Iridescence

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

Pearlescence is a related effect where some or all of the reflected light is white, where iridescent effects produce only other colours. The term pearlescent is used to describe certain paint finishes, usually in the automotive industry, which actually produce iridescent effects.

Soap Bubble - foliage background - iridescent colours - Traquair 040801
Iridescence in soap bubbles

Etymology

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".[1] 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".

Mechanisms

Dieselrainbow
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.
Iridescent biofilm on a fishtank
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 with the angle of observation and the angle of illumination.[2][3] 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).[2][4] 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,[5][6] or a wide range of colours can be observed.[7]

Iridescence can also be created by diffraction. This is found in items like CDs, DVDs, some types of prisms, or cloud iridescence.[8] 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 gratings 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.[9] 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 coloration due to plant pigments.[10][11][12]

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.[13] 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.[14][15] It was later found that iridescence in the peacock is due to a complex photonic crystal.[16]

Pearlescence

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 all of the light is white.[17] Artificial pigments and paints showing an iridescent effect are often described as pearlescent, for example when used for car paints.[18]

Examples

Arthropods and molluscs:

Female Golden Stag Beetle

The iridescent exoskeleton of a golden stag beetle

Haliotis iris LC0283

The inside surface of Haliotis iris, the paua shell

Tachinidae

Structurally coloured wings of a Tachinid fly

Chordates:
The feathers of birds such as kingfishers,[19] birds-of-paradise,[20] hummingbirds, parrots, starlings,[21] grackles, ducks, and peacocks[16] are iridescent. The lateral line on the neon tetra is also iridescent.[5] A single iridescent species of gecko, Cnemaspis kolhapurensis, was identified in India in 2009.[22] The tapetum lucidum, present in the eyes of many vertebrates, is also iridescent.[23]

Peacock 2

Both the body and the train of the peacock are iridescent

Iridescent begonia
Iridescent Begonia leaf

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.[24][25]

Meat:

Meat Iridiscence

Iridescence in meat, caused by light diffraction on the exposed muscle cells[26]

Minerals and compounds:

Wismut Kristall und 1cm3 Wuerfel

A bismuth crystal with a thin iridescent layer of bismuth oxide

Engine oil rainbow p1120058

An engine oil spill

Man-made objects:

Pearlescent Toyota Supra - 002

Pearlescent paint job on a Toyota Supra car

CD-ROM

Playing surface of a compact disc

Glitter nail polish (purple)

iridescent glitter nail polish

Nanocellulose is sometimes iridescent,[27] as are thin films of gasoline and some other hydrocarbons and alcohols when floating on water.[28]

To create jewelry with crystal glass that lets light refract in a rainbow spectrum, Swarovski coats some of its products with special metallic chemical coatings and for example his Aurora Borealis gives the surface a rainbow appearance.

See also

References

  1. ^ "Online Etymology Dictionary". etymonline.com. Archived from the original on 2014-04-07.
  2. ^ a b Nano-optics in the biological world: beetles, butterflies, birds and moths Archived 2014-09-09 at the Wayback Machine Srinivasarao, M. (1999) Chemical Reviews pp: 1935–1961
  3. ^ Physics of structural colours Archived 2015-02-13 at the Wayback Machine Kinoshita, S. et al (2008) Rep. Prog. Phys. 71: 076401
  4. ^ Meadows M.; et al. (2009). "Iridescence: views from many angles". J. R. Soc. Interface. 6: S107–S113. doi:10.1098/rsif.2009.0013.focus. PMC 2706472. PMID 19336343. Archived from the original on 2015-02-15.
  5. ^ a b Yoshioka S.; et al. (2011). "Mechanism of variable structural colour in the neon tetra: quantitative evaluation of the Venetian blind model". J. Royal Soc. Interface. 8 (54): 56–66. doi:10.1098/rsif.2010.0253. PMC 3024824. PMID 20554565.
  6. ^ Rutowski RL; et al. (2005). "Pterin pigments amplify iridescent ultraviolet signal in males of the orange sulphur butterfly, Colias eurytheme". Proc. R. Soc. B. 272 (1578): 2329–2335. doi:10.1098/rspb.2005.3216. PMC 1560183. PMID 16191648.
  7. ^ Saego AE; et al. (2009). "Gold bugs and beyond: a review of iridescence and structural colour mechanisms in beetles (Coleoptera)". J. R. Soc. Interface. 6: S165–S184. Archived from the original on 2015-02-15.
  8. ^ 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
  9. ^ Hsiung, Bor-Kai; Siddique, Radwanul Hasan; Stavenga, Doekele G.; Otto, Jürgen C.; Allen, Michael C.; Liu, Ying; Lu, Yong-Feng; Deheyn, Dimitri D.; Shawkey, Matthew D. (2017-12-22). "Rainbow peacock spiders inspire miniature super-iridescent optics". Nature Communications. 8 (1): 2278. doi:10.1038/s41467-017-02451-x. ISSN 2041-1723. PMC 5741626. PMID 29273708.
  10. ^ Nature's palette: the science of plant colour. Lee, DW (2007) University of Chicago Press
  11. ^ Iridescent flowers? Contribution of surface structures to optical signaling Archived 2016-09-24 at the Wayback Machine van der Kooi, CJ et al (2014) New Phytol 203: 667–673
  12. ^ Is floral iridescence a biologically relevant cue in plant–pollinator signaling? Archived 2017-03-05 at the Wayback Machine van der Kooi, CJ et al (2015) New Phytol 205: 18–20
  13. ^ Hsiung, Bor-Kai; Siddique, Radwanul Hasan; Jiang, Lijia; Liu, Ying; Lu, Yongfeng; Shawkey, Matthew D.; Blackledge, Todd A. (2017-01-15). "Tarantula-Inspired Noniridescent Photonics with Long-Range Order". Advanced Optical Materials. 5 (2): 1600599. doi:10.1002/adom.201600599. ISSN 2195-1071.
  14. ^ Hooke, Robert. Micrographia. Chapter 36 ('Observ. XXXVI. Of Peacoks, Ducks, and Other Feathers of Changeable Colours.')
  15. ^ Ball, Philip (May 2012). "Nature's Color Tricks". Scientific American. 306 (5): 74–79. doi:10.1038/scientificamerican0512-74. PMID 22550931.
  16. ^ a b Zi J; et al. (2003). "Coloration strategies in peacock feathers". Proc. Natl. Acad. Sci. 100 (22): 12576–12578. doi:10.1073/pnas.2133313100. PMC 240659. PMID 14557541.
  17. ^ Ruth Johnston-Feller (2001). Color Science in the Examination of Museum Objects: Nondestructive Procedures. Getty Publications. pp. 169–. ISBN 978-0-89236-586-9.
  18. ^ Paint and Coating Testing Manual. ASTM International. pp. 229–. GGKEY:7W7C2G88G2J.
  19. ^ Stavenga D.G.; et al. (2011). "Kingfisher feathers – colouration by pigments, spongy nanostructures and thin films". J. Exp. Biol. 214 (23): 3960–3967. doi:10.1242/jeb.062620. PMID 22071186.
  20. ^ Stavenga D.G.; et al. (2010). "Dramatic colour changes in a bird of paradise caused by uniquely structured breast feather barbules". Proc. R. Soc. B. 278 (1715): 2098–2104. doi:10.1098/rspb.2010.2293. PMC 3107630. PMID 21159676.
  21. ^ Plumage Reflectance and the Objective Assessment of Avian Sexual Dichromatism Cuthill, I.C. et al. (1999) Am. Nat. 153: 183-200 JSTOR 303160
  22. ^ "New lizard species found in India". BBC Online. 24 July 2009. Retrieved 20 February 2014.
  23. ^ Engelking, Larry (2002). Review of Veterinary Physiology. Teton NewMedia. p. 90. ISBN 978-1-893441-69-9.
  24. ^ Glover, Beverley J.; Whitney, Heather M. (April 2010). "Structural colour and iridescence in plants: the poorly studied relations of pigment colour". Annals of Botany. 105 (4): 505–511. doi:10.1093/aob/mcq007. PMC 2850791. PMID 20142263.
  25. ^ Graham, Rita M.; Lee, David W.; Norstog, Knut (1993). "Physical and Ultrastructural Basis of Blue Leaf Iridescence in Two Neotropical Ferns". American Journal of Botany. 80 (2): 198–203. doi:10.2307/2445040. JSTOR 2445040.
  26. ^ Martinez-Hurtado, Juan; Akram, Muhammad; Yetisen, Ali (2013). "Iridescence in Meat Caused by Surface Gratings". Foods. 2 (4): 499–506. doi:10.3390/foods2040499. PMC 5302279. PMID 28239133.
  27. ^ Picard, G.; Simon, D.; Kadiri, Y.; LeBreux, J. D.; Ghozayel, F. (2012). "Cellulose Nanocrystal Iridescence: A New Model". Langmuir. 28 (41): 14799–14807. doi:10.1021/la302982s. PMID 22988816.
  28. ^ Zitzewitz, Paul W (2011). The Handy Physics Answer Book. Visible Ink Press. p. 215. ISBN 978-1-57859-357-6.

External links

Ammolite

Ammolite is an opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of North America. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral contained in nacre, with a microstructure inherited from the shell. It is one of few biogenic gemstones; others include amber and pearl.1 In 1981, ammolite was given official gemstone status by the World Jewellery Confederation (CIBJO), the same year commercial mining of ammolite began. It was designated the official gemstone of the City of Lethbridge, Alberta in 2007.Ammolite is also known as aapoak (Kainah for "small, crawling stone"), gem ammonite, calcentine, and Korite. The latter is a trade name given to the gemstone by the Alberta-based mining company Korite. Marcel Charbonneau and his business partner Mike Berisoff were the first to create commercial doublets of the gem in 1967. They went on to form Ammolite Minerals Ltd.

Brockhampton (band)

Brockhampton (stylized in all caps) is an American rap collective formed in San Marcos, Texas, in 2015 and currently based in California. Led by Kevin Abstract, Brockhampton formed partially through the online forum "KanyeToThe", and define themselves as a boy band. In specifically labeling themselves in this way, as the members have repeatedly emphasized in interviews and on social media, they aim to redefine the word, as their style does not fit neatly into the "boy band stereotype". Complex magazine describes the group as "gay, black, white, DIY, ambitious, all-inclusive, and would-be pop stars," and this diversity is what largely distinguishes their lyrics and sound. The group consists of vocalists Kevin Abstract, Matt Champion, Merlyn Wood, and Dom McLennon, vocalists/producers Joba and Bearface, and producers Romil Hemnani, Jabari Manwa, and Kiko Merley (the latter two of which function as the duo Q3), as well as graphic designer Henock "HK" Sileshi, photographer Ashlan Grey, web designer Roberto Ontenient (who also features prominently in voice skits), and manager Jon Nunes.

The group released their first mixtape All-American Trash in 2016. Their debut studio album, Saturation, was released on June 9, 2017, followed by Saturation II on August 25 and Saturation III on December 15. On March 30, 2018, Brockhampton announced that they had signed a record deal under the label

RCA Records. Their fourth studio album, Iridescence, was released on September 21, 2018 and debuted at No. 1 on the Billboard 200 album chart. The album is also the first in their second trilogy, known as "The Best Years of Our Lives".

Christmas beetle

Christmas beetle is a name commonly applied to the Australian and South African beetle genus Anoplognathus. They are known as Christmas beetles because they are abundant in both urban and rural areas close to Christmas. Christmas beetles are large (20–30 mm long) members of the scarab family that are noisy and clumsy fliers, similar to the cockchafers of Europe. They typically have elytra that are a dark or light brown, or green, while some species have a green-yellow iridescence.

The genus includes 35 species, several of which have been implicated in dieback of eucalypts. Anoplognathus pallidicollis is the species most commonly observed and associated with the name of Christmas beetle. However, there is a tendency for the name Christmas beetle to be used more ambiguously to refer to other metallic beetles not in this family, such as the stag beetle genus Lamprima.

Cloud iridescence

Cloud iridescence or irisation is a colorful optical phenomenon that occurs in a cloud and appears in the general proximity of the Sun or Moon. The colors resemble those seen in soap bubbles and oil on a water surface. It is a type of photometeor. This fairly common phenomenon is most often observed in altocumulus, cirrocumulus, lenticular, and cirrus clouds. They sometimes appear as bands parallel to the edge of the clouds. Iridescence is also seen in the much rarer polar stratospheric clouds, also called nacreous clouds.The colors are usually pastel, but can be very vivid or mingled together, sometimes similar to mother-of-pearl. When appearing near the Sun, the effect can be difficult to spot as it is drowned in the Sun's glare. This may be overcome by shielding the sunlight with one's hand or hiding it behind a tree or building. Other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water.

Death Valley '69

"Death Valley '69" is a song by American alternative rock band Sonic Youth and featuring Lydia Lunch. The song was written and sung by Thurston Moore and fellow New York musician Lunch, and recorded by Martin Bisi in 1984. A demo version of the song was released in December 1984 on Iridescence Records. A re-recorded version was released in EP format with different artwork in June 1985; this version was featured on their second studio album, Bad Moon Rising.

Gonepteryx rhamni

Gonepteryx rhamni (known as the common brimstone) is a butterfly of the family Pieridae. It lives throughout the Palearctic zone and is commonly found across Europe, Asia, and North Africa. Across much of its range, it is the only species of its genus, and is therefore simply known locally as the brimstone.

The brimstone relies on two species of buckthorn plants as host plants for its larvae; this influences its geographic range and distribution, as these plants are commonly found in wetlands. The adult brimstone travels to woodland areas to spend seven months overwintering. In spring when their host plants have developed, they return to the wetlands to breed and lay eggs. Both the larval and adult forms of the common brimstone have protective coloration and behaviour that decreases their chances of being recognised and subsequently preyed upon.The adult common brimstone has sexual dimorphism in its wing coloration: males have yellow wings and iridescence while females have greenish-white wings and are not iridescent. This iridescence is affected by environmental factors.

Iridescence (album)

Iridescence (stylized in all lowercase) is the fourth studio album by American boy band Brockhampton, released on September 21, 2018 by Question Everything, Inc. RCA Records. It is their major-label debut and is supposedly the first installment of their The Best Years of Our Lives trilogy, however no future installments in this trilogy have been announced as of 2019. The self-produced album was recorded at Abbey Road Studios in London, as well as the group's own studio in Hawaii. It is their first album since rapper Ameer Vann's departure from the group following sexual misconduct allegations. It debuted at number one on the US Billboard 200 albums chart, becoming the group's first chart-topping album.

Iridescent shark

The iridescent shark (Pangasianodon hypophthalmus) is a species of shark catfish (family Pangasiidae) native to the rivers of Southeast Asia. Despite its name, it is not a shark. It is found in the Mekong basin as well as the Chao Phraya River, and is heavily cultivated for food there.

The meat is often marketed under the common name swai. It has also been introduced into other river basins as a food source, and its striking appearance and iridescence have made it popular with fishkeeping hobbyists, among whom it is also known as the Siamese shark or sutchi catfish. The swai's omnivorous diet consists of crustaceans, other fish, and plant matter.

Key West quail-dove

The Key West quail-dove (Geotrygon chrysia) is a species of bird from the doves and pigeon family Columbidae. It is probably most closely related to the bridled quail-dove.The Key West quail-dove breeds in the Bahamas and, except for Jamaica, throughout the Greater Antilles. It formerly bred in the Florida Keys and southernmost mainland Florida. It was discovered on Key West and that is how the bird received its name. Although no longer breeding in Florida, it occasionally is still recorded in the Keys and southernmost mainland Florida as a vagrant. It lays two buff-colored eggs on a flimsy platform built on a shrub. Some nests are built on the ground.The Key West quail-dove is approximately 27–31 cm in length. The bird is distinguished by having a dark rust-colored back and similarly colored wings. It has some amethyst or bronze green iridescence on its crown, nape and in the back of its neck. The mantle, back, rump and inner wing coverts show some purplish red iridescence. It also has a bold white facial stripe. Its call is similar that of the white-tipped dove.This bird is found in tropical and subtropical dry forests, shrublands, and lowland moist forests. These birds forage on the ground, mainly eating seeds, berries and fallen fruit. It is fond of poisonwood fruit. It will also take snails in its diet.

Lusterware

Lusterware or Lustreware (respectively the US and all other English spellings) is a type of pottery or porcelain with a metallic glaze that gives the effect of iridescence, produced by metallic oxides in an overglaze finish, which is given a second firing at a lower temperature in a "muffle kiln", reduction kiln, which excludes oxygen.

Lustre (mineralogy)

Lustre or luster is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin lux, meaning "light", and generally implies radiance, gloss, or brilliance.

A range of terms are used to describe lustre, such as earthy, metallic, greasy, and silky. Similarly, the term vitreous (derived from the Latin for glass, vitrum) refers to a glassy lustre. A list of these terms is given below.

Lustre varies over a wide continuum, and so there are no rigid boundaries between the different types of lustre. (For this reason, different sources can often describe the same mineral differently. This ambiguity is further complicated by lustre's ability to vary widely within a particular mineral species.) The terms are frequently combined to describe intermediate types of lustre (for example, a "vitreous greasy" lustre).

Some minerals exhibit unusual optical phenomena, such as asterism (the display of a star-shaped luminous area) or chatoyancy (the display of luminous bands, which appear to move as the specimen is rotated). A list of such phenomena is given below.

Nacre

Nacre ( NAY-kər also NAK-rə), also known as mother of pearl, is an organic-inorganic composite material produced by some molluscs as an inner shell layer; it also makes up the outer coating of pearls. It is strong, resilient, and iridescent.

Nacre is found in some of the most ancient lineages of bivalves, gastropods, and cephalopods. However, the inner layer in the great majority of mollusc shells is porcellaneous, not nacreous, and this usually results in a non-iridescent shine, or more rarely in non-nacreous iridescence such as flame structure as is found in conch pearls.

The outer layer of pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre. Other mollusc families that have a nacreous inner shell layer include marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.

Oligoclase

Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite (NaAlSi3O8) and anorthite (CaAl2Si2O8). The albite:anorthite molar ratio ranges from 90:10 to 70:30.

Oligoclase is a high sodium feldspar crystallizing in the triclinic system. The Mohs hardness is 6 to 6.5 and the specific gravity is 2.64 to 2.66. The refractive indices are: nα=1.533–1.543, nβ=1.537–1.548, and nγ=1.542–1.552. In color it is usually white, with shades of grey, green, or red.

Opalescence

Opalescence refers to the optical phenomena displayed by the mineraloid gemstone opal (hydrated silicon dioxide). However, there are three notable types of opal (precious, common, and fire), each with different optical effects, so the intended meaning varies depending on context. The optical effects seen in various types of opal are a result of refraction (precious and fire) or reflection (common) due to the layering, spacing, and size of the myriad microscopic silicon dioxide spheres and included water (or air) in its physical structure. When the size and spacing of the silica spheres are relatively small, refracted blue-green colors are prevalent; when relatively larger, refracted yellow-orange-red colors are seen; and when larger yet, reflection yields a milky-hazy sheen.Precious Opal. The general definition of opalescent is a milky iridescence (iridescence) displayed by an opal which describes the visual effect of precious opal very well, and opalescence is commonly used in lay terms as a synonym for iridescence.Common Opal. In contrast, common opal does not display a iridescence but often exhibits a hazy sheen of light from within the stone--the phenomenon that gemologists define strictly as opalescence. This milky sheen displayed by opal is a form of adularescence.Fire Opal is a relatively transparent gemstone with a vivid yellow-orange-red color and rarely displays iridescence.

In a physical sense, some cases of opalescence could be related to a type of dichroism seen in highly dispersed systems with little opacity. Due to Rayleigh scattering, a transparent material appears yellowish-red in transmitted white light and blue in the scattered light perpendicular to the transmitted light. The phenomenon illustrated in the bottom photo is an example of the Tyndall effect.

Peafowl

Peafowl is a common name for three species of birds in the genera Pavo and Afropavo of the Phasianidae family, the pheasants and their allies. Male peafowl are referred to as peacocks, and female peafowl as peahens. The two Asiatic species are the blue or Indian peafowl originally of the Indian subcontinent, and the green peafowl of Southeast Asia; the one African species is the Congo peafowl, native only to the Congo Basin. Male peafowl are known for their piercing calls and their extravagant plumage. The latter is especially prominent in the Asiatic species, which have an eye-spotted "tail" or "train" of covert feathers, which they display as part of a courtship ritual.

The functions of the elaborate iridescent colouration and large "train" of peacocks have been the subject of extensive scientific debate. Charles Darwin suggested they served to attract females, and the showy features of the males had evolved by sexual selection. More recently, Amotz Zahavi proposed in his handicap theory that these features acted as honest signals of the males' fitness, since less-fit males would be disadvantaged by the difficulty of surviving with such large and conspicuous structures.

Polar stratospheric cloud

Polar stratospheric clouds (PSCs) are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 m (49,000–82,000 ft). They are best observed during civil twilight, when the Sun is between 1 and 6 degrees below the horizon, as well as in winter and in more northerly latitudes. One main type of PSC is made up mostly of supercooled droplets of water and nitric acid and is implicated in the formation of ozone holes. The other main type consists only of frozen ice crystals and is not considered harmful. This type of PSC is also referred to as nacreous (, from nacre, or mother of pearl, due to its iridescence).

Snakeskin

Snakeskin may either refer to the skin of a live snake, the shed skin of a snake after molting, or to a type of leather that is made from the hide of a dead snake.

Structural coloration

In living creatures, structural coloration is the production of colour by microscopically structured surfaces fine enough to interfere with visible light, sometimes in combination with pigments. For example, peacock tail feathers are pigmented brown, but their microscopic structure makes them also reflect blue, turquoise, and green light, and they are often iridescent.

Structural coloration was first observed by English scientists Robert Hooke and Isaac Newton, and its principle – wave interference – explained by Thomas Young a century later. Young described iridescence as the result of interference between reflections from two or more surfaces of thin films, combined with refraction as light enters and leaves such films. The geometry then determines that at certain angles, the light reflected from both surfaces interferes constructively, while at other angles, the light interferes destructively. Different colours therefore appear at different angles.

In animals such as on the feathers of birds and the scales of butterflies, interference is created by a range of photonic mechanisms, including diffraction gratings, selective mirrors, photonic crystals, crystal fibres, matrices of nanochannels and proteins that can vary their configuration. Some cuts of meat also show structural coloration due to the exposure of the periodic arrangement of the muscular fibres. Many of these photonic mechanisms correspond to elaborate structures visible by electron microscopy. In the few plants that exploit structural coloration, brilliant colours are produced by structures within cells. The most brilliant blue coloration known in any living tissue is found in the marble berries of Pollia condensata, where a spiral structure of cellulose fibrils produces Bragg's law scattering of light. The bright gloss of buttercups is produced by thin-film reflection by the epidermis supplemented by yellow pigmentation, and strong diffuse scattering by a layer of starch cells immediately beneath.

Structural coloration has potential for industrial, commercial and military application, with biomimetic surfaces that could provide brilliant colours, adaptive camouflage, efficient optical switches and low-reflectance glass.

Troides magellanus

Troides magellanus, the Magellan birdwing, is a large and striking birdwing butterfly found in the Philippines and on Taiwan's Orchid Island.

This butterfly is named for the explorer Ferdinand Magellan who was killed in the Philippines in 1521.

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