What causes the "Rainbow" toning on pennies?

magazineman

In a collection I just purchased there were several rolls of 1964-1966 uncirculated pennies. They were still in the original paper rolls. (Neat old papers) I opened a few for fun and they had somewhat of a "dusty" feeling to them and had darkened. I assume that was from the old paper? There were also several that had beautiful rainbow toning to them. Is this caused by the old paper rolls? Thanks

7Jaguars

This is generally thought to be sulfa/sulfide compound oxidation on the surfaces of coins. In your case that would be NT, but the coin doctors sometimes "cook" coins literally in the oven or window sill with paper to give coins that look as well. There have been many posts on the famous Taco Bell napkins....

ThePennyLady

Coin roll wrappers often contained sulfur which can cause the coins to tone, especially copper, and some end up with very pretty colors.

OneCent

Sulper, Time and a lot of luck!