A lava lamp is a novelty light that contains blobs of colored wax inside a glass vessel filled with clear liquid. The wax rises and falls as its density changes due to heating from an incandescent light bulb underneath the vessel. Briton Edward Craven-Walker invented the lava lamp in 1963; it was originally called the ‘Astro Lamp.’
The wax is transparent, translucent or opaque mix of mineral oil, paraffin wax and carbon tetrachloride. The density of common wax is much lower than that of water and would float on top under any temperature. However, the carbon tetrachloride is heavier than water (also nonflammable and miscible with wax), and is added to the wax to make its density at room temperature slightly higher than that of the water.
The Daily Omnivore 