This is the first post in a series of to educate you about silver tarnish, what it is, how it happens, how to prevent it, and how to clean it. There is a lot to cover, so we will break it up into multiple posts.
The simplest description of silver tarnish is the darkened appearance of the metal that happens over time. In the picture, the charm on the left has some severe tarnish.
There are lots of factors that we will discuss later that cause silver to tarnish. New clean silver has a bright white appearance. As it is exposed to the environment it starts to darken to a greyish or brownish color and can eventually turn almost pitch black.
What is that black substance we call tarnish? Tarnish is just a descriptive term that means the lack or loss of luster. If we want to clean and ultimately find ways to prevent silver tarnish, we need to understand what it is and how it is caused.
Silver tarnish is a type of chemical reaction, often incorrectly described as oxidation of the silver or called silver oxide, it is silver sulfide. But that's not a complete description of what silver tarnish is. Another part of silver tarnish that seems to be missed in other online descriptions is the reaction of other materials in sterling silver, the most common silver alloy. Sterling silver is 92.5% silver. The remaining 7.5% is primarily made up of copper, a material that tarnishes very easily. By itself copper seems to tarnish very easily, more so than pure silver. I will have to do some more research, but I believe that the copper is creating some copper oxide and other sulfide compounds that contribute to the tarnish.
If you put a piece of fine silver and a sterling silver side by side, the sterling silver tarnishes mush faster. Based on this empirical observation, that small amount of copper is playing a larger role in the tarnishing reactions. While many discussions online solely talk about silver sulfide as the main culprit, there are at least two metals that comprise sterling silver and can react and contribute to the tarnish you observe over time.
To be continued...