Iridescence

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Iridescence in soap bubbles

Iridescence (also known as goniochromism) is the property of certain surfaces that appear to change colour as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, butterfly wings and sea shells, as well as certain minerals. It is often created by structural coloration (microstructures which interfere with light).

Mechanisms[edit]

Fuel on top of water creates a thin film, which interferes with the light, producing different colours. The different bands represent different thicknesses in the film.
An iridescent biofilm on the surface of a fishtank diffracts the reflected light, displaying the entire spectrum of colours. Red is seen from longer angles of incidence than blue.

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 analogue of selective wavelength attenuation as seen with the Fabry–Pérot interferometer. This is usually seen in plants and animals, soap bubbles, oil films on water, and many other items. In this case, the range of colours will often be rather narrow, usually shifting between two or three colours as the viewing angle changes, while changes in the thickness of the film will produce bands of colours that do not match the rainbow-spectrum, including browns, magentas, purples and blues.[2]

Iridescence can also be created by diffraction. This is found in items like CDs, DVDs, or cloud iridescence.[3] In the case of diffraction, the entire rainbow of colours will typically be observed as the viewing angle changes. Iridescence from diffraction is rare in plants and animals, but does occur in some marine invertebrates, like seed shrimp or Burgess shale fossils.[4] In biology, this type of iridescence results from the formation of diffraction gratings on the surface, such as the long rows of cells in striated muscle or in some types of flower petals.[5]

In biological (and biomimetic) uses, colours produced other than with pigments or dyes are called structural coloration. Microstructures, often multilayered, are used to produce bright but sometimes non-iridescent colours: 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.[6][7]

Etymology[edit]

The word iridescence is derived in part from the Greek word ἶρις îris (gen. ἴριδος íridos), meaning rainbow, and is combined with the Latin suffix -escent, meaning "having a tendency toward."[8] Iris 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 "colour".

Examples[edit]

Animals[edit]

Arthropods and molluscs[edit]

Chordates[edit]

The feathers of birds such as kingfishers, hummingbirds, parrots, crows, ravens, starlings, grackles, ducks, and peacocks are iridescent. A single iridescent species of gecko, Cnemaspis kolhapurensis, was identified in India in 2009.[9] The tapetum lucidum, present in the eyes of many vertebrates, is also iridescent.[10]

Meat[edit]

Minerals and compounds[edit]

Man made objects[edit]

Nanocellulose is sometimes iridescent, as are thin films of gasoline and some other hydrocarbons and alcohols when floating on water.

See also[edit]

References[edit]

  1. ^ "Iridescence in Lepidoptera". Photonics in Nature (originally in Physics Review). University of Exeter. September 1998. Retrieved April 27, 2012. 
  2. ^ Lee, David W. (2007). Nature's palette: the science of plant color. University of Chicago Press. pp. 255–256. 
  3. ^ Meteorology By Professor of Atmospheric and Oceanic Sciences University of Wisconsin-Madison Director Cooperative Institute for Meteorological Satellite Studies (Cimss) Steven A Ackerman, Steven A. Ackerman, John A. Knox -- Jones and Bartlett Learning 2013 Page 173--175
  4. ^ Nature's palette: the science of plant color By David Webster Lee - University of Chicago Press 2007 Page 41
  5. ^ Kolle, Mathias (2011). Photonic Structures Inspired by Nature. Springer. p. 39. 
  6. ^ Hooke, Robert. Micrographia. Chapter 36 ('Observ. XXXVI. Of Peacoks, Ducks, and Other Feathers of Changeable Colours.')
  7. ^ 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. 
  8. ^ http://www.etymonline.com/index.php?term=-escent
  9. ^ "New lizard species found in India". BBC Online. 24 July 2009. Retrieved 20 February 2014. 
  10. ^ Engelking, Larry (2002). Review of Veterinary Physiology. Teton NewMedia. p. 90. ISBN 1893441695. 

External links[edit]