mike wrote in
:

I STR reading somewhere that the red oxides get converted to black
oxides - my experience has been
that most of the black stuff just rinses off and a couple swipes with
a wire brush takes the rest of it off.

The old fashioned way of producing black iron oxide finishes on firearms
was "rust" bluing. You chemically rust the surface, which gets you Fe2O3
(the red stuff). You then boil the part, which converts it to black iron
oxide (Fe3O4). Rinse & repeat. Black iron oxide is like anodizing, in
that it seals the surface & is non-porous. It also doesn't flake off the
way the red stuff does, so once you've got a good coating of the black
stuff, it won't rust anymore.

You can get rust blue chemicals from gunsmithing suppliers like
Brownells. I did a piece on my Clausing mill with some, and although it
took a while to process, it looks great and hasn't rusted a bit.

Doug White