Like most things having to do with lava, the official United States patent is a thing of uncertainty. For many years, we've been told that the US Patent for lava lamps was patent #3,570,156 of March 16, 1971. But recently we've come across a very, very convincing document from 1July 11, 1968 showing US Patent #3,387,396. Read on!
US Patent #3,570,156
Although this type of motion lamp was invented in 1963 by Edward Craven Walker, and patented in England by his company in 1964, this US Patent dates to March 16, 1971. (Can you believe 8 years passed before the lamp was patented in the States?)
Of course, the patent itself is vague concerning proportions of ingredients. The lava component is said to consist of "a solidified globule of mineral oil such as Ondina 17 (R.T.M.) with a light paraffin, carbon tetrachloride, a dye and paraffin wax."
The clear liquid is roughly 70/30% (by volume) water and a liquid which will raise the coefficient of cubic thermal expansion and encourage the movement. The patent recommends slip agents such as propylene glycol for this. However, glycerol, ethylene glycol, and polyethylene glycol (aka PEG) are also mentioned as being sufficient. May did some research of these chemicals and found that these aren't cheap. The best prices she found are at VWR Scientific Products where 500ML of propylene glycol is 10.75 plus shipping. We never tried this formula (it seemed over our heads).
US Patent #3,387,396
Submitted by David George Smith of London on behalf of Craven Walker's Crestworh Company. The patent falls under Display Devices. The Abstract of the Disclosure reads, "A display device comprising a container having two substances therein, with one of the substances being of a heavier specific gravity and immiscible with the other substance, with the first substance being of such a nature that it is either substantially solid at room temperature or is so viscous at room temperature that neither will emulsify with the other liquid, and when heat is applied to the container, the first substance will become flowable and move about in the other substance.
...The liquid in which the globule is suspended is usually dyed water, but not necessarily so. The other liquid is chosen with very many considerations in mind, including the relative densities of the liquids at the desired operating temperature; the fact that the liquids must be immiscible; the fact that the surface tension must be such that the globule does not adhere to the walls of the container; the relative coefficients of thermal expansion of the liquids; and the shapes that are obtained during operation. A suitable liquid for the globule has been found to comprise mineral oil, paraffin, carbon tetrachloride and a dye or dyes. However, undue shaking or sharp impacts, especially during transport of the display device, can cause total or partial emulsification of the globule."
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