Having finished the base coat on my Ork Fighter Bommer I gave the plane a wash consisting of Chestnut Ink, Scorched Brown paint (which helps remove the gloss of the ink) and some water to thin the wash down.
I am quite pleased with the end result. I was trying to get a rusty looking battered plane and I think that this paint job does do just that.
See the full workbench feature on the Ork Bommer.