Product information A lava lamp is a novelty item typically used for decoration and ambiance rather than illumination; the slow albeit chaotic rise and fall of the randomly-shaped blobs of wax is fancifully suggestive of the flow of lava, hence the name. The lamps are available with a wide variety of container styles and colors of wax and liquid. They rose to prominence in the late 1960s and early 1970s and are often associated with the hippie movement of that period. The lamp consists of an incandescent bulb which heats the contents of a tapered glass bottle containing water and a translucent mix of wax and carbon tetrachloride (although other combinations may be used). A metallic wire coil which is hidden in the base of the lamp both furthers the necessary heat convection and suspends the falling blobs of liquid wax. The wax is slightly denser than the water at room temperature, and slightly less dense than the water under marginally warmer conditions. This occurs because the wax expands more than the water when both are heated. Since common wax is much less dense than water and would float at any room temperature, a heavy, nonflammable solvent is added to adjust the wax density to be slightly higher than that of water. A lava lamp may take 2 to 3 hours to warm up and stabilize. Accelerated heating by other means, or shaking the lamp may cause permanent damage to the aesthetics, or the look of the lamp. Care should be taken to avoid personal injury, as the glass and the area close to the light bulb are normally very hot. Wax at the bottom heats until it melts, eventually becoming less dense than the liquid around it. Portions of wax thus overcome their surface tension and rise. Near the top away from the heat source, the wax cools and contracts. Its density thus increases, and the wax falls to the bottom, only to be reheated again. This cycle repeats itself for as long as the light bulb stays on and supplies the heat. Lamps are designed to work best at typical ambient room temperatures of 22 °C (72 °F), +/- 6°C, but will still function outside this range. The lava lamp owes its classic shape to physics as much as aesthetics: at the tapered end there is more surface area per unit volume of liquid, hence the liquid in that area undergoes a higher rate of cooling than the liquid nearer the bottom. The whole process is a macroscopic, visible, form of convection heat transfer, although it also occurs on a molecular scale within the liquids themselves. The difference in temperature between the top and bottom of the lava lamp, as with a Galilean thermometer, is only a few degrees. While the fluctuating wax spheroids frequently collide as they rise and fall, they do not cohere in transit insofar as they regain sufficient surface tension. The heat source at the bottom, most specifically the heat coil, overcomes surface tension of the individual wax blobs. This causes the descending individual blobs of wax to coalesce into the single liquid wax mass at the bottom of the container. The cycle of rising and falling masses of colorful wax continues for as long as the temperature differential remains sufficiently great. 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 virtually all of it rising to the top (too hot). Sensitivity to initial conditions renders the manifold characteristics of the wax blobs (their phase shifts, size, speed, number, currents, protean forms, varying viscosity, collisions, etc.) sufficiently unpredictable to serve as an excellent if fanciful example of chaos theory in action. The Lavarand system used this unpredictability as the basis of a notable hardware random number generator.   Photos