Coins, stamps and antique weapons are certainly not the same thing.
I would not know a stamp can be restored; it surely demands high expertise.
But i have gathered coins for a couple years (before i sold them to afford gathering antique weapons). While restoring coins, for what the strict term means, is new for me, the act of cleaning them, as presently said not to adviced, is unclear for me. I took it that coins are classified by the integrity of their graphic or pictorial contents, as well as their metal structure. The various catalogues i knew available defined their such condition in (at least) four different grades, from scrap to pristine, and respective collecting & market value. But i have never heard that cleaning (read washing) the dirt of a coin would 'damage' its value. But then, i have never nagivated in a high end collecting universe, and therefore i ever ignored what was prohibited
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