Whats in a lava lamp?

Question

I have an old lava lamp from somewhere in the late 60's early 70's. Basicly its old! but still works. Through the years some of the liquid in this lamp has been spilt and I was told that I can fill it up with water. Now I thought they were filled with some kind of oil. When I said this to my friend he then told me that the newer ones do have oil but the older ones from the same time has mine were made different and that they were filled with water.

Is this true?

Answer 1

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A lava lamp is a novelty item typically used for decoration rather than illumination. The gentle flow of randomly-shaped blobs of wax suggests the flowing of lava. The lamps are available with a wide variety of container styles and colors of wax and liquid.

The lamp consists of an illuminating bulb, a glass bottle containing a transparent oil and translucent wax (although other combinations may be used), and a metallic wire coil. The glass bottle sits on top of the bulb, which heats its contents. The metallic wire coil is hidden in the base of the lamp, on which the glass bottle is sitting.

The wax is slightly denser than the oil at room temperature, and slightly less dense than the oil under marginally warmer conditions. This happens because the wax expands more than the oil when heated.

When the lava lamp is turned on, the light bulb heats the bottom of the glass bottle and the metallic wire coil, which in turn heats the contents of the glass bottle in this vicinity.

Wax at the bottom heats until it melts, and eventually becomes less dense than the liquid above it. At this time, a portion of the wax rises towards the top of the container. Near the top, away from the heat source, the wax cools, contracts, and as its density increases it begins to fall through the liquid towards the bottom of the container again. This is a macroscopic, visible form of convection heat transfer, although it also occurs on a molecular scale within the liquid itself. The difference in temperature between the top and bottom of the globe is only a few degrees.

One mass of wax may rise as another falls. The metal coil at the bottom helps to overcome the surface tension of the individual wax droplets, causing the descending blobs to coalesce into a single molten wax mass at the bottom of the container. The cycle of rising and falling wax droplets continues so long as the bottom of the container remains warm and the top of the container remains cool. Operating temperatures of lava lamps vary, but are normally around 60 °C (140 °F). If too low or too high a wattage bulb is used in the base, the "lava" ceases to circulate, either remaining quiescent at the bottom (too cold) or all rising to the top (too hot). Lava lamps are possible to overheat and are usually supposed to be used in a 4-8 hour period based upon size. There have been cases in which lava lamps have exploaded because put on an oven stove.

Chaotic behavior makes the movement of the wax unpredictable—hence lava lamps can be used as a physical random number generator.

Answer 2

Lava-type lamps can be made with water mixed with isopropyl alcohol as one phase and mineral oil as the other. Other materials, which may be used as oil phase ingredients include benzyl alcohol, cinnamyl alcohol, diethyl phthalate, and ethyl salicylate.

Other additives
Other additives used in lava lamp fluids include various oil and water-soluble colorants. The specific gravity of the aqueous phase can be adjusted through the addition of sodium chloride or similar materials. In addition, a hydrophobic solvent may be added to the mixture to help the lava coalesce. Turpentine and similar paint solvents are said to work well in this regard. Antifreeze ingredients can also be added to increase the rate at which the lava warms.

Answer 3

Really hot wax.