How Does a Lava Lamp Work?

A reflection of a lava lamp. — Lava lamps look cool and complicated, but the science behind them isn't all that complex. Jamey Coles Photography / Getty Images

Liquid motion lamps (which most people know as "lava lamps") have been around for decades. The theory behind a liquid motion lamp goes something like this:

In the lamp you have two liquids which are:

Very close in density
Insoluble in one another

Oil and water are insoluble in one another (that's where the expression "oil and water don't mix" comes from), but oil and water have very different densities (a volume of water weighs a lot more than the same volume of oil). They won't work, so you search to find two liquids that are very close in density and are insoluble. This site can help you in that search.

Now you apply heat to the bottom of the mixture. In a liquid motion lamp, the heat usually comes from a light bulb. The heavier liquid absorbs the heat, and as it heats up, it expands. As it expands it becomes less dense. Because the liquids have very similar densities, the formerly heavier liquid is suddenly lighter than the other liquid, so it rises. As it rises, it cools, making it denser and therefore heavier, so it sinks.

This all happens in slow motion because heat absorption and dissipation are fairly slow processes, and the density changes we are discussing here are very slight.

Here are some interesting links:

Originally Published: Apr 1, 2000

Lava Lamps FAQs

Can I leave my lava lamp on all the time?

It is not recommended that you do, to avoid overheating the wax. Lava lamps should be turned off after about eight to 10 hours.

Can I make a lava lamp at home?

Yes, it can be a fun experiment. Add two tablespoons of baking soda to an empty mason jar. Then add some oil to it. Next, take another jar, pour in some vinegar and mix in a couple drops of food coloring. Use a dropper to take some of this mixture and add it to the jar with the oil. Watch the magic happen!

What is inside a lava lamp?

The swirling "lava" is made of wax, the density of which is increased by adding compounds such as carbon tetrachloride. The liquid is either mineral oil or water, sometimes enhanced with glitter or coloring.

What will happen if I shake a lava lamp?

Lava lamps should not be shaken while warm. The liquid can turn murky and the lava might break. In case this happens, switch off the lamp and wait at least 24 hours to turn it back on.