Gregor Ferguson of Christchurch asks :-
What is in Lava lamps?
Carmen Drahl, a chemist who works as a reporter with Chemical and Engineering News, responded.
Lava lamp, the trademarked name given by one manufacturer, has become a general name for all liquid motion lamps. The lamps' ingredients are a closely guarded secret but we can look at the general principles.
The shapely lamp houses two main ingredients that are mutually insoluble. According to a U.S. manufacturer, water and wax are the main components of the commercial recipe. The key to the lamp's ever-changing flow is to closely match the density of the wax and water layers. A heat source tweaks the density of one component so that when warm, it is less dense than the other component and so floats to the top. Upon cooling, it is denser than the other component and sinks to the bottom.
Additional agents help the wax gently plume upward instead of breaking apart into bubbles as it is heated and keep wax from sticking to the sides of the container. A patent by liquid motion lamp inventor Edward Walker mentions additives such as dye, mineral oil, carbon tetrachloride, and polyethylene glycol (PEG), but the exact formula of commercial lamps is a trade secret, and there are occasional reformulations.
Many of these additives are dangerous. A 1996 report in a scholarly journal called Annals of Emergency Medicine relays the story of a 65-year-old man who drank the contents of a liquid motion lamp. He spent three months in hospital to recover from kidney damage, with chemical analysis showing it was likely the PEG which caused most damage.
You can learn more about liquid motion lamps' history and view photos of classic lamps at the tribute websites www.flowoflava.com and www.hippielight.com, which are maintained by collector Anthony Vassallo.
Further details on this topic are at Chemical & Engineering News, at http://pubs.acs.org/cen/whatstuff/86/8607sci3.html