Metallic NMM?

Here's a guide to metallic non-metallic metal. It sounds stupid and it works.

Paint it black.

Really thin out your Leadbelcher, and go over the flats, leave the black in the recessed areas.

Now hit it with a good coat of Drakenhof Nightshade. It's hard to see, but the blue does make a difference.  

Break out the Runefang Steel and do your edge highlights. 

Finally, one simply considers where the light source is (as for NMM) and work up the highlights and such. Carefully bring things down with thin Leadbelcher and Nuln oil. 

Don't forget to stop when you're happy. If you want to add rust very, very, carefully go in with Troll Slayer Orange, and Fire Dragon Bright. As with many techniques, sometimes less is more. 

FFWD four steps, paint a shield, make a mannequin, and tada, the Grots have the beginnings of a quintain.

DMGWLFP...