Looks like discoloration from some sort of environmental or chemical exposure. Possibly copper electroplated.
So, I guess I wasted my time posting to the duplicate thread to this one. Why did you post it twice? Chris
No offense is intended because we get this type of comment a lot, but when someone says it seems, thinner, thicker, heavier, lighter, bigger, smaller, etc it all translates to "I haven't got a clue." Any type of subjective comparison is suspect. Many times we get people giving us a subjective comparison when a simple objective test such as weighing or measuring a diameter would put the matter to rest, and we waste six pages or more trying to get the answer to a simple objective test, and then when they finally give it it proves conclusively that their subjective opinion was completely wrong. (Someone insisting that their 1974 cent is made of aluminum because it is so much lighter than a regular cent, and when they finally do weigh it it turns out to be HEAVIER than an average copper cent. 3.2 grams instead of the .9 grams an aluminum cent would weigh.)