that was my initial thought. if you look at the reverse the discolored area drops below the finished surface on the rest of the reverse giving monticello a 3d look. Also, upon weighing the coin along with 11 additional 86 d nickels as a baseline and came up with average weight of 5.04 to 5.06 grams. The coin in question weighs 5.02 grams. of the 11 other nickels 5.04 grams was lightest.