That's a really interesting paper. Thanks for the link. I honestly didn't follow all of the chemistry, but I understand your point. However, isn't it the environment in some form or another that brings out the discoloration, including the black spots? It seems like there would be degrees of variation in aspects of the minting process, e.g. amalgamation, that would lead coins to react differently under similar environmental situations. Clearly, I see you demonstrated that the coin was not improperly cleaned. Are you saying such an example shouldn't be considered environmentally damaged either?