The Brass Scorpion looks like it was airbrushed and then given a thick coat of gloss varnish.
For the DP's armor, that looks like they went with silver, couple shades of brass, then more silver. Maybe some brown washes/glazes in there somewhere. You could probably get pretty close just by experimenting with drybrushing metallics in different combinations and orders.
Demons need love too...hugs for everyone!
When life gives you lemons, BLOOD FOR THE BLOOD GOD!