Charcoal ash... dust to dust. On a different but similar level of insight is that the sky’s color is dust tintable and understanding radio or radar allows one to off color frequently. One day uniform Camo with color end as does the Bluejays feather.
He told me zinc had a lot to do with it.
My dad is the guy who developed the inkless check copy for Standard Register. He was a carbon research engineer who got his start in that department as a janitor. Inks and waxes for paper, autos, etc. was his life.