Quote Originally Posted by Roger Payneicon View Post
I've in recent years experimented with concentrated HNO3 & it works well, so long as you do not expose the piece for too long, as the acid will soon etch into the surface & cause pitting. You definitely need your sensible head on, though, when using such unpleasant chemicals......good gloves, face mask, eye protection, good ventilation etc.
When you say concentrated Nitric acid is it fuming when exposed to air? That would be the most concentrated form at about 21M. We experimented with fuming Nitric acid in our chem labs in college and it is very nasty stuff, only used in fume hoods and kept well away from water as it would boil, splashing nitric acid everywhere if water is added to nitric acid instead of the other way around.