What is a dense/heavy transparant oil or inert/safe non-water-based liquid?

July 18, 2008 4:28 PM

I need a crystal-clear transparent liquid that is as heavy (dense) or heavier than water, not dangerous, and not difficult to obtain. The heavier the better. The catch - it can't be water-based.

I'm trying to suspend (or at least swirl) a non-soluble coloured powder in a liquid as part of a gift, but I can't use water as this will react with and ruin the powder over time. Oils preserve the powder nicely, but the density of the two that I've tried (baby oil, and liquid paraffin) is too low - they are too light to float the powder for very long and so it settles to the bottom fairly quickly. I can't choose a lighter or more durable powder either, so I'm looking for a heavier liquid.

This list of the density of 150 liquids helps a little, but I don't recognize (by chemical name) most of the liquids, even though some I might already have around the house, so I was wondering if you have any insights.

As with water, reactive chemicals like acid will ruin the powder. (Also, acids are a too much of an irritant/danger to want to put into a gift)

I'm hoping for something I could buy at the local department store or hardware store. I don't really want to order something from a specialist or chemical supplier.

Realistically, I suspect my best bet is a heavy but transparent oil, so it probably won't even be as dense as water, but at least something denser than baby oil. Any idea what that might be?

And if you were wondering, it turns out that paraffin floats on baby oil :-)

posted by -harlequin- to science & nature (23 comments total)

Glycerin.

That is your money. It fits the bill methinks.
posted by milqman at 4:37 PM on July 18, 2008 [1 favorite has favorites]

Mineral oil is another possibility. You can most likely buy it in your local pharmacy (right beside the glycerin, so you can compare the two).
posted by ssg at 4:42 PM on July 18, 2008

Glycerin is your best bet as it is a food/pharmaceutical additive, however, remember that it is flammable (as it is an alcohol) and an irritant. Always check out the MSDS sheet for any chemical before you use it (https://fscimage.fishersci.com/msds/10440.htm).
posted by stevechemist at 4:43 PM on July 18, 2008

Seconding Glycerin. It's quite dense and will stay put when put on something else. I've used it tons to mimick water drops and such for product shoots.
posted by arishaun at 4:45 PM on July 18, 2008

Glycerin
posted by kldickson at 5:02 PM on July 18, 2008

"Realistically, I suspect my best bet is a heavy but transparent oil, so it probably won't even be as dense as water, but at least something denser than baby oil. Any idea what that might be?"

Most oils are in the 0.9-0.925 g/cm. Coconut oil is at the dense end of that range so if you want to see if a oil will work it'll be a good test subject. I say test subject because it freezes around 25C. Anything denser than coconut oil is more solid than oil (think tar).

From your list ethylene glycol (IE: standard AntiFreeze) is denser than water but I don't know where you'd get it colourless and it's poisonous. Propylene glycol is an alternative antifreeze that is generally considered safe which is also (barely) denser than water 1.036 g/cm. You can get it coloured a pink or purple at RV supply places (used for winterizing RV water systems) and is used uncoloured for preservation work. Both are hygroscopic so if you also have water in your container they'll mix.

ssg writes "Mineral oil is another possibility."

Baby oil = Mineral oil + scent.
posted by Mitheral at 5:05 PM on July 18, 2008 [1 favorite has favorites]

I'm pretty sure baby oil is just mineral oil. Glycerin's probably a good bet, but at least buying it in the drug store is probably a little expensive (depending on the quantity you need). Light corn syrup might work, too, but it's not "crystal-clear" transparent.
posted by leahwrenn at 5:09 PM on July 18, 2008

Light corn syrup? (But watch out for bubbles and ants.)

If you want something that looks like water but that's actually solid, there's polyurethane -- the kind that comes in what appears to be a paint can. It dries solid and transparent, and can therefore be used to give the illusion that objects are 'floating' in it if you put them in it before it hardens.
posted by sentient at 5:23 PM on July 18, 2008

Yup, glycerin. If you need to go to a chemical supply house to get some, you may have to ask for glycerol (the pure form of the major component of glycerin).

It absorbs moisture from the air, so keep the bottle tightly capped to avoid problems with water messing up your powders. It's slightly flammable so don't use it around open flames, but it's not something we ever worry about in the lab. It's also very viscous and makes a sticky mess, so work carefully or resign yourself to lots of cleanup. On the bright side, it's water-soluble and nontoxic so cleaning it up is merely annoying, not hazardous. (MSDS here for further reference).
posted by Quietgal at 5:33 PM on July 18, 2008

Glycerin is does oxidise fairly easily, though, as the 13-year-old me discovered when adding KMnO₄ to glycerin, and ending up with a frothy purplish explosion.
posted by scruss at 6:33 PM on July 18, 2008

propylene glycol?
posted by ian1977 at 6:56 PM on July 18, 2008

oops...I meant to say....

propylene glycol?
posted by ian1977 at 6:56 PM on July 18, 2008

Keep in mind that if your colored powder is water-soluble, it will also be soluble in glycerol (three hydroxyl groups). Furthermore, if you have access to a lab supplies, you could try dissolving some PEG pellets in toulene (it is not a known carcinogen, that's why I mention it, but other aromatic hydrocarbons should also do) to make the liquid as thick as you please.
posted by halogen at 6:57 PM on July 18, 2008

Oops, that should read toluene.
posted by halogen at 6:59 PM on July 18, 2008

Toluene = flammable + toxic
posted by BrotherCaine at 4:59 AM on July 19, 2008

Another recommendation for glycerol.
posted by springload at 5:17 AM on July 19, 2008

There is a really good two part epoxy product who's name escapes me at the moment, but is available from good craft shops. Being an epoxy it dries solid, and absolutely clear.
posted by mattoxic at 5:27 AM on July 19, 2008

It's envirotex.
posted by Mitheral at 8:23 AM on July 19, 2008

Nobody else seems to have noted this, but if you're swirling something into a liquid, no matter how thick, will eventually disperse thanks to brownian motion. So your best bet may be something that sets into a solid form such as the epoxy mentioned above.
posted by borkencode at 9:10 AM on July 19, 2008

Baby oil = Mineral oil + scent.

Not to be nitpicky, but while that is true, my experience has been that mineral oil (the kind you buy in the pharmacy) is a significantly heavier grade than baby oil.
posted by ssg at 1:48 PM on July 19, 2008

Does it have to be liquid? What about gels? You could use a super clear silicone sealant from a tube, then anything you swirled into it would be locked in a clear gel and would never dissolve or sink. With a lid on top, it would never set, either.
posted by tomble at 8:04 AM on July 20, 2008

Thanks all!
I'll try glycerin first - while I suspect there is a fair chance it might degrade the powder like water does, it still seems like a pretty good bet, and is nicely heavy.
(I'm not sure, since the info I have on the powder is vague, but I'm guessing that oxidizing may be the problem with using water - so if metal left in glycerin would rust or oxidise, then the powder will probably degrade too, but I really don't know, and there is one way to find out for sure - I'll give it a go)

(I'll note the best answers once I've got some real-world results :-)
posted by -harlequin- at 4:11 PM on July 20, 2008

Sorry I'm late to the party.

If you want to make a sol, (relative) density is only one of the factors to consider. The liquid viscosity and the particle size are also very important. The physical factors that make soil in liquid dispersions last are a really small solid particle size and high liquid viscosity. Density, as you've discovered, is hard to play with.

Here's the relationship you need:

rise time ~ (density difference) / (viscosity) * (particle size)^2^*

There is not much you can do with density, because there isn't that wide a range of fluid densities, but there is a huge range (5 orders of magnitude) of viscosities to choose from. That's where you will get you bang for buck. For reference below, water has a density of 1 (in specific gravity units) and a viscosity of near enough 1 cP (mPa.s).

Almost all hydrocarbons and common solvents are not going to do what you want not because of density, but because their viscosities are too low.

Glycerol is a good choice, high density (1.26) and very high viscosity (1200 cP at room temp), but it is hydroscopic---it will absorb water over time if not sealed.

If it's too thick, you might try ethylene glycol (sg 1.1, v 10 cP), but it is mildly poisonous (only if consumed).

Will oils not work at all? USP mineral oil can have a density of up to 0.9 or so and viscosity of around 35 cP. It might be worth a second try. It may be a better alternative than ethylene glycol.

Liquids denser than water are hard to find, and almost none are "safe" (this from a guy who thinks ethylene glycol---antifreeze---is acceptably safe). The most common dense, clear liquids are halocarbons, typically dry-cleaning fluids and the like (sg 1.2-1.4). However, they also have low viscosities (0.6-0.9 cP), lower than water in most cases. (It's a shame you can't use PCBs---they'd be perfect).

Try using the smallest diameter powder you can get away with. As you can see from above, the stability of the sol depends on the square of the particle size. Smaller flakes will make your dispersion last much, much longer than anything else you can adjust.

Finally, can you add anything to stabilize the particles? A drop or two of surfactant might well do the trick. Try experimenting with a drop of dish soap. You don't generally need much (1:200 liq:liq is usually enough) and the results can be dramatic.
posted by bonehead at 10:11 AM on July 21, 2008 [1 favorite has favorites]