Earlier form of blueing. Look at black powder firearms and you'll see some. Birchwood Casey makes a "Plum Brown" solution. When you hear of a weapon having a "patina" it refers to metal that has rusted slightly, been wiped down with oil, rusted again, so on til the whole thing, or much of it, has a thin coat of rust carded ( carding refers to knocking most of the rust off - by steel wool, sandpaper, hand rubbing etc. ) off and oiled til the thickness of the rust is sufficient to soak up enough oil to prevent further rusting. The difference between patina and browning is that patina just happened in the course of using the thing. Browning was done evenly and on purpose. It's kind of funny that just the right amount of rust holds enough oil to prevent further rust given reasonably regular maintenance, like parkerizing.
Hey, who do you think knows more about the oxidation process than a guy named Rusty?
[This message has been edited by Rusty (edited 09 November 1999).]