It's called toning. Coins turn a blackish color when they've been in the ground or some equally dank, dark place. Natural toning comes in different colors, patterns, etc., depending on the environment and storage of the coin. AT (Artificial Toning) is done by unscrupulous people looking to make a quick buck. How they do it I don't know, nor do I wish to. You have been a member on Coin Talk only for a short time. If you're interested, we have had threads on toning quite a few times. Do a search on this site and you'll find interesting and educational threads on this topic. https://www.cointalk.com/threads/th...artificial-questionable-toning-thread.326881/ This thread is interesting. Here's one that's current. It's open now. https://www.cointalk.com/threads/the-toning-premium-thread-part-2.299570/page-324#post-3736317
