More importantly, is it the heat thats important, or is it what the coal shovel was made of, or exposed to during its lifetime that made this work

Otherwise just slam the penny on a red hot electric stove burner..
I think it's the Extreme uniform heat.
It reads like the coin must get Red hot.
and of course once it cools down, it most likely is a slug again.
and it will take away the nice green toning.
but as I say......
What's the difference between the value of a Slug ?
and a Slug you know for a fact is a Chain Cent ?
Definitely a few bucks & the high of knowing
I do wonder if it only works on Non Dug Coins though.
like Nic-a-date doesn't work so well on Dug Buffalos
because the ground seems to change the molecules after awhile
(molecules ? Is that the Right Word ? )
besides coins, I have heard of people Cleaning Rust with fire.
I've actually tried using heat in the past to clean relics, by placing them in the coal stove.
But other then turn them Black,
I don't remember much Progress there.