Anything with soot should work, acetylene just gives off alot. One old article mentioned using an old wine cork, not sure why... Red wine makes it burn red soot maybe? Lol! Or just alot of soot from the cork.
I'm thinking the epoxy of the clear permeates(soaks) right through the soot for adhesion. It is only lightly misted charcoal after all
Surely if you raided your fire-pit and put on chunky hand prints, it might not hold.