I searched for lava lamps i only found lamps which was necessary put alka-seltzer to work, what i consider a fake lava lamp.
Me and my colleague have decided do the same project and make an instructable, he posted the project 1st and he got all the profit xD.
What you need is:
an aluminum can
a colorless glass bottle
2 BOTTLES OF ALCOHOL
Step 1: Preparing the bottle
Put a few drops of colorant in the alcohol and shake (I used red)
Put the oil in the bottle (isn't necessary paint it)
fill the bottle with the already painted alcohol and go adding water when the oil rise, stop there.
close the bottle (I noticed when the lamp warms a lot content in the bottle tends to rise out of the bottle, so i recommend don't fill up at max)