this is a bit dodgy as that are Patented by Matmos in Poole - So don't come crying to me if you get busted.
Use mineral oil as the lava. - To dye the lava, use an oil-based dye like artists' oil paints or a chopped-up sharpie marker.
Use 90% isopropyl alcohol (which most drugstores can easily order) and 70% isopropyl alcohol (grocery-store rubbing alcohol) for the other ingredient. In 90% alcohol the mineral oil will sink to the bottom; slowly add the 70% alcohol (gently mixing all the while; take your time) until the oil seems lighter and is about to "jump" off the bottom.
The correct ratio should be about 6 parts of the 90% isopropyl to 13 parts of the 70% isopropyl.
Use the two alcohols to adjust the responsiveness of the "lava." This mixture is placed in a closed container (the "lava lamp shape" is not required, although something fairly tall is good) ( A whiskey bottle is a good suggestion ) and situated over a 40-watt bulb.If the "lava" tends to collect at the top, try putting a dimmer on the bulb,or a fan at the top of the container. To dye the liquid around it, use food coloring.
Two suggestions for better performance:
1) Agitation will tend to make the mineral oil form small bubbles unlike the large blobs we're all used to. The addition of a hydrophobic solvent to the mixture will help the lava coalesce. Turpentine and other paint solvents work well. To make sure what you use is hydrophobic, put some on your hand and run a little water on it. If the water beads, it should work fine.
2) For faster warm-up time, add some antifreeze or (I've not tried it) liquid soap. Too much will cloud the alcohol. Keep in mind that the addition of these chemicals may necessitate your readjusting the 90% to 70% alcohol mixture.
A diagramy thing
Please note ; if you somhow manage to burn/poison/maim/kill yourself in any way - I bear no responsibilty, in fact I don't even know anything about this web site !!!
PS : I've recieved emails asking if a more powerful bulb will make it bubble faster - yes but it will separate and be unusable very fast.
Also note that Lava lamp cost about £ 40 to £ 150 in the UK and slightly less in the US so if your materials cost more than this it might
be an idea to just buy one. If anybody wants to get a proper one and can't then email me and I will pass one any info I have.