With my last WIP of my Knight, a couple of you were interested in how I'd done the brassy bronzey armor plates. Well, here's a quick recipe to get you started on your own tarnished/burnished combo.
Step 1: I used Vallejo's Tinny Tin as the base coat.
Step 2: Highlight with a mix of Tinny Tin and Vallejo Brassy Brass.
Step 3: Highlight with Brassy Brass.
Step 4: Begin shading with thinned wash of Vallejo Charred Brown mixed with a little Black.
Step 5: Continue shading by adding more Black.
Step 6: Once you are satisfied with the depth of your shading, take it one step further with a thin glaze mixed from two Secret Weapon washes - Storm Cloud and Algae.
Some of this may be a little tough to see in the color swatches above, but it works pretty much in that progression. Of course, feel free to add a few more "in between" steps if you feel the need.
I hope you have fun with it!
And I wasn't sure if I'd shown you the updated insectoid-walker for my army. It has previously sported green armor plates and has been used as a Defiler : )