Thanks @slinky and @DaveT, appreciate the support
Finished up the Balrog today! Some progress photos first:
Since the last update, I filled in the cracked skin with black, and tidied up various other areas of skin. The legs and forearms were drybrushed.
The tongue was painted in the same way as the flames, as was the whip, however with the whip I only went as far as the orange layer stage, leaving more white so as to show the heat of the whip.
From this stage on, I drybrushed the face/horns and wings with skavenblight dinge to highlight them. Then it was onto all the OSL effects, which I very simply achieved with drybrushing, starting with making a wide radius with orange, then subsequent smaller radii with yellow and white. I tried to hit everywhere it looked like the light from the flames, whip and mouth would hit, including areas such as the feet, the mouth/underneath of the horns, as well as the underneath of the wing that is over the whip.
So, here is the finished piece:
I'm super happy with how it came out! I had been putting it off for a while as it seemed such a big daunting mini to paint, but once I took the plunge and got stuck in it was actually quite straightforward and enjoyable
As always, it's tricky to photograph such a large model and capture how it all looks together as one piece, but I hope you like it!
Yeah Object Source Lighting is the correct term, and to be honest its not as scary as it may seem. Back when I first tried it, on the plastic Frodo that will feature in the Mines of Moria campaign act soon, I applied it using thin glazes, but that took quite a long time. So now all I do is drybrush it on 
I do one stage, then step back and look at it and see if I want to increase the effect radius or intensity, then go at it again, etc.
)
