I was thinking of an alien humanoid charcter for my super powered beings story that would be completely black and faceless with similarities to venom and its strings of symbiotic goo but this character would not be a symbiotic life form.

I thought that the rainbow colours seen on oil spills on puddles especially on bumpy black tarmac look beautiful and almost sinister at the same time (maybe its the rainbow colours on black or the flammable danger factor) and that this effect would look good on the aliens skin.

I was told that it doesn't have to be water with a thin film of oil that can create these colours as the light reflects from both above and below the oil layer but any polar solvent can be used instead of water (if this is incorrect can anyone name a suitable substance instead please)

I thought that the alien could sweat or secrete both the polar solvent and oil from its black textured skin and be covered or at times only parts of its body will have the rainbow light effect.

So my question is which polar solvent or any other substance would make an interesting base for the oil to create its rainbow pattern and could also itself serve as a weapon or have other useful properties that would be much better than water?

At first I thought Acetic acid or Formic acid could be interesting as they could be used as mild weapons themselves, I believe theres an ant that stings with formic acid, although very mild in terms of super powers in high concentrations this could be an effective weapon if spat out.

As this is an early stage of character design i still need to design its home planet and some of its abilities but with an idea of what solvent it secretes will help with those aspects of this character.

EDIT: the question was more about the properties of polar solvents and which have the most interesting chemical qualities that could be tweaked into a superpower either in combination with the oil burning like ethanal or a differnet effect entirley of its own. i added the word substances to the title as i was unsure if other liquids could work the same as water.


Many insects already have hulks which are optical crystals, i.e. iridescent (what you are looking for here).


Birds also have iridescent feathers, like the common pigeon. Their feathers sometimes look green: they aren't, it's an optical effect.

fancy pigeon

So, basically, it may be some substance (oil?) which just makes optical properties of their skin apparent.

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    $\begingroup$ that stag beetle looks pretty cool but it was the fluidity of the colour changes on a bland background colour I was more after. $\endgroup$
    – user59653
    Oct 1 '19 at 21:14
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    $\begingroup$ @rag haran: You would still have a pretty good chance of achieving an effect like that with structural colors: en.wikipedia.org/wiki/Structural_coloration Indeed, that irridescent oil film is a structural color, like the rainbow reflections from a CD. $\endgroup$
    – jamesqf
    Oct 2 '19 at 3:15
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    $\begingroup$ @ragharan you can already see that color is fluid - different portions of body look different color, but the hide is actually the same material. Color depends on POV, not on location relative to hide. $\endgroup$
    – alamar
    Oct 2 '19 at 8:47
  • $\begingroup$ I see what you both mean but with a film on liquid, if you can control the flow of liquid you can greatly and constantly keep changing the patern and not just dependent on POV from the light $\endgroup$
    – user59653
    Oct 2 '19 at 9:51
  • $\begingroup$ I don't really think that you can cause film of liquid to flow. Otherwise, should work like a charm. $\endgroup$
    – alamar
    Oct 2 '19 at 12:49

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