Just scored this amazing JFK half dollar. It was left in the annealing ovens far too long. This causes metallic atoms to migrate within the coin, and copper is drawn to the surfaces. The copper you do see is blazing, screaming red with a blinding shine. Also has dull grey spots as well. Very rare on clad half dollars, and I have never seen one quite like this. Surely there have to be more as they don't heat these one at a time. Anyone ever seen one like this? (Please only post half dollars).
Wow, that looks severely corroded on the cupronickel portions, and mechanically disturbed at the borders between the copper and cupronickel areas. I can't imagine how metal migration could've led to that appearance -- but, as I said in another thread, I'm not a metallurgist, so that's not at all surprising. Very cool example! I like coins that make me wonder... Edit: I wondered if the "corrosion" could be from galvanic attack on the nickel in contact with the exposed copper. But if that happened, it would happen all the time on clad coins, which all have copper exposed around their edge. Edit 2: To clarify, I don't know how metal migration would produce this result, but I have no alternative explanation, so, "sounds good to me"...
1. Atoms of different elements react differently under heat. 2. Not every mixture of a clad layer is precisely the same, including the exact percentages of the metal it contains, level of impurities that were mixed in, etc. 3. Not all improperly annealed coins were over-cooked the same length of time. 4. Improperly Annealed coins all vary from one to the next. Some are uniform, some only one side, some in spots, some in swirls, amd vastly different colors. Hope this helps
No. I am not going to send it in. If i am 100% sure it is a real error, I don't spend $60-$80 to have a TPG tell me something I already know.
The coefficient of expansion is different for different materials and that could cause some of what you see.
