Bob, here's the blackening solution info I promised earlier:

Ultra-Blak 420 (for copper/brass), from Electrochemical Products, Inc.

http://www.epi.com/black-oxide/hot-o...ening.html#420

Edit: Just tried it out on a test piece. Made a uniform, black coating in about 30 seconds (maybe less) over a 2 inch square plate. Feels pretty stable (does not flake or chip off easily; doesn't scratch with a fingernail), but I have no idea if it's any good for corrosion resistance.