Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear Gradient to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in or thin films. Examples of iridescence include , , butterfly wings and seashell nacre, and minerals such as opal. 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 word ἶρις
îris (
Genitive ἴριδος
íridos), meaning
rainbow, and is combined with the Latin suffix
-escent, meaning "having a tendency toward".
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
Iridescence is an optical phenomenon of surfaces in which
hue changes with the angle of observation and the angle of 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.
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,
Iridescence can also be created by diffraction. This is found in items like CDs, DVDs, some types of prisms, or cloud iridescence.
In biological (and biomimetic) uses, colours produced other than with or are called structural colouration. 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.[Hooke, Robert. Micrographia. Chapter 36 ('Observ. XXXVI. Of Peacoks, Ducks, and Other Feathers of Changeable Colours.')]
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 most of the light is white, giving the object a
pearl-like luster.
Artificial pigments and paints showing an iridescent effect are often described as pearlescent, for example when used for
.
Examples
Life
Invertebrates
Eledone moschata has a bluish iridescence running along its body and
Tentacle.
Vertebrates
The
of birds such as
,
birds-of-paradise,
,
,
,
,
, and
are iridescent. The lateral line on the
neon tetra is also iridescent.
A single iridescent species of gecko,
Cnemaspis kolhapurensis, was identified in India in 2009.
The
tapetum lucidum, present in the
of many vertebrates, is also iridescent.
Iridescence is known to be present among prehistoric non-avian and avian dinosaurs such as
Dromaeosauridae,
enantiornithes, and
Lithornithidae.
Muscle tissues can display irisdescence.
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
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.
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
Non-biological
Minerals
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
Meteorological
File:Polar Stratospheric Clouds.jpg|Polar stratospheric clouds displaying a Nacreous iridescence
File:Irid clouds1.jpg|Cloud iridescence
Human-made
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
File:1899 reverse.jpg|Iridescent 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 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.
Nanocellulose is sometimes iridescent,
See also
External links
