Purple in science and nature

Purple is a color intermediate between blue and red. It is similar to violet, but unlike violet, which is a spectral color with its own wavelength on the visible spectrum of light, purple is a composite color made by combining red and blue. According to surveys in Europe and the U.S., purple is the color most often associated with royalty, magic, mystery, and piety. When combined with pink, it is associated with eroticism, femininity, and seduction.

Purple was the color worn by Roman magistrates; it became the imperial color worn by the rulers of the Byzantine Empire and the Holy Roman Empire, and later by Roman Catholic bishops. Similarly in Japan, the color is traditionally associated with the Emperor and aristocracy. The complementary color of purple is yellow.

Etymology and definitions
The word ‘purple’ comes from the Old English word purpul which derives from Latin purpura, in turn from the Greek πορφύρα (porphura), name of the Tyrian purple dye manufactured in classical antiquity from a mucus secreted by the spiny dye-murex snail.

The first recorded use of the word ‘purple’ in the English language was in the year 975 AD. In heraldry, the word purpure is used for purple.

Purple vs. violet

Color coordinates
Hex triplet #800080
RGB (r, g, b) (128, 0, 128)
CMYK (c, m, y, k) (50, 100, 0, 0)
HSV (h, s, v) (300°, 100%, 50%)

Color coordinates
Hex triplet #8F00FF
sRGBB (r, g, b) (143, 0, 255)
CMYKH (c, m, y, k) (44, 100, 0, 0)
HSV (h, s, v) (274°, 100%, 100%)

In the traditional color wheel used by painters, violet and purple are both placed between red and blue. Purple occupies the space closer to red, between crimson and violet. Violet is closer to blue, and is usually less saturated than purple.

While the two colors look similar, from the point of view of optics there are important differences. Violet is a spectral color – it occupies its own place at the end of the spectrum of light first identified by Isaac Newton in 1672, and it has its own wavelength (approximately 380–420 nm) – whereas purple is a combination of two spectral colors, red and blue. There is no such thing as the “wavelength of purple light”; it only exists as a combination. See Line of purples.

Monochromatic violet light cannot be produced by the red-green-blue (RGB) color system, the method used to create colors on a television screen or computer display. (In fact, the only monochromatic colors of light that can be produced by this color system are the red, green, and blue that define it.) However, the system is capable of approximating it due to the fact that the L-cone (red cone) in the eye is uniquely sensitive to two different discontinuous regions in the visible spectrum – its primary region being the long wavelength light of the yellow-red region of the spectrum, and a secondary smaller region overlapping with the S-cone (blue cone) in the shortest wavelength, violet part. This means that when violet light strikes the eye, the S-cone should be stimulated strongly, and the L-cone stimulated weakly along with it. By lighting the red primary of the display weakly along with the blue primary, a relatively similar pattern of sensitization can be achieved, creating an illusion, the sensation of extremely short wavelength light using what is in fact mixed light of two longer wavelengths. The resulting color has the same hue as pure violet; however, it has a lower saturation.

One psychophysical difference between purple and violet is their appearance with an increase in luminance (apparent brightness). Violet, as it brightens, looks more and more blue. The same effect does not happen with purple. This is the result of what is known as the Bezold–Brücke shift.

While the scientific definitions of violet and purple are clear, the cultural definitions are more varied. The color known in antiquity as Tyrian purple ranged from crimson to a deep bluish-purple, depending upon how it was made. In France, purple is defined as “a dark red, inclined toward violet”. The color called purple by the French, pourpre, contains more red and half the amount of blue of the color called purple in the United States and the U.K. In German, this color is sometimes called Purpurrot (“purple-red”) to avoid confusion.

In science and nature

The optics of purple
Purple, unlike violet, is not one of the colors of the visible spectrum. It was not one of the colors of the rainbow identified by Isaac Newton, and it does not have its own wavelength of light. For this reason, it is called a non-spectral color. It exists in culture and art, but not, in the same way that violet does, in optics. It is simply a combination, in various proportions, of two primary colors, red and blue.

In color theory, a “purple” is defined as any non-spectral color between violet and red (excluding violet and red themselves). The spectral colors violet and indigo are not purples according to color theory, but they are purples according to common English usage since they are between red and blue.

In the traditional color wheel long used by painters, purple is usually placed between crimson and violet. In a slightly different variation, on the color wheel, it is placed between magenta and violet. This shade is sometimes called electric purple (See Shades of purple).

In the RGB color model, named for the colors red, green, and blue, used to create all the colors on a computer screen or television, the range of purples is created by mixing red and blue light of different intensities on a black screen. The standard HTML color purple is created by red and blue light of equal intensity, at a brightness that is halfway between full power and darkness.

In color printing, purple is sometimes represented by the color magenta, or sometimes by mixing magenta with red or blue. It can also be created by mixing just red and blue alone, but in that case the purple is less bright, with lower saturation or intensity. A less bright purple can also be created with light or paint by adding a certain quantity of the third primary color (green for light or yellow for pigment).

On a chromaticity diagram, the straight line connecting the extreme spectral colors (red and violet) is known as the line of purples (or ‘purple boundary’); it represents one limit of human color perception. The color magenta used in the CMYK printing process is near the center of the line of purples, but most people associate the term “purple” with a somewhat bluer tone, such as is displayed by the color “electric purple” (a color also directly on the line of purples), shown below. Some common confusion exists concerning the color names “purple” and “violet”. Purple is a mixture of red and blue light, whereas violet is a spectral color.

On the CIE xy chromaticity diagram, violet is on the curved edge in the lower left, while purples are on the straight line connecting the extreme colors red and violet; this line is known as the line of purples, or the purple line.

Related Post

Hematite and manganese are the oldest pigments used for the color purple. They were used by Neolithic artists in the form of sticks, like charcoal, or ground and powdered and mixed with fat, and used as a paint. Hematite is a reddish iron oxide which, when ground coarsely, makes a purple pigment. Manganese was also used in Roman times to color glass purple.
Han purple was the first synthetic purple pigment, invented in China in about 700 BC. It was used in wall paintings and pottery and other applications. In color, it was very close to indigo, which had a similar chemical structure. Han purple was very unstable, and sometimes was the result of the chemical breakdown of Han blue.
During the Middle Ages, artists usually made purple by combining red and blue pigments; most often blue azurite or lapis-lazuili with red ochre, cinnabar, or minium. They also combined lake colors made by mixing dye with powder; using woad or indigo dye for the blue, and dye made from cochineal for the red.

Cobalt violet was the first modern synthetic color in the purple family, manufactured in 1859. It was found, along with cobalt blue, in the palette of Claude Monet, Paul Signac, and Georges Seurat. It was stable, but had low tinting power and was expensive, so quickly went out of use.
Manganese violet was a stronger color than cobalt violet, and replaced it on the market.
Quinacridone violet, one of a modern synthetic organic family of colors, was discovered in 1896 but not marketed until 1955. It is sold today under a number of brand names.

The most famous purple dye in the ancient world was Tyrian purple, made from a type of sea snail called the murex, found around the Mediterranean. (See history section above).

In western Polynesia, residents of the islands made a purple dye similar to Tyrian purple from the sea urchin. In Central America, the inhabitants made a dye from a different sea snail, the purpura, found on the coasts of Costa Rica and Nicaragua. The Mayans used this color to dye fabric for religious ceremonies, while the Aztecs used it for paintings of ideograms, where it symbolized royalty.

In the Middle Ages, those who dyed blue fabric and red fabric were members of different guilds, and were forbidden to dye any other colors than those of their own guild. Most purple fabric was made by the dyers who worked with red, and who used dye from madder or cochineal, so Medieval violet colors were inclined toward red.

Orcein, or purple moss, was another common purple dye. It was known to the ancient Greeks and Hebrews, and was made from a Mediterranean lichen called archil or dyer’s moss (Roccella tinctoria), combined with an ammoniac, usually urine. Orcein began to achieve popularity again in the 19th century, when violet and purple became the color of demi-mourning, worn after a widow or widower had worn black for a certain time, before he or she returned to wearing ordinary colors.

From the Middle Ages onward, purple and violet dyes for the clothing of common people were often made from the blackberry or other red fruit of the genus rubus, or from the mulberry. All of these dyes were more reddish than bluish, and faded easily with washing and exposure to sunlight.

A popular new dye which arrived in Europe from the New World during the Renaissance was made from the wood of the logwood tree (Haematoxylum campechianum), which grew in Spanish Mexico. Depending on the different minerals added to the dye, it produced a blue, red, black or, with the addition of alum, a purple color, It made a good color, but, like earlier dyes, it did not resist sunlight or washing.

In the 18th century, chemists in England, France and Germany began to create the first synthetic dyes. Two synthetic purple dyes were invented at about the same time. Cudbear is a dye extracted from orchil lichens that can be used to dye wool and silk, without the use of mordant. Cudbear was developed by Dr Cuthbert Gordon of Scotland: production began in 1758, The lichen is first boiled in a solution of ammonium carbonate. The mixture is then cooled and ammonia is added and the mixture is kept damp for 3–4 weeks. Then the lichen is dried and ground to powder. The manufacture details were carefully protected, with a ten-feet high wall being built around the manufacturing facility, and staff consisting of Highlanders sworn to secrecy.

French purple was developed in France at about the same time. The lichen is extracted by urine or ammonia. Then the extract is acidified, the dissolved dye precipitates and is washed. Then it is dissolved in ammonia again, the solution is heated in air until it becomes purple, then it is precipitated with calcium chloride; the resulting dye was more solid and stable than other purples.

Cobalt violet is a synthetic pigment that was invented in the second half of the 19th century, and is made by a similar process as cobalt blue, cerulean blue and cobalt green. It is the violet pigment most commonly used today by artists.

Mauveine, also known as aniline purple and Perkin’s mauve, was the first synthetic organic chemical dye, discovered serendipitously in 1856. Its chemical name is 3-amino-2,±9-dimethyl-5-phenyl-7-(p-tolylamino)phenazinium acetate.

Fuchsine was another synthetic dye made shortly after mauveine. It produced a brilliant fuchsia color.

In the 1950s, a new family of purple and violet synthetic organic pigments called quinacridone came onto the market. It had originally been discovered in 1896, but were not synthetized until 1936, and not manufactured until the 1950s. The colors in the group range from deep red to bluish purple in color, and have the molecular formula C20H12N2O2. They have strong resistance to sunlight and washing, and are widely used today in oil paints, water colors, and acrylics, as well as in automobile coatings and other industrial coatings.

Why grapes, eggplants and pansies are purple
Grapes, eggplants, pansies and other fruits, vegetables and flowers are purple because they contain natural pigments called anthocyanins. These pigments are found in the leaves, roots, stems, vegetables, fruits and flowers of all plants. They aid photosynthesis by blocking harmful wavelengths of light that would damage the leaves. In flowers, the purple anthocyanins help attract insects who pollinate the flowers. Not all anthocyanins are purple; they vary in color from red to purple to blue, green, or yellow, depending upon the level of their pH.

Purple bacteria are proteobacteria that are phototrophic, that is, capable of producing energy through photosynthesis.
In April 2007 it was suggested that early archaea may have used retinal, a purple pigment, instead of chlorophyll, to extract energy from the sun. If so, large areas of the ocean and shoreline would have been colored purple; this is called the Purple Earth hypothesis.
One of the stars in the Pleiades, called Pleione, is sometimes called Purple Pleione because, being a fast spinning star, it has a purple hue caused by its blue-white color being obscured by a spinning ring of electrically excited red hydrogen gas.
The Purple Forbidden enclosure is a name used in traditional Chinese astronomy for those Chinese constellations that surround the North Celestial Pole.
Purple Mountain in China is located on the eastern side of Nanjing, Jiangsu Province, People’s Republic of China. Its peaks are often found enveloped in purple clouds at dawn and dusk, hence comes its name “Purple Mountain”. The Purple Mountain Observatory is located there.
Purple Mountain in County Kerry, Ireland, takes its name from the color of the shivered slate on its summit.
Purple Mountain in Wyoming (el. 8,392 feet (2,558 m) is a mountain peak in the southern section of the Gallatin Range in Yellowstone National Park.
Purple Mountain, Alaska
Purple Mountain, Oregon
Purple Mountain, Washington
Purple Peak, Colorado

Why distant mountains look blue or purple
The greater the distance from the eye to mountains, the lighter and more blue they appear. This effect, long recognized by Leonardo da Vinci and other painters, is called aerial perspective or atmospheric perspective. The more distant the mountains are, the less contrast the eye sees between the mountains and the sky.

The bluish color is caused by an optical effect called Rayleigh scattering. The sunlit sky is blue because air scatters short-wavelength light more than longer wavelengths. Since blue light is at the short wavelength end of the visible spectrum, it is more strongly scattered in the atmosphere than long wavelength red light. The result is that the human eye perceives blue when looking toward parts of the sky other than the sun.

At sunrise and sunset, the light is passing through the atmosphere at a lower angle, and traveling a greater distance through a larger volume of air. Much of the green and blue is scattered away, and more red light comes to the eye, creating the colors of the sunrise and sunset and making the mountains look purple.

Source From Wikipedia