Group 11 element Parkes process. These metals, especially silver, have unusual properties that make them essential for industrial applications outside of their monetary or decorative value. They are all excellent conductors of electricity. The most conductive of all metals are silver, copper and gold in that order. Silver is also the most thermally conductive element, and the most light reflecting element. Silver also has the unusual property that the tarnish that forms on silver is still highly electrically conductive. Copper is used extensively in electrical wiring and circuitry. Gold contacts are sometimes found in precision equipment for their ability to remain corrosion-free. Silver
Coinage metals well known in the Persian and Sassanids era. Most notably, in Susa and in Ctesiphon. However, there are many more, even for coins made from intrinsically precious metals. Precious metals are always used in bullion coins and some collectable coins. Coins not intended for circulation or for intrinsic value have also been made experimentally using an even larger variety of metals, since they function as fiat money. In general coins intended for circulation must have metal values considerably less than their face values, for reasons discussed below. Coins that are intended for circulation have some special requirements based on the