Some consider toning damage. It can be cause by heat like mentioned above or it can get like this from sitting an an older style album for years. Looks rather nice to me and I would keep it
The toning does not appear to be man made. I agree with @SlipperySocks in that this nickel was probably in a older album and toned this way due to the chemicals in the paper/cardboard. I think the toning is great, if you are a collector of toned coins. I'd say that is a keeper for sure.
@Fred Weinberg I would love to learn more on how to tell the difference between artificial and natural toning. Will you share what the cues are that you see to determine AT on this Nickel?
I would never think to speak for Fred, but AT is really almost impossible to prove and we are left with opinions and I trust his. Generally if it looks too good to be real, it is.
Hard to verbalize, but it's not natural. I guess viewing natural toned coins, of any metal, would be helpful to then be able to determine what isn't natural. I'm closing my office in two minutes, so I won't be able to add to this, or reply, till tomorrow morning. (quickly - natural toning has 'cartwheel luster' usually - a term used mostly for silver dollars, but applies to other denominations also) I'm sure others here can also contribute their thoughts.
