Very cool. Favourited for refference.
On that note, could you give us a bit of a walkthrough through the painting process?
Let's see. IIRC, the process was something along these lines (I'll use generic terms for the paint shade):
Apply basing material, in this case a medium ballast.
Prime everything (including the base) white, either via spray or brush. The Bones stuff will feel sticky if you spray, but it doesn't hurt the material and vanishes once you get a coat of paint on it.
Basecoat with your brightest yellow (or highlight heavily with it leaving some white showing through, if you're after hotter look).
Highlight with a darker yellow. Repeat with a light orange, than a darker orange. You can pretty much just apply these stages as simple drybrushes, going a little lighter each time. Remember that the darkest part of a flame is actually at the top/coolest area, so you're essentially reversing the more common highlighting technique of starting dark and going lighter with each successive layer.
Do a more controlled highlight with a bright red near the high points of the flame or wherever else you want to emphasize the shape of the model, maybe even add a darker red final highlight.
Carefully pick out the tips of the flames in a thinned dark gray, charcoal, or soft black color for that smoke effect. You can apply a heavier drybrush of same to the coal bed basing, maybe followed by a lighter brush of pure black.
You can vary the look a lot by adjusting how much of each color is left showing at the end. More white and yellow = hotter, more red and darker reds with more smoke highlight = cooler. You could (and I probably will, at some point) play around with non-traditional flame colors using similar techniques and a different pallet. Magical flames could be blue or green or whatever. Tzeentch fans could even do one in shades of pink, yeah?