Birchwood/Casey Prema Blue Pen
I have used one of these for many years. It is KISS simple and works like a charm. Key point is to decrease the area first. I highlyt recommend this item.
Birchwood Casey offers you the best ways to
touch up scratches and worn spots or even completely reblue most guns. It will
give a non-streaky, even blue-black finish to steel (except stainless). Both
Perma Blue Liquid Gun Blue and Paste Gun Blue provide great blueing to metal
that has already been thoroughly cleaned and is free of rust. Perma Blue Paste
Gun Blue is slower to darken than Liquid Gun Blue, but will build up a denser
finish. NOTE: PERMA BLUE Liquid Gun Blue will not blue
stainless steel, aluminum or non-ferrous metals.
- See more at: https://www.birchwoodcasey.com/Refinishing/Metal-Finishing/Perma-Blue®-Liquid-Paste-Gun-Blue.aspx#sthash.V9hY7Yal.dpuf