When cheap German SA 22s came out in the 50s, my dad would get one and strip it and dip it it wax. Then he had little tool he made to “engrave” his art through wax. He dipped the parts in acid.
Don’t know what it was but I think some type for batteries. Flushed with distilled water, also free in battery room at work. He then heated up guns to remove wax. He had a little jig to hold cylinders while he worked on them. He did quite a few and run them on tip boards at work. I tried it once on a beat up Buffalo Scout 22. My squirrel on branch looked like a rat on a outhouse plank.