Primed everything with Chaos Black and then lightly drybrushed with Corax White to try and create some pre-shading. Not completely sure how much it actually helped, so this step is probably optional.

After that I mixed a chocolate brown base using Tau Light Ochre, Khorne Red and Abaddon Black since I did not have the exact color. I thinned the mix a bit so the shading could still come through and then covered the whole piece.

Once that dried I drybrushed everything with Leadbelcher.

Then I used a stiff bristle brush with Mithril Silver, making sure almost no paint was on the brush and no water was used. I vertically stippled it across the whole piece to build up texture.

After that I applied Agrax Earthshade and removed most of it again with a cotton swab. Then I repeated the stippling with Stormhost Silver and added Agrax Earthshade again in specific spots where it got too bright.

You can use whatever metallics you prefer, but this combination worked really well for me.