lava lamp
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decorative lamp with container of bolus in clear liquid, which heats up at the bottom and rises before cooling and falling back to the bottom
~7 min read
Encyclopedic overview
Lava lamps An original Mathmos Astro lava lamp A lava lamp is a decorative lamp that was invented in 1963 by British entrepreneur Edward Craven Walker, the founder of the lighting company Mathmos.
Lava lamps consist of a bolus of wax and a clear or translucent liquid inside a glass vessel. The vessel is placed on a lamp base with an incandescent light bulb. The 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. The lamps are designed in a variety of styles and colours.
Excerpted from Wikipedia’s “lava lamp” article, available under the CC BY-SA 4.0 licence.