Tag Archives: hallmark



A pearl which has only been partly drilled, as for rings or stud earrings. These sell for more than those which are fully drilled. The best have a flawless domed side.


The term hallmark is often confused with branding, but it is not a branding. Hallmarking is a specific process of assaying precious metals and marking them as having passed a required standard. It is a guarantee of quality of content. Hallmarking dates, in England, from 1300 when Edward 1 brought in a requirement for standardisation of silver for coin and wrought pieces, which were to be marked with the leopard’s head mark to show they had passed assay. Variations on the leopard’s head are still used today for sterling silver pieces marked at the London assay office, run by the Worshipful Company of Goldsmiths. Different marks are used to denote fine silver, and the various grades of gold, plus platinum and palladium. A mark will show when and in which office the item was assayed, plus what metal and who made the item. The mark is either struck to the metal (the origin of ‘making one’s mark’ as the maker can optionally still strike their own sponsor’s mark before assay or the mark can be struck by laser. All Pearlescence precious metals over the required minimum weight carries the London Assay office hallmark of owner Wendy Graham (Initials wmg in an oval cartouche).


Pearls are harvested when the pearl farmer judges that there is enough nacre. This can either be cyclical or annual depending on the weather and the mollusc – in China the traditional harvests are in the winter as it is thought that winter nacre on the outside means a sharper and more intense lustre.

The harvest is also a time to seed the new crop, as the mantle tissue from the best producing pearls will be used to start the pearls for the next crop.

While some farms (eg Cortez and the Kamoka Tahitian pearl farm) market their own pearls as a name and brand in its own right, most pearls worldwide go into processing to be mixed with others to make strands at the processing factories. Some pearl sellers will claim that all their pearls come from the farm they visited, but this is extremely unlikely as one farm will not produce enough pearls to produce a range for retail.(and it is unlikely that a pearl farm will be able to drill and match for strands)

Tahitian pearl harvest.

Hyriopsis cumingi

The triangle shell is the shell used to culture most freshwater pearls in China

Irradiation Irradiation has differing effects from freshwater to salt water cultured pearls. The gamma rays do not affect the nacre layers of a salt water cultured pearl, but in fact darken the nucleus of the pearl. An irradiated salt water pearl appears to be grey or blue. The nacre of freshwater irradiated pearls, on the other hand, if affected by the gamma rays and can become very dark. Some of these freshwater treated pearls will also have an intense metallic sheen and iridescent orient over their surface.


Behind securely closed doors: The London Assay Office

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.

Hall of The Worshipful Company of Goldsmiths

Hall of The Worshipful Company of Goldsmiths

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

ceiling in main hall

The sumptuous ceiling in the main hall

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.

Modern Hallmarking

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)

hallmarking room.

This is the main hallmarking room. Very skilled

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

Hallmark being applied with a laser

Hallmark being applied with a laser

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!

certificate assay tour

Pearlescence got a certificate!