I\'d say it needs a good bit more contrast right off the bat. Darken up the shadows with glazes of blacks, blues, and browns or by using inks, and then glaze in some brighter metallics on the parts that would be hit by your light source. If you use paint to glaze rather than inks, you can concentrate some browns like dark flesh around the rivets and such and it\'ll give you a nice, worn, rusty look.
