What the 250 parts that are not gold decide

Pure gold is 24 carat, soft enough to mark with a fingernail and too soft for a ring that is worn. Everything sold as jewelry is therefore an alloy, and the alloy is where all of the interesting behaviour lives. The carat number tells you how much gold is present. It tells you nothing about the three quarters of the question that decides how the piece will look in a decade.

The carats, in parts per thousand

• 24 carat: 999 gold. Deep yellow, very soft, used for investment and for some Asian bridal jewelry.
• 22 carat: 916. Rich colour, still soft, traditional across South Asia and the Middle East.
• 18 carat: 750. The standard for fine jewelry in Europe. Enough gold for colour and value, enough alloy for durability.
• 14 carat: 585. Harder, paler, more scratch resistant, the American mainstream.
• 9 carat: 375. Legal to call gold in the United Kingdom and several other markets, more than half other metals, and it tarnishes.

Yellow, rose, white

In 18 carat, the 250 parts of alloy decide the colour. Roughly equal silver and copper gives standard yellow. More copper, typically 200 parts copper to 50 silver, gives rose, and the more copper the pinker and the harder the metal. Palladium, silver and sometimes nickel give white, which is not actually white: raw white gold alloy is a pale grey with a faint yellow or brownish cast.

So white gold is plated. A micron or two of rhodium, a platinum group metal that is brilliantly white and very hard, is electroplated over the surface. It looks superb and it is a coating, which means it wears. On a ring worn daily, the plating thins on the underside of the band within eighteen months to three years and the warm grey underneath begins to show through. Replating costs 40 to 90 and is a maintenance item forever.

White gold is a yellow metal wearing white paint. The paint is excellent, and it is still paint.

Platinum, and the honest comparison

Platinum in jewelry is usually 950 parts per thousand, so it is purer than 18 carat gold and genuinely white all the way through. It is denser, so the same ring is noticeably heavier. It is softer at the surface, which means it scratches more readily, but it does not lose metal the way gold does: a scratch in platinum displaces metal into a ridge rather than removing it, which is why platinum develops a patina and gold slowly gets thinner.

That last point matters over decades. An 18 carat band worn for thirty years is measurably thinner than it was. A platinum band of the same age has the same metal, redistributed, and can be polished back. Platinum costs more to buy and more to work, and it never needs plating. Over a long life it is often the cheaper metal.

The skin question

Almost all jewelry allergy is nickel allergy, and it is common. The European nickel directive limits release from anything in prolonged skin contact, which is why a ring bought in the EU is rarely the culprit and one bought elsewhere sometimes is. Palladium white gold is the nickel free alternative and is more expensive. Rose gold is high in copper, which can leave a faint green mark on some skin in humid weather, a harmless reaction between copper and skin acids.

If a ring has never caused a problem and suddenly does, the usual explanation is that the rhodium plating has worn through and the nickel bearing alloy underneath is now in contact with skin. Replating fixes it.

Reading the stamps

Look inside the band. A number is a fineness mark: 750, 585, 375, 950 for platinum, 925 for sterling silver. Additional marks vary by country and can identify the assay office, the maker and the year. A piece with no mark at all is not automatically fake, since worn or resized bands lose their stamps, but it does mean the fineness is unverified and a jeweller test costs almost nothing.

The word gold in a description, with no number, means nothing. Gold plated is a microscopic layer, gold filled is a mechanically bonded layer of a defined thickness and considerably better, and vermeil is gold over sterling silver with a minimum thickness in some markets and no minimum in others.

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