What Is 18K Gold and Why Diamond Jewellery Uses It

If you have looked at diamond rings, earrings or pendants, you will have noticed that most of them say "18K" or "18kt" somewhere on the page. That is not a coincidence. 18K gold is the working standard for fine diamond jewellery, and understanding it takes about five minutes.

What does 18K actually mean?

Gold purity is measured in karats out of 24. Pure gold is 24 karat. 18K means 18 parts gold out of 24, which is 75 percent gold. The remaining 25 percent is other metals, usually copper and silver, sometimes with small amounts of palladium or zinc. On a hallmark you will see this written as 750, meaning 750 parts per thousand.

The other metals are not a flaw or a trick. They are the reason the jewellery holds its shape.

Why is pure gold not used for diamond jewellery?

Pure 24K gold is soft. You can bend a thin 24K ring with your fingers, and it scratches easily. A stone setting has to grip a diamond for years, through knocks against doorframes and daily wear, so the metal around the stone needs strength. Alloying gold with harder metals gives the prongs and bands that strength.

At 18K, gold is firm enough to hold a stone securely and still rich in colour. At 22K, the metal is softer, which is lovely for plain bangles and traditional pieces but less suited to delicate prongs holding small diamonds.

How does 18K compare with 22K and 14K?

• 22K (91.6% gold): warmer, deeper yellow and softer. Common in traditional wedding jewellery.
• 18K (75% gold): a balance of colour and strength. The usual choice for diamond and gemstone settings.
• 14K (58.5% gold): harder again and lighter in colour, often chosen for everyday durability.

If you are weighing 18K against 22K for a particular piece, our guide to 18K vs 22K gold jewellery goes through it use by use.

Does 18K gold change colour?

The colour comes from the alloy mix, not from paint or plating. Yellow 18K gold is mixed to keep a natural yellow tone. Rose gold has more copper, which gives the pink hue, and white gold is mixed with whiter metals and usually finished with a bright surface. Over time, a white gold piece can look slightly warmer as the surface wears, and a jeweller can refresh it. Yellow and rose gold do not need that treatment. You can read more in how to choose between rose, white and yellow gold.

Is 18K gold worth the price?

You pay for the gold content, the making and the stones. Because 18K has less gold by weight than 22K, a piece of the same weight contains less gold. What you gain is a metal that suits fine settings. The thing to check is not just the karat but the hallmark, the weight and how the price is broken down. How a jewellery price is calculated, step by step shows each line.

How can you confirm a piece is really 18K?

Look for the BIS hallmark. A hallmarked 18K piece carries the BIS logo, the purity mark (18K750) and a six-character HUID code. The HUID is unique to that piece and can be checked against the BIS record. Our explainer on what a HUID is and how to verify it walks you through the check.

Caring for 18K diamond jewellery

18K gold is durable, but it is not indestructible. Take rings off for heavy work, keep pieces apart in a soft pouch so they do not scratch each other, and have prongs checked from time to time. A few simple habits keep it looking new for decades.

Where to start

If you want to see 18K diamond jewellery in person, our product pages list each piece's purity and weight, and in person you can ask to see the hallmark on the piece. You can browse diamond rings or earrings, or book a visit to our Patna showroom and handle the metal yourself.