Ben Saunders:
I hope it’s ok to post tutorials from elsewhere on the web here…
I’m not that keen on lava bases myself, but I just found this tutorial from EonsOfBattle:
http://www.youtube.com/watch?v=ZciGyq0e3F4
He uses egg shell, which wouldn’t have occurred to me. I do like the final effect, but I’m not sure how practical it is.