Seated Lib 10c with some kind of stamped design on the back

Thanks! That's quite brilliant. I will try and post the results here

 

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I would try acetone first? It does no hard to the coin and might take a lot off.

 

Vaseline is a much gentler solvent than acetone, although on silver coins, I tend to use acetone first. Often, when you wipe a copper coin clean from its vaseline, the rag comes out somewhat green, it has removed very light (overall) corrosion you didn't even see when you started.

 

Not stamped, engraved reverse