https://www.reddit.com/r/AskHistorians/ ... urs_chain/Siin mainitakse liiva, õli, uriini ja äädikat:
"Was the process of rolling the armour in a barrel full of sand really used?"
Yes, that tactic really was used. If there no barrel and sand happened to be handy at the moment, another common method was some sort of sack with
sand/vinegar (and I've heard SCA guys say urine, too. ick), and it'd be vigorously shaken and moved around, and then oil re-applied.
Really though, the key to keeping armor free (well, mostly free) of rust was preventative maintenance. Keeping maille oiled made it a fairly messy affair, but a hauberk or byrnie that was oiled and then worn against a gambeson (thick, padded jacket) would cause it to rub around on itself, which is a sort of continual light-duty scrubbing.
A lot of metal armor would also be blued, via either the hot or cold method. "Hot" bluing involves quenching heated metal in
oil, which sort of suspends a protective coating on the outer surface of the metal, so nothing underneath it can rust. Of course, the method isn't totally 100% rust-proof, it only slows rusting down. Periodic cleaning and re-oiling would be necessary. Medieval armor was made from high-carbon steel, so frequent care and cleaning were pretty important.
"Cold" bluing involves flash-rusting the metal with something like
urine, making sure there's a nice, even coverage. Then, everything's coated with oil, which impregnates all of the little surface imperfections. Then they'd let it sit for a while, lather, rinse, repeat. The finish from cold-bluing isn't blue. Dark, black/brownish hues are more common.