How Does Silver Become Tarnished?
Tarnish is a form of oxidization. Other common forms of oxidation are rust and copper patina. Silver reacts with its surroundings to form a chemical compound called silver sulfide, better known as tarnish. Unlike iron and copper, silver requires more than just the air around it to tarnish. It requires sulfur. Sulfur is an element commonly found around us. It is in eggs and onions, wood, rubber, paint, and fossil fuels. Even should none of these things ever come into contact with silver jewelry, it will still tarnish over time. This is because, over the last hundred years, all the internal combustion engines in the world have thrown enough atomized sulfur into the air to instigate the oxidization of silver wherever it may be. A little known fact is that, prior to the heavy industrialization of the world, silver didn't tarnish unless it came into contact with sulfur some other way.
Silver jewelry which is only just begun to tarnish is easier to clean that silver which has become almost black with tarnish. Sometimes a simple rub with a clean rag is all it takes. However once the silver has begun to yellow, a chemical silver polish will be required. These liquid polishes are rubbed on with a rag and then wiped off. There is no real chemical reaction which takes place. Silver sulfide is less sturdy than plain silver. When silver has tarnished to the point of being brown or black, a chemical dip is needed. The exact chemical makeup of this type of dip varies, but it is always very caustic and extremely dangerous, both to people and to silver. Typically it is so strong that if you leave your silver jewelry in the dip for more than a few seconds it will eat through the tarnish, as well as the silver beneath, causing unsightly pits and pock marks. Nevertheless, a quick rinse in a chemical dip is sometimes necessary to break up the absolute worst of the tarnish, the rest of which can be removed with a lot polishing.
Silver is a very soft metal, as anyone who has owned a silver ring for a long time will know. It deforms very easily, and it is also easily removed. When you use a chemical dip, or silver polish, or even polish your silver by hand, you are rubbing away the silver itself. This is occurring at a near microscopic level, so it is highly doubtful that it would be noticed, except over more than a century of constant use. Even so, it is still happening and the level of detail on your silver jewelry would be slowly eroded as a result. One should be particularly careful when dealing with jewelry that is only silver plated. Such plates are only a few molecules thin, and will erode if polished too aggressively or too often.