First up, the final effect achieved with this technique.
I used a Badger Renegade Krome airbrush with a 0.2 mm nozzle for this model. Any airbrush will work, but to shade in this manner you really need fairly fine control.
-Citadel Averland Sunset (any golden yellow with good coverage would work)
-Vallejo model air Yellow (any bright yellow would work)
-Vallejo model air Sandy Brown (any light reddish brown is fine)
-Vallejo model air Burnt Umber (reddish brown)
-white (I used old Citadel skull white)
-white or light grey primer
This is one technique for airbrushing power armour. Here are some other links showing this technique and others. At From the Warp, Ron shows how to paint power armoured models using spray paint to paint zenithal highlights. Here are the links to his Dark Angels, Word Bearers, and Ultramarines. There is a fantastic tutorial on airbrushing grek knights with zenithal highlights on dakka dakka. Finally, BuyPainted has some excellent youTube videos showing these techniques, including this excellent one on how to paint Krannon from Dark Vengeance.
Step 1-Prime and prepare the model
I primed the model using vallejo white primer using my airbrush. I was careful to get a light coat. I used white as it would be easier to get good coverage with yellow afterwards. Not that I painted the arms and body separately so I could more easily reach the whole model. I pinned the model to a block and attached the arms to some plastic rod to make painting easier.
Step 2-Base coat model Golden Yellow
I base coated the entire model in Citadel Averland Sunset. I used the Citadel base colour as it has good coverage. I thinned it a lot using airbrush thinner. It still clogged my airbrush a lot. If you can find a nice golden yellow that clogs less, use it (and tell me which one!). Airbrushing this base coat took under five minutes. To get a similarly even coat of yellow painted by hand would take a long time.
Step 2-First shadows
I then painted the first shadows in using VMA Sandy Brown. Don't worry if you paint a slightly larger area than you want. We will clean that up later on. Paint shadows at the edge or armour plates, the inside of the legs, recesses and other areas where light would not reach as much and where you want a final shadow. Spray the light brown fairly lightly so the yellow still shows through a little.
Step 3-Second shadows
Next, I painted the deep, dark shadows using VMA Burnt Umber. You want to be careful to just get the dark brown into the deep recesses and places you want dark as it is more difficult to cover later.
Step 4-First highlights
As I had oversprayed the shadows a bit I brought back some of the base colours by airbrushing Citadel Averland Sunet. I focussed on painting the center of places like the knees and getting highlights as if there was a light source above. You can see how I lightened up the knee pads, top of helmet, cod piece and toes.
Step 5-Second highlights
I then added more armour highlights using VMA Yellow. I highlighted areas I had lightened in the previous step. I focussed on letting the paint dry between applications so it did not pool. The yellow is really transparent, so you have to be really careful to not apply too much at once. I used zenithal highlighting a bit on the face by applying the paint from directly above.
Step 6-Line highlights
I finished the armour by quickly adding light line highlights around the face and prominent edges. I used a mix of skull white and VMA yellow to ensure they blended well. This really helps the face to pop. I focussed these on the top of the model to avoid unnatural highlights on the lower parts of the model. In my opinion, we want to use these light line highlights to draw focus to the face.
I then painted the rest of the model using a brush. Most of the details simply got a basecoat, wash with Devlan Mud, and the highlighted again with the base colour. I used Bleached Bone for white areas, VMA Gun Metal for metal, and new Citadel Mephiston Red for the red areas. I darkened a few shadows in the face and around the hands using a light glaze of Devlan Mud. I based the model by airbrushing Vallejo Model Air Dark Earth and then dry brushing bleached bone over it before adding some grass and snow. I lightly airbrushed the lower legs with VMA Dark Earth to create a bit of light weathering and dust. I added the decal and blended it into the shoulder pad by airbrushing VMA Dark Earth over the lower parts of the decal.
Speeding it up
There are a number of ways you could speed up this process for tabletop quality models. Instead of painting each shadow and highlight individually you could simply use zenithal techniques to spray highlights over a brown base coat. For example, spraying Burnt Umber on the whole model then focussing the two yellows from above. You could also reduce the colours used by only spraying Averland Sunset, VMA yellow, and VMA Burnt Umber. By batch painting models you could quickly finish the power armour on a squad in an hour or two once you get the process down.
Thanks for reading. Let me know if you found this useful. I would love to see some pictures of this technique being used on your models.