Regarding chemical reactivity, many populr brands are actually paint. That's why they wear off and always presents a seam where it meets the original. Plus, they stink. Van's will go anywhere where bare ferrous metal is present and not cut in over previous oxidation. The surface must be completely free of any oils...completely free...and use a toothbrush, over and over until you get the color you want. Do not use a Q-tip, as there is lanolin sometimes in there. No finger oils on the surface, either, or you'll get a nice print suitable for an FBI file.
One of the things we do for food is buy decent pistols lacking finish but with no pitting. Then we spend an afternoon doing a few and off to the show. Never a complaint. Never a question. Can simulate parkerizing too with a coarser blasting medium.