If you own a piece of gold, silver, platinum or palladium jewellery purchased in the UK or even some silverware like an antique silver knife, fork or spoon, you may have noticed three or four small stamps discretely hammered into the surface of the metal. This is a hallmark.
Well before I studied gemmology and jewellery in more detail I was fascinated by hallmarks. How do you decipher them and what can they tell us?
Over the centuries, many kingdoms and countries have used marks on precious metals to verify their metal content, especially gold, but few have been as assiduous as England and the United Kingdom more widely.
To hall mark
The control of precious metals like gold and silver were critical to maintaining a stable economy and society. When money was literally worth its weight in gold (or silver) there needed to be some way of telling a vendor that your money was as good as it looked. Fraud and gold in particularly have never been far apart. By the mid-13th century, medieval English King Henry III attempted to compel certain goldsmiths of the City of London to oversee the purity of gold in circulation.
By 1300, the first assay office was established in London at Goldsmith’s Hall under statute of King Edward I and run by goldsmiths called ‘guardians of the craft’. London Assay Office continues to exist to this day and keeps the leopard’s head as its symbol.
To hallmark literally meant that an item of precious metal has been taken to the Goldsmith’s Hall (now known as an assay office) for testing to obtain its purity mark. Now it is a guarantee of quality and makes transactions involving hallmarked items much safer for willing buyers and sellers.
Today it remains a legal requirement in the UK for all gold, silver, platinum and palladium items over a certain weight to be hallmarked before it is described or sold. The Hallmarking Act 1973 came into force in 1975 and now governs the law around assaying and hallmarking precious metals. This Act applies across England, Northern Ireland, Scotland and Wales.
Many other countries have their own assaying and hallmarking laws and conventions, but it is by no means a worldwide phenomenon, for example, the USA has no federal or independent hallmarking system, nor a legal requirement for gold or silver to be hallmarked.
The crown and anchor
One story that always comes up when talking about the assay offices of the UK is how they came to adopt their assay office mark also known as a town mark (from a time when there were many more assay offices than the four in operation today: Birmingham, London, Sheffield, Edinburgh).
Birmingham Assay Office was established in 1773 by Act of Parliament, alongside Sheffield Assay Office. Matthew Boulton, the Birmingham industrialist who was involved in everything from steam engines to buttons was instrumental in getting an assay office set up near to the heart / heat of industry in Britain at the time.
It was at the behest not of goldsmiths or gold dealers but silversmiths in both Birmingham and Sheffield. It is said that a group of them got together at a pub in London called the Crown and Anchor. When it came to deciding on their symbols they tossed a coin: one would adopt the crown and the other, the anchor. Birmingham got the anchor and Sheffield the crown. After 1975 Sheffield abandoned its crown in favour of the White Rose (Tudor rose) for its town mark. The crown mark was also variously used to denote 18k and 22k gold fineness in other English assay offices so it has at least stopped confusion for items hallmarked in the last 50 years. The Sheffield crown in any case is of slightly different shape to the fineness mark for gold.
Hallmarking and jewellery standards today
In May 2024 I attended a fantastic introduction to UK hallmarking delivered by Marie Brennan, Commercial Manager of Birmingham Assay Office. Birmingham Assay Office regularly runs introductory sessions both to UK Hallmarking and the services they offer at their offices and laboratories in Birmingham–which extend well beyond hallmarking. Check out their website to see what education and training is on offer.
I jumped then at the opportunity to attend a half day Valuer’s Experience Day at Birmingham Assay Office in July 2026. This was organised in collaboration with the National Association of Jewellers Institute of Registered Valuers with whom I am currently working through the JET Foundations of Appraisal Practice course.
How does an assay office work? Who uses them? What else do they do? What kind of skills do you need to work there?
The UK has one of the tightest and best standards for jewellery and other items made of precious metals, as we have seen with the provisions of the Hallmarking Act 1973. The four assay offices in the UK are independent of government and provide the services needed to assay (test) and hallmark precious metals. Jewellery makers, retailers and silversmiths can register themselves with an assay office of their choice and you might see that their marks, officially known as a sponsor’s mark, appears next to the hallmark. Each office keeps a register of all these marks, historic and current.
Situated in the heart of Birmingham’s Jewellery Quarter, we were welcomed into a meeting room surrounded by interesting artefacts relating to the assay office’s history. After an introduction to Birmingham Assay Office and its history and services by Marie Brennan we were taken to the space where the precious metals are tested. Incidentally, Birmingham offers elemental testing not just for gold and precious metals but also of other kinds of thing made of metals such as electrical components. Lily Walker also accompanied our visit.
XRF (X-Ray Fluorescence) machines are used in the assay process these days which allows for non-destructive testing and the determination of the metal’s fineness. Fineness refers to the quantity of gold in the alloy, so for example, 9k (9 carat) gold is 375 parts per 1000 pure gold so you will see the number 375 in the hallmark. 18k gold is 750 parts per 1000 pure gold so you will see the number 750. Fineness marks have changed over the last century so you might also see the number 18 for 18k or the number 14 for 14k.
A crown is used to denote gold, a lion for sterling silver (925), the figure of Britannia for Britannia silver–a purer form of silver–(958), a crown for gold, an orb for platinum and a helmeted head (Pallas) for palladium. You will see all these fineness marks and their explanations in jewellers shops and UK-based online jewellery sellers because it is a legal requirement to do so.
Traditional acid-based or even electrical testing of metals requires a small amount of filing to ensure you are not just testing a plating. Some of the valuers at Birmingham still swear by acid testing in their work. Acid is going to reveal the quantity of alloy with the gold (gold will not react to the acid used) so for example the quantity of copper in the metal will react and turn the metal a different colour from which you then judge its fineness e.g. 9k, 18k.
Birmingham receives hundreds if not thousands of items to test per week. Huge retailers, TV shopping channels to independent jewellers use the office.
After assaying, the item moves to hallmarking. Both punch marks and laser hallmarking, in addition to laser hallmarks in relief, are offered at Birmingham. I was captivated by observing the women and men stamping hallmarks by hand especially on the very tiniest of clasps on fine chains. The speed, concentration and precision on show were impressive.
In addition to the sponsor’s mark (not formally part of a hallmark), fineness symbols and marks and assay office or town mark, you may also see an alphabet letter. This is the date letter. Do not be confused by this being the date of manufacture or making of the item of jewellery, it’s the date the item was assayed and there can often be a big difference in the two if an item was hallmarked long after it was made, for example, to sell on. I have seen some beautiful historic pieces inconsiderately hallmarked for this purpose but in actual fact this does not need to happen as jewellery made before 1950 is exempt from the legal requirements of hallmarking.
Date marks for silver and gold were different until 1975 and since 1999 date marks are an optional component of the hallmark except if you have your item hallmarked at the London Assay Office who will add it regardless. The progress of the alphabet alters by capitalisation, font and the shape of the cartouche or frame it is in with every iteration. This makes it possible to reference each letter to a year of assay.
There are some international conventions for hallmarking that may result in a Common Control Mark (CCM) or Convention mark to be added. You will see the symbol of scales and then a number for fineness. This kind of mark is common to those countries who have signed up to various conventions on the standards of precious metals so they can move across borders more easily.
There are rules too about the hallmarking of items that are plated or have interlayers. Base metals plated with precious metals e.g. gold-plated brass cannot be hallmarked. Gold plated silver will be marked as silver. Plating must not be more than 2 microns thick if the item is to be hallmarked after plating. This is because the testing involved needs to be able to penetrate that far to verify the precious metal contents of the item. Base metal interlayers that are used commonly elsewhere, such as silver plated nickel, are not permitted in the UK and will not be hallmarked. This is because of their potential hazard to those who have allergies. Assaying, therefore, can also provide a useful service in ensuring items of jewellery are safe to wear.
Birmingham Assay Office will also assay and mark mixed metal objects so long as they are clearly distinguishable by colour or metal. +METAL is a mark you may see when an item that has hallmarkable precious metal (not less than 100 microns) mixed with base metal alongside (it has to be visible not an interlayer). Only the precious metal component is hallmarked.
Other marks have come and gone, such as ceremonial marks to mark a coronation or jubilee, foreign import marks and duty marks.
Watching the laser hallmarking process in action was very compelling. It’s so precise and you can get marks onto the most discrete of places on a piece of jewellery or a silver picture frame for example. As jewellery becomes more physically complex because of CAD-based designs laser hallmarking will become ever more vital.
We then got to have a go at making a punch mark of the Birmingham anchor. The deft of hand you need for a firm tap of the hammer to get an even mark is much more difficult than it may seem. We all took it in turns. I don’t think I will be getting a job as a hallmark any time soon but it was thrilling to see the tradition of using a hammer and punch still in action in a modern setting.
More than hallmarking
Birmingham Assay Office offers 360-degree services used regularly by jewellery professionals and others in allied industries. Beyond hallmarking, the office offers analytical and chemical testing for jewellery particularly for hazardous substances such as nickel, lead and cadmium. This includes hypoallergenic testing too, something that is very important when jewellery enters UK circulation from many parts of the world which do not maintain the same standards as us.
In addition to the elemental testing (what is this made of?) already mentioned and the education and training on offer–Birmingham City University’s jewellery and gemmology courses are taught here too–Birmingham Assay Office offers jewellery and watch valuation services which benefits from a fully-kitted gemmological lab that includes diamond screening (to identify synthetic vs natural diamonds), diamond colour treatments, coloured gemstone identification and coloured gemstone treatments and pearl testing including x-rays to determine natural and cultured origins. This is part of the AnchorCert suite of products Birmingham Assay Office offers the industry.
Demonstrating the diamond screening machine which uses deep UV (shorter wavelengths than SWUV of ~225nm) I was quite happy to see that my little diamond barley twist ring was full of tiny melee natural diamonds and no synthetics or simulants had snuck in. I also really enjoyed hearing about the Raman spectrometer. Theirs is as big as a room but you have the ability to use liquid nitrogen to ‘still’ the atoms in a stone so you can get a really sharp spectrum giving you the most accurate results for what compositional and trace elements are contained in a gemstone. None of this would be possible with just the analytical machines as it requires specialist skills and experience to operate them and interpret the results. As well as those who work the XRF machines during the assaying process, Birmingham employs lab gemmologists who undertake the mounted and unmounted gem testing work.
It was, of course, a delight to speak to two valuers who provide Birmingham Assay Office’s Jewellery Valuation Service. Like most jewellery valuers they receive the whole spectrum of items to value, from church monstrances to the latest Rolex. They also authenticate handbags and trainers! Given you could have some analytical work done on your gems or jewellery at the same time as a valuation, they offer a very compelling service. Indeed many independent jewellery valuers use Birmingham’s gemmological and valuation services in their own practices. Finally there is a co-working space with access to basic tools and materials and desk-space called the Assay Hub. If you were a Birmingham-based valuer or even one that had a big job on and you just needed that extra assistance of not just space, tools and services, but also colleagues, hiring a desk at Assay Hub would be very tempting.
The Valuers Experience Day at Birmingham Assay Office opened my eyes to the kind of things we can do here in the UK when it comes to gems and jewellery, that, when you get taught on gemmological courses at both Gem-A and GIA, you are perhaps not fully aware of. It sometimes feels like all the action takes place in Switzerland, California or Bangkok but here in the UK we have Birmingham Assay Office where you can get all sorts of things analysed, authenticated, and researched. So much more than hallmarks.
References
Sheffield Assay Office, Bradbury’s Book of Hallmarks. New edition 2023.
Ian Pickford (ed.), Jackson’s Hallmarks. 2nd Edition 2016.