Iridescence

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Iridescence in soap bubbles
Iridescence in soap bubble film
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Iridescence (also known as goniochromism) is generally known as the property of certain surfaces that appear to change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, butterfly wings and sea shells.

Description

Further information: Structural coloration

Iridescence is an optical phenomenon of surfaces in which hue changes in proportion to the angles of observation and illumination. It is often caused by multiple reflections from two or more semi-transparent surfaces in which phase shift and interference of the reflections modulates the incidental light (by amplifying or attenuating some frequencies more than others).[1] This process, termed thin-film interference, is the functional analog of selective wavelength attenuation as seen with the Fabry–Pérot interferometer.

In biological (and biomimetic) uses, colours are traditionally produced with pigments, so colours produced other than by pigment are called structural coloration. Microstructures, often multilayered, are often used to produce iridescence, as quite elaborate arrangements are needed to avoid reflecting different colours in different directions. Structural coloration has been understood in general terms since Robert Hooke's 1665 book Micrographia, where Hooke correctly noted that since the iridescence of a peacock's feather was lost when it was plunged into water, but reappeared when it was returned to the air, pigments could not be responsible.[2][3]

Etymology

The word iridescence is derived in part from the Greek word ἶρις îris (gen. ἴριδος íridos), meaning rainbow, which in turn derives from the goddess Iris of Greek mythology, who is the personification of the rainbow and acted as a messenger of the gods. Goniochromism is derived from the Greek words gonia, meaning "angle", and chroma, meaning "color".

Examples

Arthropods and mollusks

  • A female golden stag beetle has an iridescent exoskeleton

  • A Morpho didius butterfly has iridescent wings

  • The iridescent inside surface of a Paua shell

  • The wings of Tachinid fly demonstrate iridescent colors that are due to the surface structures

Chordates

The feathers of some birds, such as kingfishers, hummingbirds, parrots, crows, ravens, starlings, grackles, ducks, and peacocks are often iridescent. A single iridescent species of gecko, Cnemaspis kolhapurensis, was identified in India in 2009.[citation needed] The tapetum lucidum, present in the eyes of many vertebrates, may also be iridescent.

  • A peacock has iridescent tail feathers

  • A catfish with iridescent scales

  • Rainbow boas get their name from the iridescence of their scales.

Minerals and compounds

Others

Nanocellulose is sometimes iridescent as well. Gasoline and some other hydrocarbons and alcohols are often iridescent when floating on water in a thin film.

See also

References

  1. ↑ "Iridescence in Lepidoptera". Photonics in Nature (originally in Physics Review). University of Exeter. September 1998. Retrieved April 27, 2012. 
  2. ↑ Hooke, Robert. Micrographia. Chapter 36 ('Observ. XXXVI. Of Peacoks, Ducks, and Other Feathers of Changeable Colours.')
  3. ↑ Ball, Philip (May 2012). "Scientific American". Nature's Color Tricks 306 (5): 74–79. doi:10.1038/scientificamerican0512-74. PMID 22550931. Retrieved April 23, 2012. 

External links

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