I know it evaporates steve199 but it's still an additive on the coin. Maybe it doesn't do any damage to the coin at all. I might be very wrong but I just don't thing it's right and still consider it altering. When I buy a coin the first thing I do is " NOT " buy it if it has a chunk of something stuck on it. Second, unless I found the coin and it has something stuck on it but I like the coin then I simply put it in my (not the best quality coin) section.
Everyone does what they want to their coins and everyone has their own opinions. I've only collected for 11 or so years. I wish I knew all the answers to everything but all I can do is speak/write my mind out.