WOW! i am such a fan of your work! Every piece is a masterpiece! May I pick your brain for some advice? I'm stumped on red heads and brunettes.... What did you do for the brunette top center and auburn on the right? Just magnificent!
Well, for the red head I used a base coat of VMC Cavalry Brown and layered up highlights with GW Jokaero Orange and then added a bit of VMC Yellow Ochre.
The brown hair had a base coat of VGC Charred Brown and was highlighted with VGC Beasty Brown and then whatever happened to be on my palette that was still wet at the time...

could have been VGC Desert yellow or VMC US Field Drab, just some sort of tan brown.
Hope that helps.

Thanks for the comments everyone.
