I would say that plating another metal , as an outer layer , onto an object made of metal , is another subject ( copper , nickel , chromium , cadmium , zinc , whatever ) .
In terms of "controlled oxidizing of steel" , I would submit both bluing ( especially the old-old way of doing it ) , and parkerizing ( should Parkerizing be capitalized ? ) .
If you want to know about bluing ( fast , slow , hot , cold , traditional , modern ) you should check with both the restorers of top-quality antique firearms , and / or , the top-quality makers of modern custom firearms .
If you want to know about parkerizing , you should check with the folks who do award-winning restorations of fairly older Harley-Davidson motorbikes .
Both bluing , and parkerizing , can easily be done at home , if you have some space , plenty of time , some money for supplies , and excellent laboratory technique .
What ever you do at home , even if it's just cleaning your chain , please think about fumes , toxic residues , toxic waste disposal , etc .
I've read more than once , that bluing done with the one of the old original processes , and done by an expert , and done to perfection , takes about 50 years to stabilize . Up until about that time , the older it gets , the stronger , and the more beautiful , that bluing becomes !!
Parkerizing is seen mostly on old nuts , bolts , and tools . It is a very dark brown finish . It is permanent , and does it's job of preventing rust , as long as you keep it out of the direct weather . If you leave your 1947 Harley-Davidson sitting out in the sun and rain and snow , and you don't wipe the nuts and bolts with an old oily rag once in while , eventually the parkerizing will give up , and those nuts and bolts will start to rust badly .
Cheers ,
Raoul Delmare
Marysville Kansas