Why does Silver tarnish?

Silver naturally reacts with hydrogen sulfide in the air to creat a very thin layer of tarnish. Hydrogen sulfide can be found in items such as wool, fossil fuels, foods such as onions and eggs, and materials such as rubber, paint and latex and some small amount are naturally present in the air. High humidity climates, such as in Singapore, will accelerate the tarnishing process. Depending on the finishing of the coins or bars, this process might occur faster or slower. American silver eagle coins tend to tarnish more slowly due to their finishing.