Presto Mag Gun Blue is a cold blue formulation that works on all steel (except stainless steel). Specifically formulated for when you want a deep blue luster on your firearm’s metal surfaces. For complete reblue applications. - See more at: https://www.birchwoodcasey.com/Refinishing/Metal-Finishing/Presto%C2%AE-Blue-Mag-Gun-Blue.aspx#sthash.3kPYqzQB.dpuf