Brownells Oxpho-Blue Liquid Gun Blue, Cold Bluing Solution, Gunsmithing Tools Maintenance Cleaning Supplies, Professional Grade, 4 Fl oz. (118.2 mL)

Absolutely no after-rust, Ease of application and remarkably superior results, With Oxpho-Blue, all you need do in most cases, is dampen a piece of cotton flannel and give the area a good rubbing