Hallmarks have historically been applied to precious metals as a guarantee of a certain degree of purity or fineness of the metal. Hallmarks vary in appearance depending on the country in which they were applied. For example, in some countries the hallmark consists of several elements whilst in others, it is a single mark augmented by another. Hallmarks are typically applied to gold, silver and platinum worldwide and to palladium in some countries. The hallmarking system protects investors from buying metal collectibles that have had their precious metal content reduced by unscrupulous sellers. Therefore you can expect to find hallmarks on coins, jewelry, metallic art and any other metal item valuable enough to draw interest as an investment vehicle.
To determine the degree of purity or fineness, precious metal is subjected to formal metal testing, commonly known as assaying. The institutions that test the purity of the metal are known as assay offices. It is these offices that are responsible for applying the hallmarks nowadays. There are various methods of assay, the main ones being touchstone, x-ray fluorescence and fire assay. Touchstone consists of making a rubbing of the metal object on a special stone, treating it with acids and comparing the resultant colour to references. As the process doesn’t involve any scraping, cutting or drilling, it is particularly suitable for testing extremely valuable pieces. Another non-destructive technique, x-ray fluorescence is also quick and accurate. It not only measures the amount of the relevant precious metal present in the object but also the content of other alloying metals present. Fire assay is by far the most elaborate method and is highly destructive. The object is melted, allowing the alloys to be separated and the constituents weighed. As the process destroys the article, it is usually used to test a random sampling from one lot of items produced by the same manufacturer, such as gold rings.
These main methods of assay are used for testing finished goods. There are separate assay methods for raw materials that are yet to be touched by artistic craftsmanship. Raw silver is assayed by titration, which is a laboratory method of quantitative analysis. Gold is assayed by the metallurgical process of cupellation, in which the ore or alloy is treated under high temperatures and the noble metal is then separated from the base metals. Platinum is assayed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). ICP-AES is an analytical technique that detects metals by using inductively coupled plasma in the production of excited atoms and ions emitting electromagnetic radiation at wavelengths characteristic of a particular metal.
Once the metal article has been assayed, it’s ready to be hallmarked. There are a number of ways in which a hallmark can be struck. They include punching and laser marking, with the latter being the newer technique of the two. Steel punches are used for punching and are available in different sizes, making it possible to punch anything, from the tiniest earring to the largest silver tray. Punches are also available in either straight shank or ring shank. The former is used for normal punching with a hammer, while the latter is used to mark rings, in conjunction with a press. The problem with the punching process is that fragile items and hollowware are at risk of being damaged or distorted, which is where laser marking comes in.
Laser marking is guaranteed to leave even the most delicate article intact and works by using high power lasers to evaporate material from the object’s surface. There are currently two methods of laser marking, namely 2D and 3D. 2D laser marking works by burning the hallmark’s outline into the item, while 3D effectively simulates the marks produced by the punching technique. Some assay offices also use their laser marking technology to personalize jewelry by laser engraving. Although laser marking is fast becoming the prevalent marking technique, traditional punches are still used in some assay offices for particularly big or awkwardly shaped items.
Hallmarking is a fascinating topic and process and will continue to be so as new techniques and methods are uncovered and experimented with. As long as precious metals, and items made from these metals, are with us, then so will hallmarking and all that it entails.