, or 75 per cent, which is 18 carat. The remaining quarter consists of other metals, such as silver, copper or palladium, which give the gold its colour and its strength.
Why does white gold turn slightly yellow?
White gold is an alloy of gold with white metals, and it usually receives a thin rhodium plating for extra brightness. Over the years that plating wears at the points of most contact, revealing the gentle warmth of the alloy beneath. A goldsmith can renew the rhodium and restore the cool white finish.
Is 9 carat gold real gold?
Yes. Nine carat gold contains 37.5 per cent pure gold, stamped 375, alloyed with other metals that make it hard-wearing and lighter in tone. It is a recognised standard in the United Kingdom and elsewhere, and it is appreciated for its durability in everyday jewellery.
Three terms
- Millesimal fineness
- A measure of purity in parts per thousand, so that 750 means 750 parts of pure gold.
- Rhodium plating
- A thin coating of rhodium, a bright white metal of the platinum group, applied to white gold.
- Assay office
- An independent institution that tests the purity of precious metals and applies official hallmarks.
Photo: licensed stock photography.
