I want to create a decoration - a mason jar "aquarium". I want to take a large mason jar, put some nice mineral specimens in it, fill the jar with liquid and seal it with lid.

I believe I can't use pure water because there is a chance that it will go bad after some time.

So I want to know if there is some liquid that is not too aggressive (in terms of mineral decay) or dangerous that has indefinite shelf life. I want it to last for years.

I know that vodka basically never goes bad, but it's pretty expensive and the alcohol would probably be too harsh for the minerals in the jar.

Additional information: I am considering water with salt.

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    $\begingroup$ You'll want as inert a solution as possible, and vodka contains water. Consider mineral oil: it's cheap, transparent to visible light, is generally non-toxic in the setting you suggest (sealed container), and won't react with many minerals . What minerals are you considering putting in our display? $\endgroup$ – Todd Minehardt Sep 6 '16 at 2:06
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    $\begingroup$ Vodka would be probably less harsh for the minerals than water with salt. Depends on the minerals, though. Most minerals would withstand both just fine. After all, salt itself is a mineral. Thinking of salt crystals in a saturated brine... well, that may looks nice, and may last forever, unless the lid is made of metal and the brine eats through it. $\endgroup$ – Ivan Neretin Sep 6 '16 at 7:56
  • $\begingroup$ DO NOT USE WATER WITH SALT. This is just about the worst thing you can do. Some minerals will dissolve and corrode with time in salt solutions. Vodka is not too harsh, but the ethanol is volatile and it has water in it. Mineral oil is better. Air is the best: I wouldn't use any liquids at all. $\endgroup$ – Gimelist Sep 8 '16 at 12:03

There are three things to take into consideration here: volatility of the liquid you will be using (yes, the jar will be tightly closed, but some candidates might still evaporate slowly and/or have toxic or foul-smelling vapors), stability, and refraction index. Mineral oil is a great candidate, as Todd Minehardt commented. It's really stable, releases no vapors whatsoever, but its refractive index is a little higher than that of water, which might make your aquarium look funny. There are substances with similar properties that might be useful and also readily available, but with a refractive index closer to water's. Amyl alcohol (fusel oil) or ethylene glycol (car antifreeze) are good candidates and shouldn't be too hard to find. Glycerol and propylene glycol are also pretty good options, but their refractive indexes are closer to mineral oil than the other two.


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