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.