Lava lamp

A lava lamp (or astro lamp) is a decorative lamp, invented in 1963 by British entrepreneur Edward Craven Walker the founder of the British lighting company Mathmos. The lamp 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 then placed on a box containing an incandescent light bulb whose heat causes temporary reductions in the density of the wax and surface tension of the liquid. The warmed wax rises through the surrounding liquid, 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. The lamps are designed in a variety of styles and colours. A lava lamp (or astro lamp) is a decorative lamp, invented in 1963 by British entrepreneur Edward Craven Walker the founder of the British lighting company Mathmos. The lamp 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 then placed on a box containing an incandescent light bulb whose heat causes temporary reductions in the density of the wax and surface tension of the liquid. The warmed wax rises through the surrounding liquid, 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. The lamps are designed in a variety of styles and colours. A classic lava lamp contains a standard incandescent or halogen lamp which heats a tall (often tapered) glass bottle. 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.p. 2, line 30 The clear water or mineral oil can optionally be coloured with transparent dyes. Common wax has a density much lower than that of water, and would float on top under any temperature. However, 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. When heated, the wax mixture becomes less dense than the water, because the wax expands more than water when both are heated.p. 1, lines 40 & 45 It also becomes fluid, and blobs of wax ascend to the top of the device where they cool (which increases their density relative to that of the water) and then they descend.p. 1, line 47 A metallic wire coil in the base of the bottle acts as a surface tension breaker to recombine the cooled blobs of wax after they descend. However, lava lamps made in China for the US market since 1970 do not use carbon tetrachloride, because its use was banned that year due to toxicity. The manufacturer (Haggerty) stated that their current formulation is a trade secret. The underlying fluid mechanics phenomenon is a form of Rayleigh–Taylor instability. The bulb is normally 25 to 40 watts. Generally, it will take 45–60 minutes for the wax to warm up enough to form freely rising blobs, when operating the lamp at standard room temperature. It may take as long as 2 to 3 hours if the room is below standard room temperature. Once the wax is molten, the lamp should not be shaken or knocked over or the two fluids may emulsify, and the fluid surrounding the wax blobs will remain cloudy rather than clear. Some recombination will occur as part of the normal cycle of the wax in the container, but the only means to recombine all of the wax is to turn off the lamp and wait a few hours. The wax will settle back down at the bottom, forming one blob once again. Severe cases can require many heat-cool cycles to clear. In 2015, a new design was introduced into the market that uses ferrofluid in place of wax. British entrepreneur Edward Craven-Walker had the idea for the lava lamp in 1963 after watching a homemade egg timer, which was made from a cocktail shaker filled with liquids, as it was bubbling on a stove top in a pub. He hired British inventor David George Smith to develop the device and the chemical formula required put his idea into practice. Smith is credited as the inventor on the original U.S. Patent 3,387,396 for a 'Display Device', that was filed and assigned to Craven-Walker's company in 1965, and subsequently issued in 1968. Craven-Walker's company was named Crestworth and was based in Poole, Dorset, in the United Kingdom. Craven-Walker named the lamp 'Astro' and had variations such as the 'Astro Mini' and the 'Astro Coach' lantern.