Sterling Silver Jewellery
I’ve been using the expression ‘sterling silver’ all my life without really understanding what it means. Finally, I looked it up. Sterling silver is an alloy of silver containing 92.5% pure silver and 7.5% other metals, usually copper. The minimum millesimal fineness is 925. Stuck again, I had to look up the word ‘millesimal’ and I found that ‘millesimal fineness’ is a system of denoting the purity of platinum, gold and silver alloys by parts per thousand of pure metal in the alloy.
Fine silver is 99.9% pure and is generally too soft for producing functional objects or jewelry, whereas in sterling silver the silver is usually alloyed with copper to give strength whilst preserving the ductibility of the silver and a high precious metal content. Other metals can replace the copper, usually with the intent of improving various properties of the basic sterling alloy such as reducing porosity caused by casting, eliminating firescale, and increasing resistance to tarnish. Firescale is a reddish purple stain that appears on silver and copper alloys such as sterling silver when they are heated in the presence of oxygen.
Other replacement metals used to produce sterling silver include germanium, zinc, platinum and a variety of other additives including silicon and boron. A number of alloys claiming firescale and/or tarnish resistance have appeared in recent years sparking heavy competition between the various manufacturers and their different formulations.