# Liquid that looks like smoke when bottled?

I am making a gift that will consist of a liquid in a sealed bottle. I want the liquid to have a magical appearance. Something like the appearance of smoke - varying opacity from almost clear to almost opaque but never completely mixing. I am looking for a liquid or combination of liquids with the following properties:

• Looks like smoke
• Will not become homogeneously opaque over a relatively long period of time (months)
• Non-toxic and non-reactive in a household setting (in case it is spilled accidentally)
• Can be coloured would be a bonus
• Play nethack and look for "a smoky potion" ;-) To be serious again, it is unclear what do you expect this to look like? In my mind, it would have some movement involved. – Gyro Gearloose Jan 22 '16 at 17:58
• Welcome to Chemistry.SE! If I understand, you want something that has two mixed liquids that don't separate, give a "smoky" look and neither separate or become completely opaque. Cool idea, but sounds tricky even without your other criteria. – Geoff Hutchison Jan 22 '16 at 19:13
• It seems to me that rheoscopic fluids may be a close fit to the requirements. – Nicolau Saker Neto Jan 22 '16 at 23:03
• Yes, rheoscopic fluids is very close to what I am looking for. Thank you! – Chris Jan 23 '16 at 0:52

So you want to make something that looks like smoke. What makes smoke look the way it does, anyway?

Smoke is composed of extremely fine particles, often below $\mathrm{1\ µm = 0.001\ mm}$ in diameter (check here for comparisons with other particulate materials). These particles are large enough to scatter light, which allows them to be seen, but small enough to be extremely light and stay aloft with even very weak currents in air or liquids.

One interesting and very beautiful consequence of these combined properties is that they can clearly reveal fluid flows, which is what gives smoke its wispy, delicate and complex appearance. That's what fluid flows are like all the time, we just almost never have a direct view of it.

So fundamentally your request is quite simple; all you need is a common, non-toxic source of very fine particulate. Fortunately there are good ways to achieve this in practice.

One of the most popular seems to be using fine mica dust. These non-toxic silicate minerals can be ground to form tiny, almost perfectly smooth crystalline sheets. When the particles align properly, light is reflected into a viewer's eyes giving a shiny, glittery appearance. If the mica dust is suspending in a liquid, then the many millions of particles twinkle momentarily as they tumble chaotically under the action of currents in the fluid.

Liquid mixtures containing similar materials are called rheoscopic fluids. There are many many sources online for ready-made fluids, or you can make your own from mica powder or other fine solids. Suspensions in water eventually settle, but last for a long time without degradation, needing only a shake to awaken. With a myriad of water-soluble dyes at your disposal, you can adjust the fluid to the desired colour.

Though rheoscopic fluids based on water and mica are non-toxic and quite safe, that doesn't mean they pose no hazard whatsoever. Very fine particulate can be an irritant if inhaled or exposed to eyes and mucous membranes (especially a problem if handing the dry powder). Just take a bit of care and you can have fun too! Try putting the fluid on a warm surface and see the convection currents!

Not really sure what you're looking for, but it sounds like you want to make something with liquids that have different densities and do not mix well.

You can find these DIY projects by searching for "ocean in a bottle" or "galaxy in a bottle." You can make them by adding food coloring, water and mineral oil to a bottle. For a "magical" appearance, you can add bath products that contain a pearlescent shine, like shampoo, or add glitter.

• This is really more appropriate as a comment rather than an answer. It doesn't really provide an answer to the question. – bon Jan 22 '16 at 22:44