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Message:: [QUOTE="Insider, post: 2624647, member: 24314"][USER=12789] Doug is correct.  In fact, @SuperDave has posted a great definition of "Patina" illustrating an understanding of the subject: "I have the impression of "patina" as some natural chemical aging process related to interaction of atmospheric chemicals with the metal of the coin."   He has just described toning (a type of patina) and that's what the gray colored "patina" is on the dollar. I was taught that ANY oxidation, including corrosion such as RUST, can be considered to be a coin's "patina."  However, we don't associate/use such an "artful" word in cases of terminal corrosion. :D As Doug wrote, the word is mostly used to describe the greenish surface found on ancients.  Collectors even describe the color of the finish on old wood using the word "patina."  For that reason, members may wish to expand their thinking about the term. Finally, the green on the dollar is not patina.  It is a spot where surface corrosion is beginning.  It should be removed before it eats into the surface.  The coin needs conservation.  I know that at least one of the secondary TPGS (ICG) would have contacted the customer for permission to remove the contamination (for free) before slabbing the coin.[/user][/QUOTE]