Thank you, Kutter. Guess I assumed NaCl or read it by someone else. The issue would be a fluid that was stable at the right temperature and with the right heat transfer rate in which to immerse the part (with a bit of oxygen present), would it not? The nitrates are powerful oxidizers, so they would have plenty of oxygen available. Come to think of it, maybe that is necessary to get the oxide film?

How do you do carbona blue?