Inside the London Assay Office: What Hallmarks Mean on Your Bespoke Jewellery

Every piece of bespoke jewellery made at Hatton Garden Bespoke Jewellery is hallmarked at the London Assay Office, a short walk from our workshop at The Goldsmiths' Centre. This guide explains what the hallmark is, why it matters, and how to read the marks stamped inside your ring.

What is hallmarking, and why does it matter?

In the UK, hallmarking is a legal requirement for most precious-metal jewellery. Any item of gold, silver, platinum, or palladium above a certain weight must carry a hallmark certifying the metal's purity. It is a 700-year-old consumer protection: you cannot legally sell an “18ct gold” ring in the UK unless an independent Assay Office has tested the metal and stamped it accordingly.

The hallmark is the one piece of certification on your ring that is not marketing. It is an independently-verified legal guarantee that the metal is what your jeweller said it is.

The Goldsmiths' Company Assay Office London

London has had an Assay Office since 1478. The modern Goldsmiths' Company Assay Office, the one that marks our pieces, sits at Goldsmiths' Hall on Gutter Lane, a short walk from Hatton Garden. It is one of four Assay Offices in the UK; the others are Birmingham, Sheffield, and Edinburgh. Each has its own “town mark” (see below).

We chose London both for proximity (pieces are hand-delivered and collected) and because the London leopard's head is the most-recognised hallmark in the UK jewellery trade.

The four marks you'll find on your ring

A complete modern UK hallmark consists of four compulsory marks, struck side-by-side inside the band. Here's what each one means.

1. The sponsor's mark (maker's mark)

A unique set of initials inside a cartouche, registered to the workshop that made the piece. Our sponsor mark identifies us as the sponsor and maker of record, so if a repair or resize is ever needed, any competent jeweller in the UK trade can trace the piece back to our workshop.

2. The standard mark (fineness)

A three-digit number showing the precious metal content in parts per thousand. You will see:

• 750 for 18ct gold (75.0% pure)
• 585 for 14ct gold (58.5% pure)
• 375 for 9ct gold (37.5% pure)
• 950 for platinum (95.0% pure)
• 925 for sterling silver

For a guide to choosing between 9ct and 18ct, and between gold and platinum, see our metals guide.

3. The assay office mark

A pictorial mark identifying which Assay Office tested the piece:

• Leopard's head, London
• Anchor, Birmingham
• Rose, Sheffield
• Castle, Edinburgh

Every piece we make carries the London leopard.

4. The date letter

A single letter in a shield showing the year the piece was assayed. The alphabet cycles through 25 years, with each 25-year cycle using a different font style and shield shape. The date letter is not legally compulsory but is almost always struck, it is useful for dating pieces later in life.

Are there pieces that don't need hallmarking?

Yes. The UK hallmarking weight thresholds are:

• Gold, under 1 gram
• Silver, under 7.78 grams
• Platinum, under 0.5 grams
• Palladium, under 1 gram

Most engagement rings exceed these weights easily (a plain 2mm 18ct gold band is around 3g; a solitaire setting plus band weighs 4 to 6g), so hallmarking is near-universal for the pieces we make. Very delicate earrings or pendants occasionally fall under the threshold.

Why hallmarking is included in our pricing

Some jewellers treat hallmarking as a separate line item, a £30 to £50 add-on at the end of the quote. We do not. Every bespoke piece we make at The Goldsmiths' Centre is sent for London hallmarking as part of the quoted price, and the three-to-four-week lead time we quote you already includes the trip to the Assay Office and back.

It is a small thing, but it reflects the way we think about the craft: the hallmark is the final signature on your piece and it deserves to be treated as part of the making, not as an administrative afterthought.

Reading the hallmark on a family piece

If you have inherited a piece of jewellery and you want to know when it was made, the hallmark is usually the fastest route. Bring it in during your consultation, we will read the marks with you, identify the Assay Office, the metal, and (from the date letter) the decade. It is often the most interesting part of the consultation for clients who are redesigning around a family stone.

Frequently asked questions

Where is the hallmark on my ring?
Usually inside the band, on the underside opposite the setting. Small pieces sometimes have the hallmark laser-etched rather than punched, but the content is identical.

Is a hallmark the same as a diamond certificate?
No. The hallmark certifies the metal only. The diamond is certified separately, with us, GIA or IGI certification is available on every centre stone. Read more about our diamonds here.

Can hallmarks be faked?
It is a criminal offence in the UK. All Assay Offices use punches that are physically held on site, and modern hallmarks often include microscopic elements that cannot be replicated with workshop equipment.

Will my engraved names be on the same side as the hallmark?
Usually not, engraving goes on the inside of the band opposite the hallmark, so both are legible. Discuss placement at the CAD stage and we will map it out.

Book a consultation at our Hatton Garden studio to discuss your commission. We typically reply within four working hours.