I found this 1968 Lincoln Penny, sorry for the blurry pictures, and the obverse of my penny is very shiny, almost mirror like I think it's safe to say, and the reverse is the complete opposite, it's more dull brown. Why is it like this???
Could be a few reasons. One I could think of is that someone buffed the Obverse and not the Reverse. I can truly tell you that it is not a Mint Error of any kind.
I find that coins kept for long periods of time in rolls, the end coins tend to age differently than the inside coins. That would effect one side of two coins at each end of the roll. Just my 2 cents! Haha...
Maybe it was laying down on its obverse for a long time, keeping the shine while the reverse was environmentally toned.
It's man made do not a mint error. There are several reasons as to why but to me it doesn't matter as it's only worth face value.