Oxalic acid also works. It's found in wood "bleaching" and "brightening" products typically used on exterior decking.

As Mark stated, Naval Jelly can create a mild etch, which is removed as part of the polishing process. When applied to pattern-welded barrels after polishing, it can serve as the initial etch, right before the rusting process begins.

Here's what that look's like, right before rusting:



After:



Ken

Last edited by Ken61; 04/15/15 08:50 AM.
I prefer wood to plastic, leather to nylon, waxed cotton to Gore-Tex, and split bamboo to graphite.