You will need:
Finished Painted Model
Devlan Mud GW Wash
Gryphonne Sepia GW Wash
Oxide White Pigment Powder Secret Weapon Weathering Pigment
Tamiya Weathering Master Snow, Soot Rust
Tamiya Weathering Stick Snow
First take your model and lightly add Gryphonne Sepia to the model in various places. Make it only just enough to notice do not go overboard on the wash.
Next take Devlan Mud and do the same but even less than the Gryphonne.
Now finally add the weathering stick to the model mostly on the top of the medal and on the backpack.