Air layer Rough Iron @ 1:2 medium
Air layer Warplock Bronze 1:1 medium. Use to give directional metalic light from one angle
Brush layer Ratling Grime liberally onto deeper panels
Use Grim Black marker on deeper or partially hidden parts
Lightly brush Broadsword Silver onto all welding points, rivets and support frames. Dab away excess if needed
Detail brush Oil Stains at moving parts and surrounding grease zones Aiming for a "broken rock earth" of war torn armageddon.
Use Green Stuff putty to blend together as needed to get desired look.
Brush on Martian Ironearth and then lightly apply Martian Ironcrust to smooth putty patches.