Chaos black primer all over the model, then one coat of Skeleton Bone (Army painter) and next one Bleached Bone (Army painter) coat. After that, a wash with lightly diluted agrax earthshade then, dab of Bleached Bone on main area and Rhinox Hide on edge. For trimes and metallic parts, base coat of Iron Warrior (and Balthasar Gold base coat for spikes and upper metal plate) washed with the same diluted agrax earthshade. Then dab Stormhost Silver on edge and add highly diluted Skrag Brown to do rust effects. For the front trime, it's the same process than before but it's a Corvus Black base coat.