To take this technique to the next level and really make the lava glow, use fluorescent yellow, orange and red instead of standard hobby colors.
The "reverse drybrush" (light to dark) paint sequence is
white primer
fluorescent yellow
fluorescent orange
fluorescent red
normal red
dark red
dark gray
black
This is the first piece I ever did using this technique: http://www.armorcast.com/terraform/picture/461l.jpg
Photo ain't great and does not really show how well it glows, but Steve Jackson picked it up at a GAMA show, looking for the light source underneath....
tim