Different Silver Alloys

One thing I am always asked is, “how is Argentium silver different from other silver alloys”? With there being so many different alloys now available I thought I would try to categorise and summarise each alloy type’s particular quirks.

Traditional sterling silver – This is the simple 92,5% silver, 7.5% copper combination. A good basic alloy with good hardness. For silversmiths the problems of firescale and tarnish are well documented.

Spinning silvers – Historically these alloys had part of the copper content of the traditional sterling silver composition replaced with cadmium (usually about 2%). This gave an alloy which was about 10-15HV lower in hardness than traditional sterling silver which had excellent deep drawing and stamping characteristics. Cadmium containing silvers are now prohibited by worldwide legislation and attempts to create similar alloys by simply replacing the cadmium with tin or zinc failed because the oxides of the tin and zinc, formed when torch annealing, were very hard to remove. Some manufacturers now use Britannia silver (95.8% silver, 4.2% copper) as a spinning silver because of its lower hardness.

Deox silver alloys – These are alloys developed primarily for casting applications and their properties were recently reviewed in an excellent paper presented at the 2010 Santa Fe Symposium by Joerg Fischer Buhner (click here to download pdf). Some of the copper content of these alloys is replaced with zinc and/or silicon with the aim of giving bright, firestain free castings. While the silicon and zinc additions do limit the formation of firestain it is not always a complete success. The higher silicon content alloys can be more difficult to cast consistently and cannot be fabricated easily limiting their use; whereas zinc is well documented to fume at typical investment casting temperatures. These alloys are an improvement on the traditional silver composition for investment casters but have no significant benefits for the practicing silversmith working with sheet and wire.

Platinum group metal additions – these are additions of either gold, palladium or platinum which replace some of the copper content of the traditional sterling silver composition. Aside from the considerable cost implication of replacing copper with a precious metal it has yet to be demonstrated that an alloy which contains an addition of one of these elements has a significantly improved tarnish resistance compared to the deox alloys detailed earlier. Gold additions make the alloy more yellow; platinum creates difficulties on melting and increases the potential for hard spots to form and silver alloys containing palladium have shown sensitivity to ultraviolet light when tested under ‘showroom’ conditions.

Alloys containing germanium - the mechanism by which the germanium content of Argentium silver alloys protects against tarnish and firestain by forming a transparent germanium oxide is something that I will discuss in another blog. Our work has shown that the composition of the Argentium silver alloys with about a 1% germanium addition optimises the mechanical working and casting characteristics of the Argentium silver alloys while giving exceptional tarnish resistance and firestain resistance. Other alloys may contain germanium, but these are limited to contents below 0.5% germanium because of our patent protection and they have to rely on supplemental additions of zinc and tin to try to match the performance of Argentium silver alloys.