The London Assay office, where much of the gold, silver, platinum and palladium sold in the UK is hallmarked, lives on the third floor of the hall or headquarters of the Worshipful Company of Goldsmiths, a stone’s throw from St Paul’s Cathedral in the City of London.
I was fortunate to be one of the lucky few gold and silversmiths to be included in a party allowed in for a day to see the processes involved.
Hallmarking is the the oldest form of consumer protection in the UK, with Goldsmith’s Guild getting its first royal charter from Edward III in 1327 (the guild HQ has been on the same site since 1339) . Now the guild, through the London Assay Office, is one of four independent
organisations (also Birmingham, Sheffield and Edinburgh) which assay precious metals as required by the 1973 Hallmarking Act.
A hallmark is NOT a trademark. A hallmark is punched or lasered into the metal after the metal content is analysed and it is confirmed to be of a certain standard. Each hallmark tells you who made the piece or sent it for assay (the sponsor’s mark – Pearlescence’s is WMG in a cartouche shape) what quality of what metal both in traditional and millesimal (figures) marks, which assay office and in what year.
The Assay office also conducts an annual examination of the coins manufactured by the Royal Mint (known as the Trial of the Pyx) and uses its huge collection of old silver items as a resource for the dating of suspect antiques. Two years ago the head of assay personally checked and hallmarked every gold and silver medal for the London Olympics.
It seems astonishing that every item sent in for assay is individually checked…but it is. A method dating back to Roman times, touch testing is the quickest and simplest. Pearlescence’s silver ring was checked in a demonstration (no photos by me, unfortunately due to obvious security needs). In a method which ancient Romans and Egyptians would recognise and still be able to carry out, the piece is simply rubbed onto a highly polished tile of lydite until a 1cm by 2mm ish streak is made. Compare that with the streak made by a touch needle of known quality. check by a drop of acid on both. If they match you have identified the metal and its quality (in this case Sterling 925 silver)
The second ancient method is cupellation (which is a splendid word) and this method dates back to pre-Roman times. It is the most accurate. The gold sample is weighed very accurately then a known amount of silver is added in a process called inquartation. this mix is wrapped in lead foil and shaped into a ball, which is placed in a cupel. the cupel is put into a furnace for 20 minutes and everything melts. everything except the pure gold and silver is absorbed into the cupel. Dissolve the silver in acid (parting) Weigh the remaining pure gold, subtract the known amount of silver and simple maths then gives the proportion of gold in the assay item. (accurate to one part per thousand)
Finally there is the ultra modern x-ray fluorescence where an item is placed into a machine and bombarded with x-rays. The resulting spectrum identifies the metal and carat. Pearlescence tried this with some unknown gold made into a fused ring (9ct) and another ring made of silver wire and fused gold (interestingly the silver only came up to 800 proof with a lot of gold mixed in (so will be marked as silver), while the gold was over 18ct)
Once the items have passed assay they will be hallmarked. This, astonishingly, is still mostly done by hand. we had a go. It’s scary to try to put the London mark onto metal properly and cleanly. The brilliant folk in the photo above do it so well that even with the smallest punch you can still count the (three each side on the leopard’s face) vibrissae.
Alternately marks can be applied with a laser now or mechanically with a press for long runs of identical items
Top tip from the day – heartfelt plea from the assayers and markers…please do not pack each item into its own packet. We have instantly resolved to use those plastic compartment trays. Make your assayer love you!
An amazing day, I learned so much. And I even got a certificate!