Flitz, toothpaste, Blitz, jewelers' rouge, 40 grit sandpaper, 0000 steel wool, grinding wheels, and steel wire brushes are all abrasives, it is just a matter of degree and how well you look for scratches. People will swear that 0000 steel wool will not scratch; I say use 100 power magnification and you will see all the scratches. I recommend copper or brass wool; they won't scratch steel, but will remove bluing if used enough.
Yes, OCD1, your blued guns are still blue, but they have less blue than they did before you used Flitz on them.
Contrary to what one poster said on that old thread, cold blue is not paint. Caustic blue, rust blue and cold blue all do the same thing, oxidize the surface layer of the base metal. The difference is in the strength of the oxidizer used which determines how deep the oxidization goes and how permanent the blue color is. The actual color depends on a lot of things, including light refraction which in turn is dependent on the degree of polish before bluing.
Jim
