"Phil Hansen" wrote in message
...
What is the process called that gives that blue color to steel. Looked
at parkerizing but it does not seem to be the thing. I remember
something about heating up a part and quenching in some sort of oil.
Want to take old bolts etc, clean off the rust and then coat them with
this black coating/covering/protection.
Any help appreciated

Several ways to get the blue color.

Cold Bluing. CLEAN metal, apply. Generally has copper somewhere in the
formula.

Hot Salts Bluing. Several formulas, ranging from simple nitrates to
cyanide. CLEAN
metal and cycle through several heated tanks.

Heat bluing. CLEAN metal. Heat to desired color. Quench. Works best on
small
parts---screws, pins etc.

All of the above require CLEAN metal. Really clean---see yourself in the
shine. NO
grease, fingerprints, etc.

For your rusty bolts the blacksmithing practice of swabbing on a coat of
some mixture
of beeswax/linseed oil/other oils/"secret ingredients" might do the trick.
Done to hot
metal, it leaves a smooth black surface.