I read somewhere that pure iron does the same thing.
The reason it rusts is the impurities which are almost always in it.
Some of those impurities are the reason “Damascus Steel” was so highly prized in times gone by. So a good look at this process is most informative, as it might conceivably be transferred to other areas.
Well, and besides the fact that I look forward to using this quite soon to certain projects I have in mind as I develop more constructs...
Certainly better-looking ones, at the very least. :)