Rapid Toning Of Lincoln Memorials

I had something similar happen to me recently. I opened a 1968-S roll and they were all MS-64 to MS-66 and bright, bright yellow -- almost like gold coins -- and had full mint luster. They were beautiful.

I laid them out face up and got back to them the following week: They had all lost the bright gold tone and were turning more of a copper tone. Not a lot but definitely a change. They were not exposed to direct sunlight and I don't live in a high-humidity area. It's actually very dry here.

I wish I had taken before and after pics. I was surprised at the change because, as BadThat posted, copper takes time to change state and oxidize.