Birchwood Perma Blue Liquid Gun Blue is the best way 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 will not blue stainless steel, aluminum or non-ferrous metals.
This product contains chemicals known to the State of California to cause cancer and birth defects or other reproductive harm. www.P65Warnings.ca.gov