Lava lamps and oil wheels

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Lava lamp

A lava lamp contains two things with very similar density(/specific gravity[1]), typically one of them solid(ish) at room temperature, often an oil or wax.

That wax will have higher density when cold, but the density lowers faster than the liquid, so will start floating, until it cools down and become higher density again and fall.


While the basic mechanics are fairly simple to understand, it's hard to find two specific substances with the right properties: very similar density, something that coalesces, is dyeable, melts at the right temperature (often the light source is also the heat source), safe in terms of flammability and toxicity, etc.


Additionally, the relation of densities also need to be tuned to the amount of heat being added. Since the lava effect is a thermal (im)balance, too hot and the wax will float just. This means DIYing will always involve trial, error, and patience.

You may want a hydrometer[2] when tuning.


You also want any small separated globs to be able not stay separated forever. Chemical properties help, but it's also part of the reason various lava lamps have a spring at the bottom.


Also, since it's a lot of trouble, you may just buy one after all.


Ingredients

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

There are a number of variations and common ingredients.


Alcohol (like denatured alcohol) and wax works well, but something that flammable is sort of a bad idea safetywise.


It seems that in many cases it's (distilled) water, and a wax (or oil) with a density near it.

The harder part is to get a wax and water of similar enough density.

You can add a little (isopropyl) alcohol. Isopropyl and water mix at any concentration, lowering the density, making it an easy way to fine-tune the density for your choice of wax.


The wax was historically mixed with carbon tetrachloride[3] to tweak its density to sink in water, but not anymore due to its toxicity.

These days, trichloroethylene (a solvent) is another option. It's also sort of nasty, though, keep that in mind when mixing it.

DIY tweaking the densities is a bit trial and error.






Depending on the actual ingredients, shaking may create a mess of small bubbles that may not coalesce, though it may sometimes resolve itself after you cool the thing down, once or a few times.

A little bit of hydrophobicity helps here. Many paint solvents will work. Apparently dishwasher soap may too.(verify)


Coloring

Basically, water-based coloring for water, oil-based dyes for the oil/wax.

To some degree you can count on the dye's properties to not mix with the other liquid. ...but you might need to experiment with oil dyes to find one that mixes properly with your oil.


For water, food coloring works, things like printer ink might too.

For oil and wax, I'd say experiment with variants of candle dye.


On heat

Lava lamps tend to have incandescent bulbs as both a light and heat source.

Commercial lava lamps may have heat spreaders (metal rings and such) on the bottom to try to heat the bottom more equally and avoid permanently .


The amount of heat you'll need depends on the container size, and is one of the things you'll probably want to tweak to get a nice and balanced effect.


More heat tends to mean bigger clumps, and going up higher.

If the blobs stay at the top, use a smaller bulb, use a dimmer, or perhaps a small cooling fan on top.



You may like a dimmer, both to control behaviour and to allow different bulb power.

See also

Oil wheels

Think seventies-ish psychedelic light show projections.

There are various completely different ways to do light shows, Oil wheels in some sort of projectors are one of them.


Oil wheels can contain various things, but are similar to lava lamps in that it's two liquids that don't want to mix.

It's different from lava lamps in that the temperature is lower, the wheel itself is thinner, you don't want it to coalesce too easily, so people generally settle on something like colored oil (rather than wax) and colored water. Glycerol instead of water also works(verify)

The oil can be mineral oil (e.g. baby oil), paraffin oil (think lamp oil), or similar, and can be colored with e.g. liquid candle dye.

You probably want less of the denser stuff.


The wheels themselves can be plexiglass or similar glued together (typically with some sort of spacers - you don't need/want much space, and it helps if the distance is consistent). Three layers mean you can have two independent color sets interact.