Here is one of my older works. C&C welcome.
Full Size : Lava Lamps
Looks okay, the only thing that gets me is the blackness of the transparent part of the lamp itself. Perhaps your raydepth is a little low.
delete…
Think of a real lava lamp- does it have just one blob?
Add some metaballs inside of the lamp and form them in the shape of several different globs- it will improve this immensely.
I think this looks excellent! But some of the others are right, the one “lava ball” cuts down on the realism while the glass (black part) should be adjusted just a hair. Otherwise, I think it’s gorgeous! Bravo!