A butterfly’s iridescent wings can change color when soaked in a liquid, but the original color returns when the liquid evaporates

A butterfly’s iridescent wings can change color when soaked in a liquid, but the original color returns when the liquid evaporates

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About the Author: livescience


  1. **Explanation**

    Unlike most common materials, the vivid blue color of the Morpho butterfly does not come from dyes or pigments. Instead, it is an example of [structural coloration](https://en.wikipedia.org/wiki/Structural_coloration). Put very simply, this idea means that the way in which a material is structured determines what colors are transmitted and which are reflected. Under an electron microscope, you can see that the wing of the butterfly is made up of an orderly array of flakes [as you can see here](http://i.imgur.com/fpyRcGn.png). The flakes are arranged in a 3D grating type structure, [that looks like this](http://i.imgur.com/sa0qzcZ.png).^2 The spacing in these structures is on the order of hundreds of nanometers, similar to the wavelength of visible light.

    This structure allows the wing to work as a [photonic crystal](https://en.wikipedia.org/wiki/Photonic_crystal), [as shown in this cartoon](http://i.imgur.com/heeGs6G.png). That means that the structure will preferentially reflect different wavelengths of light depending on the angle of the source. This effect is similar to the interference that produces those bright colors in soap bubbles. In the case of the Morpho butterflies, the structure is shaped in such a way that blue color is preferentially reflected [as you can see from this spectrum](http://i.imgur.com/5mv63wY.png). As a result, the wing normally looks bright blue as you see at the beginning of the GIF. However, as soon as you add a solvent (in this case isopropanol or rubbing alcohol) to fill in these pores, the blue color suddenly goes away. The reason for that is that the solvent has a different index of refraction than air and so you no longer get the same rules for constructive interference. However as soon as the solvent dries off, the bright blue color comes right back.


    1. The GIF came from [this video](https://www.youtube.com/watch?v=LE2v3sUzTH4)

    2. Ding, Y. Structural colors from Morpho peleides butterfly wing scales. *J. Appl. Phys.* 2009: 106, 074702

    3. Van Hooijdonk, E., et al. Detailed experimental analysis of the structural fluorescence in the butterfly Morpho sulkowskyi (Nymphalidae) *J. Nanophoton.* 2011: 5(1), 053525

  2. I don’t know why, but I love it when color is caused by nanoscopic physical properties rather than chemical properties. I’m doing research on nanoparticle synthesis, and they’re small enough to be affected by quantum confinement.

    We use cadmium selenide, which is usually red in its bulk state, but the particles we make are so small (3 to 6nm) that they can’t absorb red wavelengths of light. So as these particles are forming I get to watch the solution change from clear to green (skips blue for some reason), to yellow, to orange, and sometimes red if we make them large enough.

    Every time I make them it just blows my mind that these particles are so small it causes their color to change.

  3. Not a chemical reaction so much a a physical chemistry trait. The microstructure corresponds to certain wavelengths, this generating a color. You fill some of the “holes” with ethanol or isopropanol mixture and only certain light is visible even more so.

  4. Really? Last time I checked anything you soak in liquid changes color. IE rocks when they get wet are a different color than when dry. Your clothes are a different color when wet then when dry, your hair is a different color when wet than when dry.

  5. So, what I got from this, someone is paid to sit around and pour water on butterflies?

    I need to fix my resume.

  6. There’s some really pissed off butterfly walking about wondering what the hell happened to his wings last night. On the plus side, he doesn’t drink to excess anymore.

  7. Why is no one hypothesizing that the reason the butterfly’s wings turn green is to remain camouflaged in a rain storm?

  8. This is a reason to preserve our wildlife nature continues to make things humans just can’t yet, but with the right tools and knowledge people could remake them and apply them in unlimited ways even the study of how butterfly wings change color when wet could be a potential piece of technological advances.

  9. Huh, so if it rains, then the butterfly’s wings will become darker and more green, almost like camouflage for when it’s wet and can’t fly/escape predators. However, as soon as it dries off, it will return to it’s usual color and be able to fly from danger. Cool.

  10. This structure is also what gives blue-eyed people their blue eyes, while brown-eyed people get their color from pigment.

  11. They picked a poor chemical to use for the demo. When I do this I use Ethel acetate or acetone. The wing turns a much darker color like brick red and you can blow on the wing and the chemical evaporates almost instantly allowing for the blue to snap back like magic.

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