Well, I picked up a bottle of Testor's gloss black and flat black enamel and "inked" the heavily engraved receiver of my o/u. The effect with either was very pleasing--while it lasted. The enamel washes right off--as you might expect--at the first touch of CLP or RemActionCleaner or other solvents commonly foound around your guns. What might be a more persistent paint to use?