To that end I tested and found several products helpful:
Army Painter colored primers. One coat of blue, one wash of black paint and I was well on my way to being done. Thank you Army Painter, thank you.
Vallejo Verdigris Glaze, a super concentrated paint that simulates patina easily. (tutorial behind that link) Just remember a little goes a long way. I was using about as much paint as would fit on the point of a pin, and then watering it down. Try it out before using it too much, it works but it has a different consistency from most acrylic paints.
Rusted, patina-ed and bloody, here he is. Be warned, the full size view looks poor due to the massive amounts of washes and competing colors that blend at more than microscope distance away.
Awaiting a legion symbol on the shoulder. Fresh rust on the paint chips near the ankle.
Requisite lightning bolt, massive patina on the chaos star, paint chipping on leg and toe of the boot.
Slightly blurry pic showing the fresh rust on the backpack spikes, old rust on the wings, as well as the patina in the piping on the greaves. Note the blood effect from the bayonet is used on the pouch and flensing knife at his hip.
