From the fluff point of view, I would imagine that the Dark Mechanicum does not waste any time on painting their war machines! Instead you see the bare materials that the demon engines are made of. I could imagine that they do not just use boring steel but some special metal alloys that are more durable and hold the chaos energies better. The picture of the Decimator matches this idea, with a metallic color that has some brown and dark blue sea flavors added... In addition, I wanted to add some golden metal for the trim and some glowing runes to emphasize the demonic nature of the Defiler... OK, enough of words, let's go!
1. After the black basecoat, I airbrushed Dark Sea Blue in an inhomogeneous pattern all over the miniature
2. I airbrushed Tin Bitz all over again in a rather inhomogeneous way...
6. I do a wash/glaze of Dark Sea Blue mixed with some Klear Gloss Varnish trying to give the metal a bluish shine, which does not have to be homogeneous.
7. A wash with Brown Ink in the corners and shadowy parts, and including the gold
8. A wash of thinned Bestial Brown only around the rivets and other structures where rust/dust would collect.
10. A wash with Devlan Mud and then Baddab Black mainly to deepen the shadows and take away the shinniness of some metal.
11. Some very careful lining of recesses between moving parts with Black Ink (as a proxy for oil).
12. Drybrushing/Highlighting with Boltgun Metal
15. Putting the glow into the runes with Fiery Orange using the finest lines you manage.
16. Finishing the model (sorry no photos of this part anymore):
- I painted all cables simply in Chaos Black.
- There was a skull that I primed with brown, highlighted with Bleached Bone and then shaded with Devlan Mudd.
- The rockets in the Havoc Launcher got a red tip and the sensor in the launcher itself were also painted red.
- I added some blood (Tamiya Clear Red) to the claws and spikes, just a bit...
- I wanted a crackling lightning effect on the power scourge in blue. So I first drybrushed parts of it in white and the put craeful glazes osf Enchanted Blue. Finally I tried to draw some little lightnings with white again. However, I did not like the result and so carefully airbrushed some additional white onto the tip of the scourge before I applied again some glazes of Enchanted Blue trying to simulate an inner glow (i.e. more blue towards the edges). I am not completely happy with the result but it is OK.
Still, I am not 100 per cent happy with the result because the metal became to dominating, i.e. the blue and brown are not strong enough anymore. Therefore, people might just think that it is an Iron Warriors Defiler on first glance... Well, I will try to improve the color scheme on my next model...