First introduced in the 14th century by King Edward I to combat rogue goldsmiths selling underweight or fake gold and silver, the role of the Assay Office represents one of the earliest forms of consumer regulation and protection. In its infancy, a group of trusted assayers would travel to perform the task of verifying precious metals, and would “mark” them to confirm quality and purity. Over time, the travelling became impractical and items were brought to Goldsmiths’ Hall for testing and marking- hence the evolution of the term “hallmarking”.
The term “assay” is derived from the French word “essai”, which means “trial” or “test”. In the context of hallmarking, assaying is the method of analysing the composition of metal, and there are a number of different techniques- both ancient and modern. These include:
- Cupellation- this process is 2,000 years old and is a refining process which involves extracting the pure gold portion from the base metals in an alloy to calculate the overall percentage of gold content. It involves taking a physical sample for testing (usually a fine scraping) so is slightly destructive, but is very accurate.
- Touchstone and testing needles- this ancient method employs the use of a small dark tablet of finely grained material (such as bassonite). A testing needle (which has been subjected to cupellation, so is a reliable reference point) tipped with metal of a known concentration is drawn across the surface to leave a line of residue. The process is repeated with the item being tested, so it is also slightly destructive. The colours of the two lines were compared with a well trained eye to determine the fineness of the metal. However, in modern times the residues are also subjected to acid (usually nitric acid or aqua regia). Gold is largely unaffected by most acids, the but alloys will generally react with the acid and disappear, leaving a gold residue which allows identification. This process is the origin for the expression “Coming up to scratch”!
This is an example of a touchstone and needles:
- XRF- The vast majority of items tested nowadays are assayed using x-ray fluorescence. This is a fast, non destructive diagnostic test which exposes articles to x-rays and records the fluorescent responses and compares them with known responses of various metals to determine the content and concentration of various metals present in an object. The Assay Office is rightly proud of the role they play in consumer protection.
Understanding the marks
By law, jewellery composed of precious metal in excess of a certain weight must be independently hallmarked. This is your assurance that the jewellery has been checked and confirms the purity.
Each piece assayed will be stamped with a number of marks:
- one which represents the office which carried out the test (the London Assay Office is a leopard’s head);
- the fineness mark to confirm the type of precious metal and its purity;
- a date letter which confirms which year a piece was marked; and
- the sponsor’s mark. This confirms who made the piece.
Every piece of jewellery sold by Jacqui Larsson Fine Jewellery proudly bears this sponsor’s mark: