All of this talk of Lincoln being baked....is he staring in a Cheech and Chong movie I am not aware of?
Actually I have tried to clean ancient coins by putting one (only one) in a glass of water and microwaving it...the water just boils. If there are two or more, they want to spark!
Two or more make an antenna with a spark gap, and there's a LOT of power available to feed the arc that results. Still not as much fun as the time somebody in the family put something in a plastic bag into the microwave -- without first removing the wire twisty-tie. Now, THAT was an antenna, and an arc!
And let that serve as a warning to all you aspiring coin doctors out there, you want to practice safe artificial toning!
Might as well, it'll be a million years before these are scarce. We'll be the Caveman cavemen by then