Found this today, Someone tried Nik A Date that didn't work. I used my process and even the stain was removed. About a 2 hour process.
Sorry, I generally never try to clean my coins because I do know that in most cases, its best to leave as is unless you know what you are doing. Therefore, I have not looked into all the specifics of these substances reactions when coming in contact with coins. You still never answered my question!
I use Vinegar and 40 vol. Peroxide which is usually only available at beauty supply stores. If you have a coin with no date, do you really have something to be concerned about? This is, and always will be, a 1918 D Buffalo Nickel. You can't dispute that. It is beyond me why the coin collecting world treats them like a Redheaded Stepchild. Antique coins are identified using similar processes - almost to the point of tooling. My avatar is one of those (no tooling though). We don't seem to have a problem with them. I have dozens of restored Buffalo Nickels. I have one set that is almost all restored coins.