Editing Iridescence

{{Short description|Optical property}}
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{{use British English|date=February 2014}}
[[File:Soap Bubble - foliage background - iridescent colours - Traquair 040801.jpg|thumb|upright=1.25|Iridescence in [[soap bubble]]s]]

'''Iridescence''' (also known as '''goniochromism''') is the phenomenon of certain surfaces that appear [[Gradient|gradually]] to change [[colour]] as the angle of view or the angle of illumination changes. Iridescence is caused by [[wave interference]] of light in [[microstructure]]s or [[thin-film interference|thin films]]. Examples of iridescence include [[soap bubble]]s, [[feather]]s, [[butterfly]] wings and seashell [[nacre]], and minerals such as [[opal]]. '''[[Iridescence#Pearlescence|Pearlescence]]''' is a related effect where some or most of the reflected light is white. The term pearlescent is used to describe certain paint finishes, usually in the automotive industry, which actually produce iridescent effects.

== Etymology ==
The word ''iridescence'' is derived in part from the [[Greek language|Greek]] word ἶρις ''îris'' ([[Genitive|gen.]] ἴριδος ''íridos''), meaning ''[[rainbow]]'', and is combined with the Latin suffix ''-escent'', meaning "having a tendency toward".<ref>{{cite web|url=http://www.etymonline.com/index.php?term=-escent|title=Online Etymology Dictionary|work=etymonline.com|url-status=live|archive-url=https://web.archive.org/web/20140407103248/http://www.etymonline.com/index.php?term=-escent|archive-date=2014-04-07}}</ref> Iris in turn derives from the goddess [[Iris (mythology)|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".

== Mechanisms ==
[[File:Dieselrainbow.jpg|thumb|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. This phenomenon is known as [[thin-film interference]]. ]]
{{further|Structural coloration|thin-film interference|diffraction}}

Iridescence is an [[optical phenomenon]] of surfaces in which [[hue]] changes with the angle of observation and the angle of illumination.<ref name="srinivasarao">{{cite journal |last1=Srinivasarao |first1=Mohan |title=Nano-Optics in the Biological World: Beetles, Butterflies, Birds, and Moths |journal=Chemical Reviews |date=July 1999 |volume=99 |issue=7 |pages=1935–1962 |doi=10.1021/cr970080y |pmid=11849015 }}</ref><ref>{{cite journal |last1=Kinoshita |first1=S |last2=Yoshioka |first2=S |last3=Miyazaki |first3=J |s2cid=53068819 |title=Physics of structural colors |journal=Reports on Progress in Physics |date=1 July 2008 |volume=71 |issue=7 |pages=076401 |doi=10.1088/0034-4885/71/7/076401 |bibcode=2008RPPh...71g6401K }}</ref> It is often caused by multiple reflections from two or more semi-transparent surfaces in which [[phase (waves)|phase shift]] and [[Interference (wave propagation)|interference]] of the reflections [[amplitude modulation|modulates]] the incidental [[light]], by amplifying or attenuating some frequencies more than others.<ref name="srinivasarao" /><ref name="meadows">{{cite journal |last1=Meadows |first1=Melissa G |last2=Butler |first2=Michael W |last3=Morehouse |first3=Nathan I |last4=Taylor |first4=Lisa A |last5=Toomey |first5=Matthew B |last6=McGraw |first6=Kevin J |last7=Rutowski |first7=Ronald L |title=Iridescence: views from many angles |journal=Journal of the Royal Society Interface |date=23 February 2009 |volume=6 |issue=suppl_2 |pages=S107-13 |doi=10.1098/rsif.2009.0013.focus |pmid=19336343 |pmc=2706472 }}</ref> The thickness of the layers of the material determines the interference pattern. Iridescence can for example be due to [[thin-film interference]], the functional analogue of selective wavelength attenuation as seen with the [[Fabry–Pérot interferometer]], and can be seen in oil films on water and soap bubbles. Iridescence is also found in plants, animals and many other items. The range of colours of natural iridescent objects can be narrow, for example shifting between two or three colours as the viewing angle changes,<ref name="yoshioka">{{cite journal |last1=Yoshioka |first1=S. |last2=Matsuhana |first2=B. |last3=Tanaka |first3=S. |last4=Inouye |first4=Y. |last5=Oshima |first5=N. |last6=Kinoshita |first6=S. |title=Mechanism of variable structural colour in the neon tetra: quantitative evaluation of the Venetian blind model |journal=Journal of the Royal Society Interface |date=16 June 2010 |volume=8 |issue=54 |pages=56–66 |doi=10.1098/rsif.2010.0253 |pmid=20554565 |pmc=3024824 }}</ref><ref>{{cite journal |last1=Rutowski |first1=R.L |last2=Macedonia |first2=J.M |last3=Morehouse |first3=N |last4=Taylor-Taft |first4=L |title=Pterin pigments amplify iridescent ultraviolet signal in males of the orange sulphur butterfly |journal=Proceedings of the Royal Society B: Biological Sciences |date=2 September 2005 |volume=272 |issue=1578 |pages=2329–2335 |doi=10.1098/rspb.2005.3216 |pmid=16191648 |pmc=1560183 }}</ref>

[[File:Iridescent biofilm on a fishtank.JPG|thumb|left|An iridescent [[biofilm]] on the surface of a fish tank diffracts the reflected light, displaying the entire spectrum of colours. Red is seen from longer angles of incidence than blue.]]
Iridescence can also be created by [[diffraction]]. This is found in items like CDs, DVDs, some types of [[Prism (optics)|prism]]s, or [[cloud iridescence]].<ref>{{cite book |last1=Ackerman |first1=Steven A. |last2=Knox |first2=John A. |title=Meteorology: Understanding the Atmosphere |date=2013 |publisher=Jones & Bartlett Learning |isbn=978-1-284-03080-8 |pages=173–175 }}</ref> In the case of diffraction, the entire rainbow of colours will typically be observed as the viewing angle changes. In biology, this type of iridescence results from the formation of [[diffraction grating]]s on the surface, such as the long rows of cells in [[striated muscle]], or the specialized abdominal scales of [[peacock spider]] ''Maratus robinsoni'' and ''M. chrysomelas''.<ref>{{cite journal |last1=Hsiung |first1=Bor-Kai |last2=Siddique |first2=Radwanul Hasan |last3=Stavenga |first3=Doekele G. |last4=Otto |first4=Jürgen C. |last5=Allen |first5=Michael C. |last6=Liu |first6=Ying |last7=Lu |first7=Yong-Feng |last8=Deheyn |first8=Dimitri D. |last9=Shawkey |first9=Matthew D. |last10=Blackledge |first10=Todd A. |title=Rainbow peacock spiders inspire miniature super-iridescent optics |journal=Nature Communications |date=22 December 2017 |volume=8 |issue=1 |page=2278 |doi=10.1038/s41467-017-02451-x |pmid=29273708 |pmc=5741626 |bibcode=2017NatCo...8.2278H }}</ref> Some types of flower petals can also generate a diffraction grating, but the iridescence is not visible to humans and flower-visiting insects as the diffraction signal is masked by the colouration due to [[plant pigments]].<ref>{{cite book |last1=Lee |first1=David |title=Nature's Palette: The Science of Plant Color |date=2007 |publisher=University of Chicago Press |isbn=978-0-226-47052-8 }}{{pn|date=June 2020}}</ref><ref>{{cite journal |last1=van der Kooi |first1=Casper J. |last2=Wilts |first2=Bodo D. |last3=Leertouwer |first3=Hein L. |last4=Staal |first4=Marten |last5=Elzenga |first5=J. Theo M. |last6=Stavenga |first6=Doekele G. |title=Iridescent flowers? Contribution of surface structures to optical signaling |journal=New Phytologist |date=July 2014 |volume=203 |issue=2 |pages=667–673 |doi=10.1111/nph.12808 |pmid=24713039 |url=https://pure.rug.nl/ws/files/16807700/vanderKooi_Etal2014_NewPhytologist.pdf |doi-access=free |bibcode=2014NewPh.203..667V }}</ref><ref>{{cite journal |last1=van der Kooi |first1=Casper J. |last2=Dyer |first2=Adrian G. |last3=Stavenga |first3=Doekele G. |title=Is floral iridescence a biologically relevant cue in plant-pollinator signaling? |journal=New Phytologist |date=January 2015 |volume=205 |issue=1 |pages=18–20 |doi=10.1111/nph.13066 |pmid=25243861 |doi-access=free |bibcode=2015NewPh.205...18V }}</ref>

In biological (and [[biomimetic]]) uses, colours produced other than with [[pigment]]s or [[dye]]s are called [[structural colouration]]<!-- -or- is UK spelling here -->. Microstructures, often multi-layered, are used to produce bright but sometimes non-iridescent colours: quite elaborate arrangements are needed to avoid reflecting different colours in different directions.<ref>{{cite journal |last1=Hsiung |first1=Bor-Kai |last2=Siddique |first2=Radwanul Hasan |last3=Jiang |first3=Lijia |last4=Liu |first4=Ying |last5=Lu |first5=Yongfeng |last6=Shawkey |first6=Matthew D. |last7=Blackledge |first7=Todd A. |title=Tarantula-Inspired Noniridescent Photonics with Long-Range Order |journal=Advanced Optical Materials |date=January 2017 |volume=5 |issue=2 |pages=1600599 |doi=10.1002/adom.201600599 |doi-access= |s2cid=100181186 |url=https://biblio.ugent.be/publication/8550548/file/8651402 |url-access=subscription }}</ref> Structural colouration 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.<ref name=HookeOnPeacockIridescence>Hooke, Robert. Micrographia. Chapter 36 ('Observ. XXXVI. ''Of Peacoks, Ducks, and Other Feathers of Changeable Colours''.')</ref><ref name=Ball>{{cite journal |last1=Ball |first1=Philip |title=Nature's Color Tricks |journal=Scientific American |date=17 April 2012 |volume=306 |issue=5 |pages=74–79 |doi=10.1038/scientificamerican0512-74 |doi-broken-date=1 November 2024 |pmid=22550931 |bibcode=2012SciAm.306e..74B }}</ref> It was later found that iridescence in the peacock is due to a complex [[photonic crystal]].<ref name="peacock">{{cite journal |last1=Zi |first1=Jian |last2=Yu |first2=Xindi |last3=Li |first3=Yizhou |last4=Hu |first4=Xinhua |last5=Xu |first5=Chun |last6=Wang |first6=Xingjun |last7=Liu |first7=Xiaohan |last8=Fu |first8=Rongtang |title=Coloration strategies in peacock feathers |journal=Proceedings of the National Academy of Sciences of the United States of America |date=28 October 2003 |volume=100 |issue=22 |pages=12576–12578 |doi=10.1073/pnas.2133313100 |pmid=14557541 |pmc=240659 |bibcode=2003PNAS..10012576Z |doi-access=free }}</ref>

== Pearlescence ==
[[File:Black pearl and his shell.jpg|thumb|The pearlescent shell of a [[black-lip pearl oyster]]]]
Pearlescence is an effect related to iridescence and has a similar cause. Structures within a surface cause light to be reflected back, but in the case of pearlescence some or most of the light is white, giving the object a [[pearl]]-like luster.<ref name=pearleasence>{{cite book|author=Ruth Johnston-Feller|title=Color Science in the Examination of Museum Objects: Nondestructive Procedures|url=https://books.google.com/books?id=HtoxCwAAQBAJ&pg=PA169|year=2001|publisher=Getty Publications|isbn=978-0-89236-586-9|pages=169–}}</ref> Artificial pigments and paints showing an iridescent effect are often described as pearlescent, for example when used for [[car paint]]s.<ref name=paint>{{cite book|title=Paint and Coating Testing Manual|url=https://books.google.com/books?id=ri6FkY2xvgcC&pg=PA229|publisher=ASTM International|pages=229–|id=GGKEY:7W7C2G88G2J}}</ref><ref>{{Cite web |date=2023-04-20 |title=Powder Pearls Manufacturing: A Comprehensive Guide |url=https://thecandeshop.com/powder-pearls/ |access-date=2025-02-28 |website=thecandeshop.com |language=en-US}}</ref>

== Examples ==

=== Life ===

==== Invertebrates ====
''[[Eledone moschata]]'' has a bluish iridescence running along its body and [[Tentacle|tentacles]].<ref>{{Cite web |last=Mazza |first=Giuseppe |date=2008-08-07 |title=Eledone moschata |url=https://www.monaconatureencyclopedia.com/eledone-moschata/?lang=en |access-date=2023-02-07 |website=Monaco Nature Encyclopedia |language=en-US}}</ref><gallery class="center">
File:Iridescent Insect Display.png|Cornell drawer displaying iridescent insects
File:Female Golden Stag Beetle.jpg|The iridescent exoskeleton of a golden [[stag beetle]]
File:Morpho didius Male Dos MHNT.jpg|[[Structural coloration|Structurally coloured]] wings of ''[[Morpho didius]]''
File:Eunice aphroditois.jpg|The iridescent skin of a [[Bobbit worm]], ''Eunice aphroditois''
File:Haliotis iris LC0283.jpg|The inside surface of ''[[Haliotis iris]]'', the paua shell
</gallery>

==== Vertebrates ====
The [[feather]]s of birds such as [[kingfisher]]s,<ref>{{cite journal |last1=Stavenga |first1=D. G. |last2=Tinbergen |first2=J. |last3=Leertouwer |first3=H. L. |last4=Wilts |first4=B. D. |title=Kingfisher feathers – colouration by pigments, spongy nanostructures and thin films |journal=Journal of Experimental Biology |date=9 November 2011 |volume=214 |issue=23 |pages=3960–3967 |doi=10.1242/jeb.062620 |pmid=22071186 |doi-access=free |bibcode=2011JExpB.214.3960S }}</ref> [[birds-of-paradise]],<ref>{{cite journal |last1=Stavenga |first1=Doekele G. |last2=Leertouwer |first2=Hein L. |last3=Marshall |first3=N. Justin |last4=Osorio |first4=Daniel |title=Dramatic colour changes in a bird of paradise caused by uniquely structured breast feather barbules |journal=Proceedings of the Royal Society B: Biological Sciences |date=15 December 2010 |volume=278 |issue=1715 |pages=2098–2104 |doi=10.1098/rspb.2010.2293 |pmid=21159676 |pmc=3107630 }}</ref> [[hummingbird]]s, [[parrot]]s, [[starling]]s,<ref>{{cite journal |last1=Cuthill |first1=I. C. |last2=Bennett |first2=A. T. D. |last3=Partridge |first3=J. C. |last4=Maier |first4=E. J. |title=Plumage Reflectance and the Objective Assessment of Avian Sexual Dichromatism |journal=The American Naturalist |date=February 1999 |volume=153 |issue=2 |pages=183–200 |doi=10.1086/303160 |pmid=29578758 |jstor=303160 |bibcode=1999ANat..153..183C |s2cid=4386607 }}</ref> [[grackle]]s, [[duck]]s, and [[peacock]]s<ref name="peacock" /> are iridescent. The lateral line on the [[neon tetra]] is also iridescent.<ref name="yoshioka" /> A single iridescent species of gecko, ''[[Cnemaspis kolhapurensis]]'', was identified in India in 2009.<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/world/south_asia/8166904.stm |title=New lizard species found in India|date=24 July 2009 |work=[[BBC Online]] |access-date=20 February 2014}}</ref> The [[tapetum lucidum]], present in the [[eye]]s of many vertebrates, is also iridescent.<ref>{{cite book |last=Engelking|first=Larry |title=Review of Veterinary Physiology|year=2002 |publisher=Teton NewMedia |isbn=978-1-893441-69-9 |page=90}}</ref> Iridescence is known to be present among prehistoric non-avian and avian dinosaurs such as [[Dromaeosauridae|dromaeosaurids]], [[enantiornithes]], and [[Lithornithidae|lithornithids]].<ref>{{cite journal |last1=Eliason |first1=Chad M. |last2=Clarke |first2=Julia A. |title=Cassowary gloss and a novel form of structural color in birds |journal=Science Advances |date=13 May 2020 |volume=6 |issue=20 |pages=eaba0187 |doi=10.1126/sciadv.aba0187 |pmid=32426504 |pmc=7220335|bibcode=2020SciA....6..187E }}</ref>  Muscle tissues can display irisdescence.  <ref>{{cite journal |title= Iridescence in Meat Caused by Surface Gratings |journal=Foods |date=2013-11-11 |doi=10.3390/foods2040499 |doi-access=free |last1=Martinez-Hurtado |first1=Juan |last2=Akram |first2=Muhammad |last3=Yetisen |first3=Ali |volume=2 |issue=4 |pages=499–506 |pmid=28239133 |pmc=5302279 }}</ref>

<gallery class="center">
File:Peacock 2.jpg|Both the body and the train of the peacock are iridescent
File:NeonTetra.JPG|A [[neon tetra]]
File:Rainbow boa peruvian.jpg|The [[rainbow boa]]
File:Nicobar Pigeon 820.jpg|[[Nicobar pigeon]]
</gallery>

==== Plants ====
Many groups of plants have developed iridescence as an adaptation to use more light in dark environments such as the lower levels of tropical forests. The leaves of Southeast Asia's ''[[Begonia pavonina]]'', or peacock begonia, appear iridescent azure to human observers due to each leaf's thinly layered photosynthetic structures called iridoplasts that absorb and bend light much like a film of oil over water. Iridescences based on multiple layers of cells are also found in the [[lycophyte]] ''[[Selaginella]]'' and several species of [[ferns]].<ref>{{Cite journal |last1=Glover |first1=Beverley J. |last2=Whitney |first2=Heather M. |date=April 2010 |title=Structural colour and iridescence in plants: the poorly studied relations of pigment colour |journal=Annals of Botany |volume=105 |issue=4 |pages=505–511 |doi=10.1093/aob/mcq007 |pmid=20142263 |pmc=2850791 }}</ref><ref>{{Cite journal |last1=Graham |first1=Rita M. |last2=Lee |first2=David W. |last3=Norstog |first3=Knut |date=1993 |title=Physical and Ultrastructural Basis of Blue Leaf Iridescence in Two Neotropical Ferns |jstor=2445040 |journal=American Journal of Botany |volume=80 |issue=2 |pages=198–203 |doi=10.2307/2445040 }}</ref>

<gallery class="center">
File:Iridescent begonia.jpg|Iridescent ''[[Begonia]]'' leaf
File:Peacock Fern (Selaginella wildenowii) (8681119528).jpg|''[[Selaginella wildenowii]]'' leaves
File:Pollia.jpg|''[[Pollia condensata]]'' fruits
File:Ophrys speculum-IMG 0321.jpg|''[[Ophrys speculum]]'' flowers
</gallery>

=== Non-biological ===

==== Minerals ====
<gallery class="center">
File:Wismut Kristall und 1cm3 Wuerfel.jpg|A [[bismuth]] crystal with a thin iridescent layer of [[bismuth oxide]], with a whitish-silver bismuth cube for comparison
File:Goethite-171990.jpg|[[Goethite]], an [[iron(III) oxide-hydroxide]], from [[Polk County, Arkansas]]
File:Ladrador iridescence.jpg|Polished [[labradorite]]
</gallery>

==== Meteorological ====
<gallery class="center">
File:Polar Stratospheric Clouds.jpg|[[Polar stratospheric cloud|Polar stratospheric clouds]] displaying a [[Nacreous]] iridescence
File:Irid clouds1.jpg|[[Cloud iridescence]]
</gallery>

==== Human-made ====
<gallery class="center" mode="packed">
File:Pearlescent Toyota Supra - 002.jpg|[[Pearlescent paint]] job on a [[Toyota Supra]] car
File:8 cd-da disc-to-1 mini mp3-cd.jpg|Playing surface of [[Compact disc|compact discs]]
File:1899 reverse.jpg|Iridescent [[toning (coin)|toning]] on the reverse of a [[Morgan dollar]]
File:Glitter nail polish (purple).jpg|Iridescent [[glitter]] [[nail polish]]
File:Samsung Galaxy A50 back 2.jpg|[[Smartphone]] with iridescent back panel
File:Engine oil rainbow p1120058.jpg|An [[engine oil]] spill
File:Tempering standards used in blacksmithing.JPG|[[Tempering (metallurgy)#Tempering colors|Tempering colours]] are formed by heating steel, forming a thin oxide-film on the surface. The colour indicates the temperature it was heated to, making it one of the earliest practical uses of iridescence.
</gallery>

[[Nanocellulose]] is sometimes iridescent,<ref name="PicardSimon2012">{{cite journal |last1=Picard |first1=G. |last2=Simon |first2=D. |last3=Kadiri |first3=Y. |last4=LeBreux |first4=J. D. |last5=Ghozayel |first5=F. |title=Cellulose Nanocrystal Iridescence: A New Model |journal=Langmuir |date=3 October 2012 |volume=28 |issue=41 |pages=14799–14807 |doi=10.1021/la302982s |pmid=22988816 }}</ref> as are thin films of [[petrol]] and some other [[hydrocarbon]]s and [[Alcohol (chemistry)|alcohol]]s when floating on water.<ref>{{cite book|last=Zitzewitz|first=Paul W|title=The Handy Physics Answer Book|url=https://books.google.com/books?id=qGTkgFZBJZQC&pg=PA215|year=2011|publisher=Visible Ink Press|isbn=978-1-57859-357-6|page=215}}</ref>

== See also ==
{{div col|colwidth=22em}}
* [[Anisotropy]]
* [[Bioluminescence]], irrespective of angle
* [[Dichroic filter]]
* [[Dichroism]]
* [[Iridocyte]]
* [[Labradorescence]] (Adularescence)
* [[Metallic colour]]
* [[Opalescence]]
* [[Structural colour]]
* [[Thin-film optics]]
* [[Nacre]]
* [[Opal]]
{{div col end}}

== References ==
{{Reflist|30em}}

== External links ==
{{Commons}}
* [https://web.archive.org/web/20060527203958/http://astro.ensc-rennes.fr/funny_physics/morpho_anim_3.gif A 2.2 MB GIF animation] of a morpho butterfly showing iridescence
* [http://www.physics.org/featuredetail.asp?NewsId=22 "Article on butterfly iridescence"] {{Webarchive|url=https://web.archive.org/web/20151107012605/http://www.physics.org/featuredetail.asp?NewsId=22 |date=2015-11-07 }}

[[Category:Optics]]
[[Category:Optical phenomena]]
[[Category:Color]]