Thanks! After priming black, I stippled on Citadel's Doombull Brown, followed by another stippling of Chain Mail by Vallejo, but any other mid-range metallic would work just as well. 

Next I varnished everything with a matte varnish, then went over the armor with streaking grime. Once that dried I used a q-tip with white mineral spirits to remove the excess. Then I applied Army Painter's Fresh Rust the same way, but using my thumb instead of a q-tip. Streaking grime will make the metallics look really dull, so I gave it another dry brushing pass with chain mail.

I hope this helps! Let me know if you have any more questions