(Unless otherwise stated, all colour references are Citadel/GW.)
To be honest, I had already spent hours converting the bugger, which had been standing on my desk for months (which certainly doesn't show when you read the article). And I was sort of getting impatient, which meant that I wasn't going to take my smallest brush and most watered-down colours to paint him up... if you see what I mean (yeah, you do).
After priming the model black, I decided to drybrush the skin. The relief on the large model was sharp enough to make good use of that technique. Oddly enough, though, there were some areas that would just look too flat if I used it exclusively.
Drybrushing is a very paint-consuming technique, so you've got to think about it twice before you go. I put a generous amount of undiluted Scab Red paint on my brush, and started with the most exposed areas. When the brush was getting drier, I used it where the actual drybrushing was required, so that there was no waste of paint, and the coat would be most solid where it's most exposed.
Then I did the same using Prince August Carmine Red, which lightened the skin quite a bit. I toned it down with a black wash, and redid the Carmine Red drybrushing. Then I painted it properly with diluted PA Carmine Red, drawing thin lines where I felt some texture had to be created in order for the skin not to look too flat. I finished the skin with touches of Blood Red on the most exposed areas, and within the PA Carmine Red lines I had painted.
Most of the details to pick up were on the face. For the teeth and the bone in his nose, I used a basecoat of Scorched Brown, then Bleached Bone, and finally, Skull White. The gum was simply painted in Warlock Purple, and then in Tentacle Pink.
The metal casing on the left side was done using Boltgun Metal and Mithril Silver.
It was when I wanted to paint the bionic eye that I realised I had forgotten something: the eye was just a hole an empty hole. I should have filled its bottom to get a flat surface to paint the optic on. Rather than using greenstuff, which would have taken too long, I used Araldite I simply put a small drop in the eye. It dried quickly, so I could paint it Dark Angels Green, and highlight it with Goblin Green.
The tongue was painted with Liche Purple; this is a good example of how I like to do most of my highlighting work on a black undercoat. First, I try to get several shades of the same colour using one, just by watering down the paint more or less, then I just do a few layers more with more and more white in the mix. So I first applied a very thinned layer of Liche Purple on all the tongue. Then I applied the same colour with less water in the mix in the exposed areas (i.e., I left the middle untouched), then I applied a solid, hardly diluted layer on the areas that show most. Then I did the more conventional highlighting work, and drew thin vertical lines on the tongue, using more and more white in the mix, using well-diluted, "milky" paint. It doesn't take much time and works rather fine, I think.
For the horns, I used more or less a mix of the same simple techniques I've just described. I drew lines from the inside to the point of the horns, with less and less thinned Codex Grey, then I did the same using Skull White. Didn't take very long either, and it looks fairly decent.
For the other parts in black, I proceeded differently. The trousers were flat, as I sculpted no detail/texture on them ; when that happens, you basically have to paint the texture on. I did it roughly, I must admit, using soft drybrushing with Codex Grey and Skull White; then I drew lines in the same colours. I finished the job with a simple Chaos Black wash, and an extra Skull White highlight.
I did the same for the rotary-plasma-cannon-from-gothic-hell's body, except I painted the rotating part by drybrushing it Brazen Brass, then giving it a Brown Ink wash, then another Brazen Brass drybrushing. To give it a 'plasma weapon' look, I painted the tubes around it Regal Blue, and progressively highlighted it by adding white to the mix.
Finally, the loincloth. I painted a solid coat of Bleached Bone on a first coat of Scorched Brown, leaving it showing through in the deepest recesses; then I simply highlighted it by adding more and more white to the mix.