I have a 1979 Proof Set which has a spot on the reverse of the penny. Almost looks like a burn spot. I can't send a scan of it... my scanner bit the dust recently. So I guess my question is what could cause this spot ? My coins almost never see daylight and are stored at very low humidity. Plastic caseing it came in never has been openned or cracked. Can this happen to my other sets? All replies welcomed. Thank you The spot is about an eight of an inch in diameter.... not perfectly round either.
I suppose it could be the result of some impurities, left on the coin, when it was issued from the Mint. Copper is very reactive, and coins can become spotted even if kept in semi-airtight holders at controlled temperatures. (just a guess)
I have seen a number of proof sets that have had different types of toning, carbon spots, or other differences. I agree with Jody. I think it is the metal reacting with something that was on the coin when it went into the slab.
The cent in my 1999 proof set has a very similar sounding spot on it. I check on it from time to time and it hasn't gotten any bigger or anything so I'm not too worried about it. Looks kinda neat, actually... Rachel
