Lava lamp

It consists of a bolus of a special coloured wax mixture inside a glass vessel, the remainder of which contains clear or translucent liquid.

The vessel is placed on a base containing an incandescent light bulb whose heat causes temporary reductions in the wax's density and the liquid's surface tension.

As the warmed wax rises through the liquid, it cools, loses its buoyancy, and falls back to the bottom of the vessel in a cycle that is visually suggestive of pāhoehoe lava, hence the name.

A formula from a 1968 US patent consisted of water and a transparent, translucent, or opaque mix of mineral oil, paraffin wax, and carbon tetrachloride.[3]p.

1, line 47 A metallic wire coil in the bottle's base breaks the cooled blobs' surface tension, allowing them to recombine.

[7] British entrepreneur Edward Craven Walker had the idea for the lava lamp in 1963 after watching a homemade egg timer, made from a cocktail shaker filled with liquids, as it bubbled on a stovetop in a pub.

[9] Craven Walker hired British inventor David George Smith to develop the device and the chemical formula it required.

Smith is credited as the inventor on the original U.S. patent 3,387,396 for a "Display Device" filed and assigned to Craven-Walker's company in 1965, and subsequently issued in 1968.