Hello there!
I hope you all had a good new year!
I recently painted up the Limited Edition Interrogator Chaplain Seraphicus, from the brand new Dark Vengeance Box set. After many requests to begin letting everyone know how I achieve certain effects and techniques, I've decided to upload this short tutorial on my process for painting cloaks! It is apparently, a speciality of mine!
Firstly, let me just talk about my equipment and set up. I use Citadel and Vallejo paints and inks mostly, citadel brushes, citadel primer and either a vallejo glaze medium or the Lahmian Medium also from Citadel. Per stage I had painted around 3 thin layers of each colour, letting completely dry between coats. I follow the general principle of a base layer, ink wash, and a highlight for painting. If and when I deviate from this, I'll explain where and why!

Here goes!
Step one: Base Layer. Warpstone Glow.
Several layers of Warpstone glow, painted evenly over all areas of the cloak.
Step Two: Wash: Anthonian Camoshade
A decent, even coverage of the green ink. Let the ink do the work for you, by process of gravity and whatnot, it will find the natural recesses in the model, and shade them accordingly.
Step Three: Layer: Warpstone Glow
Once the ink has completely dried, you can see the two seperate areas of light and dark shading. Paint over the lightest area, leaving the shaded areas alone. With this step, I typically leave around 50% of the surface shaded.
Step Four: Layer: Warpstone Glow + Warboss Green
Add a very small amount of Warboss green to the warpstone glow, around 1:10 should do it. When painting this layer, notice the painted line between your shading and the last layer of Warpstone glow, and stay within that line. The way I think of this is similar to concentric shapes, over lapping each other, getting smaller each time.
Step Five: Layer: Warpstone Glow + More Warboss Green
I think you're getting the idea by now

A little bit more warboss green mixed into the Warpstone Glow, and at this stage you begin to define the very highest, most prominent edges of the cloak, toward the bottom.
Step Six: Layer: Warboss Green
With a pure warboss green, and staying within the lines of your last layer, build up the colours where you want them to be.
Step Seven: Layer: Warboss Green + Moot Green
For the next layers, add increasing amounts of Moot green, in the same fashion as previous steps.
Step Eight: Edge Highlight: Moot Green + Yriel Yellow
For this layer, I basically painted a very neat, thin line with the yellow/green mix, along the most prominent edge of the cloak. If it looks right, it is right!
Step Nine: Edge Highlight Yriel Yellow
Leaving a small transition between your last highlight, add a line of pure Yriel yellow, extremely carefully, leaving some of the previous yellow/green colour show through.
Step Ten: Final Edge Highlight: Yriel Yellow + Ceramite White
Exactly as before, paint a very neat, tiny white line, within the yriel yellow highlight you painted previously, and BOOM, done!
Here is the finished model!
I don't profess to be the greatest painter of all time, but I'm proud of my abilities and I absolutely love my job. If you have any comments or questions or anything I'd love to hear them, and I hope you learnt something whilst reading this!
The community of you guys is what makes our hobby so great, so genuinely, thank you!
Cheers!
Ian