Argentium® Silver is a patented and trademarked alloy that is at least 92.5% pure silver, just like traditional sterling. What makes it different from traditional sterling silver is that a small amount of germanium replaces some of the copper that is usually the other 7.5% of sterling silver. Peter Johns, a professor of silversmithing at Middlesex University in England, invented Argentium® Silver in 1996.
• is highly tarnish-resistant.
• has greater ductility and malleability than traditional sterling.
• can be precipitation-hardened using a kitchen oven.
• can be fused and welded.
• does not firescale.
Despite its many advantages, working with Argentium® Silver is not very different from working with traditional sterling. It is useful, though, to know as much as possible about the differences.
Differentiating Argentium® Silver from Traditional Sterling Silver
At this time, there is no foolproof way for a metalsmith without access to analysis equipment to figure out whether a piece of metal is traditional sterling or Argentium® Silver, so it is important to be organized if you have both Argentium® Silver and traditional sterling in your studio.
If I find myself needing to distinguish between then, my preferred method is to:
1) Abrade the surface of the metal—with a Scotch-Brite™ wheel, for instance—to remove any grease, dirt, germanium oxide or fine silver.
2) Heat it lightly with a torch, moving the flame on and off the metal, so that it is exposed to oxygen. Argentium will usually stay silvery; traditional sterling usually darkens. Ideally, when you do this, you do it alongside a piece of metal that you know is Argentium® Silver as well as a piece that you know is traditional sterling, for comparison. It is best if all the silver samples have been cleaned and treated the same way and have the same surface finish.
3) If the silver darkens, keep heating lightly, moving the torch on and off the metal. Argentium® will lighten in color as the germanium grabs the oxygen from the copper (traditional sterling will darken further).
What is Germanium?
Germanium (Ge) is an element, named for its discovery in Germany in 1886. Its atomic number is 32, its atomic weight is 72.64 and it is located below silicon on the periodic table. It is chemically similar to tin. Germanium is not found as a free element in nature. Germanium is found in zinc ores, coal, germanite and argyrodite. In researching this article, I have been intrigued to see that germanium is not listed in charts comparing metals and their characteristics in any of the jewelry or silversmithing books in my studio. Germanium is a metalloid, as are silicon, manganese, boron and sulfur. These elements are on the border between the metallic elements of the periodic table and the non-metallic elements. Metalloids have both metallic and non-metallic properties. Metalloids tend to be semiconductors rather than conductors. Germanium is a semiconductor, with electrical properties between those of a metal and an insulator. (Conduction: the result of collisions between molecules; when one end of an object is heated, the molecules vibrate faster and the energy is transferred to their neighbors.7 ) Because germanium is less conductive than many other metals, Argentium® Silver can be fused and welded more easily. Pure germanium is crystalline, gray and lustrous. It is very brittle; it shatters easily with a hammer. Interestingly, it seems to have a bleaching characteristic when alloyed— alloys made with it look more white and less yellow.
What is Firescale? Why Doesn’t Argentium® Silver Get It?
When heated, traditional sterling forms cuprous oxide (Cu2O), known as firescale or firestain, that annoying purplish layer that lurks under the surface of traditional sterling after annealing or soldering. Firescale needs to be removed via abrasives or chemicals, covered with electroplating or covered by depleting the copper from the surface through repeated heating and pickling (often called “bringing up the fine silver” or depletion gilding). Though Argentium® Silver may oxidize when heated, the oxide is cupric oxide (CuO). This is a surface oxide that pickle removes completely; there is no underlying cuprous oxide firescale. An unusual property of the element silver (Ag) is that it allows oxygen to penetrate through its surface, and into the interior of the metal. That is why the Cu2O/firescale is able to form under the surface of traditional sterling . The addition of germanium to the sterling silver alloy stops the penetration of oxygen past the surface.