Blue Lincoln Cent

What is the most likely cause of a Lincoln Cent (1930) to turn blue?

I know that exposure to sulfate will cause the copper to react and make a blue tone, but I also have read that cleaning a copper coin with cyanide will cause the copper to turn blue.
The 1930 cent is a coin that would fit the profile of a cent that may have been dipped in cyanide, so I'm not certain if this coin has been cleaned or perhaps it is really a blue uncirculated coin.  Does anyone have any knowledge of the frequency or likelihood of finding genuine blue toned Lincoln cents?  

7 years ago

In theory, any coin can tone to any color, depending on what is exposed to. I have seen blue coins that were "cleaned" with gun bluing.  Handguns are treated with a chemical that restores the surfaces that are attacked by heating from firing and from carrying it around in your pocket. That being as it may, it is highly unlikely that the coin turned blue "naturally" i.e., from ordinary exposure to the common environment. 

I do not collect US coins, but the easy advice to ignore anything that is not in The Red Book; and there are no blue cents in the Red Book.

7 years ago
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