Does anyone know a product that I can use to darken the bottom of a stainless steel (I think) mag baseplate? It's for a Sig p238 mag like the one pictured below:

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The pistol itself has a dark finish (not blued, sort of a dark gray parkerized) but the baseplate is shiny as hell. When I pocket carry the Sig in my hospital scrubs (!!) the butt is very near the pocket opening and shines out like a beacon. I don't need to do the whole thing, just the bottom outside of the baseplate is all I need to darken. Any ideas? Don't want to simply use paint or anything else that will gum up the works.

Thanks in advance!