Here is directions on how to put a patina on knives.
A patina is forced oxidation that protects the knife form rust and the elements. I do this to all my carbon knives once the coating starts to wear. The process is simple fast and work awesome.
Plus you can add some unique charicter to the knife with a creative patina.
http://tbwpodcast.com/knife-patina-how-to-do/
Cool idea, I've used gun blue in the past with very good results.