Could this possibly be a partial missing clad layer?? For you wise guys, I already know it's really dirty!!!
Nope, staining/corrosion. Remember, missing clad is rare, missing clad on both faces is much, much rarer.
This reminds me of a coin I had that I thought was missing the clad layer, but the weight was the same. I wonder how coins get that copper-colored dirt all over them.
Well, not rust as such (there's no iron in the coin), but a metal oxide like rust. Same idea, and sometimes similar appearance.
Long term environmental exposure to the Clad coins and Nickels to the elements. Both are composed of Cupro-Nickel. The Copper tones over time. I've been metal detecting thousands of them for over a decade. Here are some examples.
Our fellow enthusiasts have offered good suggestions. It's also possible to create conditions to cause copper from one coin to transfer to another, like building a battery in science class.
