That's what I was going to suggest.
Been a while since I've looked but I worry that the saltpeter might be a little hard to find in the modern paranoid era. Used to be at any drugstore. There are alternatives.
you can dissolve black powder in water and get a nitrate solution for treating paper. The part that remains on the bottom of the bottle is powder charcoal. Remember black powder is 75% saltpeter
cheers mooncoon



























