WHY DOES SILVER TARNISH?
Tarnishing is a natural process which is caused by oxygen, moisture, sulphur and other particles in air coming into contact with various types of metals. Tarnish is a thin layer of corrosion that quickly forms over your silver jewelry, resulting in the formation of a dark coating that is undesirable to look at. Tarnish is basically the dulling of silver that typically occurs as a chemical reaction with oxygen, hydrogen sulphide or sulphur present in the atmosphere. Sterling Silver is an alloyed metal, normally made of 92.5% pure silver and other metals; but it also tarnishes quickly because of its composition. Tarnishing happens as a natural consequence of the molecules in silver interacting with the molecules in sulphur.
The reason Sterling Silver tarnishes more easily is because pure silver has been alloyed with copper. Chemically, pure silver is not very reactive. When Sterling Silver is exposed to airborne compounds of sulphur, black tarnish will slowly start to appear. When exposed to low level ozone, silver oxide forms. Tarnishing can also occur due to silver being exposed to salt, direct sunlight and chlorinated water. Silver chains, necklaces, rings and bracelets can tarnish easily from contact with lotions, perfumes and perspiration. The presence of sulphur and amino acids that can be found in perspiration can cause discoloration of Sterling Silver jewelry.
Note: All precious metals can tarnish to some degree. Platinum and pure gold are the most tarnish resistant metals and will show very minimal (if any) tarnish over many years.