I sprayed a grey primer on to my armour and then used a gloss Aluminum spray paint to finish. I added the 'dirty' look to my armour using watered down black acrylic paint applied with a damp sponge (make sure the sponge is one with larger air holes in it or this method won't work). I then add a dark silver (black and metallic silver acrylic mix together) using the same method to blend the black it in to the base colour.
Black was also used anywhere that should be in shadow for example where armour pieces over lap each other. The dark silver was used to blend it out. This was the same for any battle damage that was on show.
Hope that helps
Double H