Thanks for all the comments guys.
To make the lava base :
1 - File a base slightly with sandpaper until it's smooth.
2 - bake a lump of Sculpey and, when hard and cool, attack it with a hammer and screwdriver, carve lumps out of it until it's as rough as you want it to be then glue to the base.
3 - take a Space Marine or two and carve of the little knob off his back where his powerplant/backpack attaches and glue these on the base to represent bubbles
4 - paint the base to represent lava (black through red to orange then yellow and finally white)
5 - paint the bubbles with thick paint and let it run down the sides this will give a nice flowing shape to the bubbles coming up from the base also make sure the bubbles are painted up to white.
6 - paint the rock as you want it.
7 - work out where the light from the lava is going to strike the rock and the drybrush with the deepest red you've got then drybrush progressively lighter shades in a smaller area until you are using roughly 50:50 yellow/orange mix. Never go up to white it doesn't look right and try to avoid using blood red for some reason it doesn't look right either.
8 - give the rock a very thin glaze with black ink to tie the rock and light reflections together.
9 - jobs finished.
it's a very nice model... just i don't understand the daemonette...
Daemonhunter / Daemonette, seemed logical to me