Unless otherwise noted, all silver used by ELM Designs is sterling silver.  This includes all silver chains, ear wires, and ear wire backs.  Sterling silver is an alloy of silver containing 92.5% by mass of silver and 7.5% by mass of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925.  Fine silver, by comparison, is 99.9% pure silver, and is generally too soft for producing lasting pieces; therefore, the silver is usually alloyed with copper to give it strength while preserving the ductility and beauty of the precious metal.   Chemically, silver is not very reactive - it does not react with oxygen or water at ordinary temperatures, so does not easily form a silver oxide. However, it is attacked by common components of atmospheric pollution: silver sulfide slowly appears as a black tarnish during exposure to airborne compounds of sulfur (byproducts of the burning of fossil fuels and some industrial processes), and low level ozone reacts to form silver oxide.