Priya Nair
Why the Mark Matters
In the UK, any gold item weighing over one gram must be hallmarked by an assay office. This isn’t just a decorative stamp; it’s a legal guarantee of purity. The term “karat” — usually spelled “carat” in British English — tells you how many parts of pure gold are mixed with other metals. So 24 karat is 99.9% gold, while 9 karat is 37.5%. Understanding these marks helps you buy with confidence, whether you’re browsing a vintage shop or a high street jeweller. The title of this guide uses the American spelling “karat”, but on UK pieces you’ll most often see “carat” or a three‑digit fineness number.
Reading a UK Hallmark
A UK hallmark typically carries three compulsory marks: the sponsor’s mark (the maker or importer), the assay office mark, and the fineness mark. The assay office marks are London (leopard’s head), Birmingham (anchor), Sheffield (rose), and Edinburgh (castle). The fineness mark is a number: 375 for 9ct, 585 for 14ct, 750 for 18ct, 916 for 22ct, and 999 for 24ct. You may also see a date letter, which is optional but often included. Some pieces carry a traditional carat mark such as “9ct” or “18ct” alongside the number. If you spot “karat” spelled with a K, it’s likely an imported piece or American terminology — still useful, but always check for a UK assay office mark if you want that legal assurance.
What the Common Carats Mean
Here’s how the most common ratings translate into practical wear:
- 9ct (375): 37.5% gold. Hardwearing, affordable, and popular for everyday rings and chains. The colour can be a paler yellow because there’s less pure gold.
- 14ct (585): 58.5% gold. A good middle ground, common in imported jewellery. More durable than 18ct, with a richer colour than 9ct.
- 18ct (750): 75% gold. The standard for fine British jewellery. Rich yellow colour, a lovely balance of luxury and strength. Softer than 9ct but still suitable for daily wear.
- 22ct (916): 91.6% gold. Deep yellow, traditional for Asian bridal jewellery. Too soft for everyday rings; prone to scratching and bending.
- 24ct (999): 99.9% gold. Pure gold, usually reserved for investment coins or ceremonial pieces. Extremely soft and not practical for most jewellery.
How Alloys Change Colour and Durability
Pure gold is too soft for most jewellery, so it’s alloyed with metals such as copper, silver, zinc, palladium, and nickel. The mix determines both colour and hardness. Yellow gold uses copper and silver in varying ratios. Rose gold gets its warm pink hue from a higher copper content. White gold relies on palladium or nickel, often plated with rhodium for a bright white finish. The higher the carat, the more gold and the softer the metal. That’s why 9ct is the hardest — it contains more alloy. 18ct strikes a beautiful balance. 22ct and 24ct scratch easily, so they’re best for special occasions or investment. White gold plating can wear off over time, requiring re‑plating every year or two.
Practical Tips for Buying and Wearing
When buying, use a jeweller’s loupe to check the hallmark. Look for the fineness number and the assay office mark. If a piece is unmarked or the mark is worn away, be cautious. For everyday wear, 9ct or 18ct are sensible choices. 18ct is ideal for heirloom pieces that will be passed down. Clean your gold with warm soapy water and a soft brush; avoid harsh chemicals. Store pieces separately to prevent scratches. If you have white gold, ask your jeweller about rhodium plating. And remember that “carat” for gold is different from “carat” for gemstones, which measures weight. The mark is your guarantee, so take a moment to read it — it tells you exactly what you’re wearing.
