A few washes airbrushed from below where shadows would be... red (carroburg crimson - citadel), sepia (seraphim sepia - citadel) and brown (dark brown wash - vallejo), all thinned more than normal using airbrush thinner. Then a lighter skin tone, the barbarian skin by itself, super thinned down with airbrush thinner... probably 5 parts wash to 1 part paint, airbrushed form above. I think the shadow and highlight pass definitely added volume.
1 attached image. Click to enlarge.