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9ct vs 18ct Gold: Colour, Durability, Hallmarks and Which to Choose

“Nobody needs to feel guilty about 9ct. It's real gold with a real hallmark, and it's built for real life. Spend on 18ct when you want that warm glow, not because someone at a counter has made 9ct sound like an apology.”Her take

What's the actual difference?

A carat measures how much of an alloy is pure gold, out of 24 parts. So 9ct has 9 parts gold in 24, or 37.5%, and 18ct has 18 parts in 24, or 75%. The rest is a mix of other metals such as silver, copper or zinc, which add strength and change the colour.

That mix explains almost every practical difference. It's why the two look different, why they wear differently and why they're priced differently. Neither one is fake or second-rate. They are simply different recipes, and each has jobs it's better at.

How to check it on a UK hallmark

Look for the fineness number. In the UK, 375 means 9ct gold and 750 means 18ct gold. You may also see 585 for 14ct or 916 for 22ct. A full UK hallmark includes three compulsory marks: the sponsor's mark showing who submitted the piece, the fineness mark and the assay office mark. A date letter is optional.

Gold pieces of less than one gram are exempt from compulsory hallmarking, so tiny items may not have one. On anything heavier that's sold as gold in the UK, ask to see the mark, and use a jeweller's loupe if you need to. Keep in mind that a plated piece is a different thing altogether, as a thin gold surface over another metal is not 9ct or 18ct gold.

What do they look like side by side?

18ct yellow gold has a richer, deeper, more saturated colour, because there's so much more gold in it. 9ct yellow gold is paler and a little more lemony, and many people like that softer look. Rose and white gold differ too, so look at them together in daylight rather than under a shop's spotlights.

Think about what you already own. If you're adding to a stack, buy the same carat and colour where you can, because a pale 9ct band next to a rich 18ct ring can be noticeable. If you want them to look deliberately mixed, separate them with a plain silver or white-gold ring, or wear them on different fingers.

Which is better for everyday wear?

You'll often hear that 9ct is harder, so it must last longer. It isn't that simple. Hardness depends on the exact alloy and how the piece was made, published figures conflict, and jewellers themselves disagree about which wears better over decades. 9ct does hold up well enough to be a popular choice for daily chains, signet rings and bracelets, and its appeal is that you get more metal for the money. It's not indestructible, however, and everything scratches eventually.

The clearer difference is tarnish. With more of the other metals in it, 9ct is more likely to dull or discolour, especially around perfume, hairspray and chlorine, though a gentle clean usually brings it back. 18ct resists this better and can last for decades with sensible care. Thicker, well-made pieces hold up better than very thin ones of any carat. Two pieces rubbing together wear each other down, so a stone-set ring next to a soft band needs a jeweller's check over time. Also, check how solid the chain or clasp is: construction matters as much as the carat.

Which is better for sensitive skin?

18ct contains less of the other metals, so some people with sensitive skin find it easier to wear. But it's not automatically nickel-free, and 9ct is not automatically a problem, because the composition varies. The metals in the mix matter more than the number alone.

If you've reacted to metal jewellery before, ask the jeweller what the alloy contains before you buy, especially with white gold, which may contain nickel. Ask about their returns policy on worn items too. If your skin is sore or persistently irritated, stop wearing the piece and speak to a pharmacist or GP.

Which should you buy?

Choose by the piece and how it will be worn. Compare the price per gram when you're shopping as well as the final ticket, since a very light 18ct piece may look more delicate and be less sturdy than a heavier 9ct one at the same total cost.

• Everyday chain or bracelet: 9ct for value and a heavier feel for the money, or 18ct if you want a deeper colour and less tarnish and don't mind the cost.
• Engagement or wedding ring: either. Many people prefer 18ct for colour, but pick a matching metal for both rings, since a mismatched pair will wear unevenly.
• Christmas or birthday gift: 9ct can give a more substantial piece for the same budget. Check the recipient's existing jewellery colour first.
• Heirloom or investment-feel gift: 18ct has more gold and a richer tone, but buy it because you love it, not as a financial plan.
• Earrings: 9ct is often plenty, since they don't get the same knocks as rings.

Questions people ask

The takeaway

9ct for the piece that lives on you, 18ct for the colour you can't stop looking at, and the hallmark to prove it either way.

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