@gman, recall that quarters are clad not plated. An easy way to determine if one is actually missing a clad layer is to get a weight. If it is within mint specs, then this would just be environmental toning.
"If you climb a good tree, you get a push." -----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed." -----King Adz