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). Perma Blue® Paste Gun Blue provides great blueing to metal that has already been thoroughly cleaned and is free of rust. Perma Blue Paste is slower to darken than Liquid Gun Blue, but will build up a denser finish.