Last stage before pigments.
I used a Citadel Drybrush paint for the exposed metal areas- very easy and quick to use. I believe AMMO do a similar range. It looks way too shiny here and it’s not that noticeable on the real thing but several pigment coats will knock the sheen off considerably.
As well as using the Citadel paint I put a dark brown and a black acrylic wash in random places to add a bit of variety.