The
Foul Out's patent has expired, but reading it is a valuable learning tool.
First, it is perfectly possible to etch a plain steel bore with these homemade systems. The Foul Out patent explains that only limiting voltage to 0.3 volts will prevent this and that is what theirs does. To work at that low voltage you need to use something better than just ammonia and vinegar. The patent gives the original formula that provides both ammonium acetate and the acetate salt of the metal to be etched so as to get those correct ions in place in the conduction path. Outers later revised it with surfactants to better remove the powder fouling that is between layers of copper.
I designed a proper 0.3V regulated device for Father Frog awhile back. You can download my design,
here. The electrolyte will not boil. It will not remove steel unless there is rust in the bore when you start. If the solution turns brown,
STOP because there was rust in the bore and the presence of those iron ions is now carrying iron to the center electrode. Stainless is probably immune to the etching problem because of the same chromium oxide surface layer it has that prevents rust.
The original solutions from the patent below. I like to add a drop of Kodak Photo-Flo to them for better wetting. Dawn dishwashing liquid would probably work, too.
Copper Solution
562.3 grains Ammonium Acetate
51.3 grains Copper Acetate or 58.3 grains Cupric Acetate Monohydrate
Add distilled (or high megohm deionized) water to make 1 Qt.
Lead Solution
562.3 grains Ammonium Acetate
95.0 grains Lead Acetate or 110.8 grains of Lead Acetate Trihydrate
Add distilled (or high megohm deionized) water to make 1 Qt.
Back about 1989 the Cast Bullet Associations publication, The Fouling Shot ran an article on a flashlight voltage cleaner and the author cleaned a chrome moly steel bore with it. A few days later it was coated in rust because the surface etching had activated the steel. I can't recall his particular solution, but by then Outers had warned them off by virtue of their patent still not being expired at the time, so the recommended against the thing on both scores.
Hope this helps.