Turn over a piece of antique British jewelry and you'll often find a row of tiny stamps. They can look like a secret code, but once you know how to read them, they tell you an extraordinary amount: what the piece is made of, who made it, where it was tested, and often the exact year. British hallmarking is one of the oldest forms of consumer protection in the world, and it's one of the reasons I love buying antique jewelry in England.

What is a hallmark?

A hallmark is a set of marks struck into gold, silver or platinum after the metal has been independently tested at an official Assay Office. It guarantees that the metal is at least the purity it claims to be. A full British hallmark traditionally has four parts.

1. The maker's mark

Also called the sponsor's mark, this is usually two or three initials in a shield. It identifies the jeweler, silversmith or company that sent the piece to be hallmarked. Some makers, like Charles Horner, are well documented, so the mark can tell you a great deal about a piece's story.

2. The standard mark

This tells you the purity of the metal. On sterling silver, look for the lion passant, a walking lion. On gold, you'll see the carat in numbers, such as 18 or 9, often alongside the purity in parts per thousand: 750 for 18 karat, 585 for 14 karat and 375 for 9 karat. In Britain, 15 and 12 karat gold were also legal standards between 1854 and 1932, which is why you'll often see 15 karat in Victorian and Edwardian jewelry.

3. The Assay Office mark

This shows where the piece was tested. The most common you'll find are London's leopard's head, Birmingham's anchor, Chester's three wheatsheaves and a sword, Sheffield's crown (later a rose), Edinburgh's castle and Glasgow's tree, bird, bell and fish.

4. The date letter

Each Assay Office used a letter of the alphabet to mark the year a piece was hallmarked, changing it annually. The style of the letter and the shape of the shield around it changed with each cycle, so with a reference guide you can usually date a piece to a single year. It's how we're able to say a ring was hallmarked in Chester in 1912.

Other marks you might see

Between 1784 and 1890, a duty mark showing the sovereign's head was added to show that tax had been paid on the piece. You may also find import marks on jewelry made abroad and hallmarked in Britain. Since 1975, British hallmarks have followed a single system set by the Hallmarking Act 1973, and platinum has been hallmarked since then too.

What if there's no hallmark?

Many genuine antique pieces aren't hallmarked at all. Small or delicate items were often exempt, older marks can wear away over a century of wear, and some pieces were simply never sent for assay. When a piece isn't marked, we test the metal ourselves and say so in its description, as in "tested 9K gold".

A note on karats

In Britain, gold purity is written as "ct" for carat. In the US, we write "K" for karat, so you'll see 18K in our descriptions, while the hallmark itself will still read 18 or 18ct. They mean the same thing.

Every hallmark on our pieces is read and recorded in the description, so you'll always know exactly what you're buying. If you'd like to see the marks on a piece up close, book a video consultation and I'll show you through my loupe.

Tiffany is the founder of Mayveda, a Fellow of the Gemmological Association of Great Britain (Gem-A) and a GIA-certified diamond grader.