Citric acid 910%) works as well as nitric and is much safer - see -
http://www.finishing.com/0800-0999/909.html


On Thu, 25 Sep 2003 09:53:52 -0700, "Steve" wrote:

I use a weak solution of nitric acid to passivate stainless. (I don't
remember, off hand what the mix is. I just keep about 5 gals mixed in a
plastic drum and hang the part in it for a few hours.)

A welder friend has a jelly solution that has nitric acid in it. He brushes
it on a finished stainless weld and lets it set for a couple hours then
rinse it off. Really cleans the weld effected area and never seems to rust
afterwards. Very expensive (about 15 bucks for a half pint jar.)