Dye

A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber.[2]

Both dyes and pigments are colored, because they absorb only some wavelengths of visible light. Dyes are usually soluble in water whereas pigments are insoluble. Some dyes can be rendered insoluble with the addition of salt to produce a lake pigment.

Indigo skeletal
Chemical structure of indigo dye, the blue coloration of blue jeans. Once extracted from plants, indigo dye is almost exclusively synthesized industrially.[1]
Conner-prairie-yarn-drying
Yarn drying after being dyed in the early American tradition, at Conner Prairie living history museum.

Natural vs synthetic

Dyeing British Library Royal MS 15.E.iii, f. 269 1482
Dyeing wool cloth, 1482: from a French translation of Bartolomaeus Anglicus

The majority of natural dyes are derived from plant sources: roots, berries, bark, leaves, and wood, fungi, and lichens.[3] Most dyes are synthetic, i.e., are man-made from petrochemicals. Other than pigmentation, they have a range of applications including organic dye lasers,[4] optical media (CD-R) and camera sensors (color filter array).

History

Textile dyeing dates back to the Neolithic period. Throughout history, people have dyed their textiles using common, locally available materials. Scarce dyestuffs that produced brilliant and permanent colors such as the natural invertebrate dyes Tyrian purple and crimson kermes were highly prized luxury items in the ancient and medieval world. Plant-based dyes such as woad, indigo, saffron, and madder were important trade goods in the economies of Asia and Europe. Across Asia and Africa, patterned fabrics were produced using resist dyeing techniques to control the absorption of color in piece-dyed cloth. Dyes from the New World such as cochineal and logwood were brought to Europe by the Spanish treasure fleets[5], and the dyestuffs of Europe were carried by colonists to America.[6]

Dyed flax fibers have been found in the Republic of Georgia in a prehistoric cave dated to 36,000 BP.[7][8] Archaeological evidence shows that, particularly in India and Phoenicia, dyeing has been widely carried out for over 5,000 years. Early dyes were obtained from animal, vegetable or mineral sources, with no to very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, only few of which are used on a commercial scale. The first synthetic dye, mauveine, was discovered serendipitously by William Henry Perkin in 1856.[9][10]

Blick in Farbstoffsammlung 01
Historical collection of over 10,000 dyes at Technical University Dresden, Germany

The discovery of mauveine started a surge in synthetic dyes and in organic chemistry in general. Other aniline dyes followed, such as fuchsine, safranine, and induline. Many thousands of synthetic dyes have since been prepared.[11][12][13]

Types

RITdye
RIT brand dye from mid-20th century Mexico, part of the permanent collection of the Museo del Objeto del Objeto
Hårfärgning - 2007
A woman dying her hair.

Dyes are classified according to their solubility and chemical properties.[2]

Acid dyes are water-soluble anionic dyes that are applied to fibers such as silk, wool, nylon and modified acrylic fibers using neutral to acid dye baths. Attachment to the fiber is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fiber. Acid dyes are not substantive to cellulosic fibers. Most synthetic food colors fall in this category. Examples of acid dye are Alizarine Pure Blue B, Acid red 88, etc.

Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibers, but find some use for wool and silk. Usually acetic acid is added to the dye bath to help the uptake of the dye onto the fiber. Basic dyes are also used in the coloration of paper.

Direct or substantive dyeing is normally carried out in a neutral or slightly alkaline dye bath, at or near boiling point, with the addition of either sodium chloride (NaCl) or sodium sulfate (Na2SO4) or sodium carbonate (Na2CO3). Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.

Mordant dyes require a mordant, which improves the fastness of the dye against water, light and perspiration. The choice of mordant is very important as different mordants can change the final color significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques. The most important mordant dyes are the synthetic mordant dyes, or chrome dyes, used for wool; these comprise some 30% of dyes used for wool, and are especially useful for black and navy shades. The mordant potassium dichromate is applied as an after-treatment. It is important to note that many mordants, particularly those in the heavy metal category, can be hazardous to health and extreme care must be taken in using them.

Vat dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water-soluble alkali metal salt of the dye. This form is often colorless, in which case it is referred to as a Leuco dye, and has an affinity for the textile fibre. Subsequent oxidation reforms the original insoluble dye. The color of denim is due to indigo, the original vat dye.

Reactive dyes utilize a chromophore attached to a substituent that is capable of directly reacting with the fiber substrate. The covalent bonds that attach reactive dye to natural fibers make them among the most permanent of dyes. "Cold" reactive dyes, such as Procion MX, Cibacron F, and Drimarene K, are very easy to use because the dye can be applied at room temperature. Reactive dyes are by far the best choice for dyeing cotton and other cellulose fibers at home or in the art studio.

Disperse dyes were originally developed for the dyeing of cellulose acetate, and are water-insoluble. The dyes are finely ground in the presence of a dispersing agent and sold as a paste, or spray-dried and sold as a powder. Their main use is to dye polyester, but they can also be used to dye nylon, cellulose triacetate, and acrylic fibers. In some cases, a dyeing temperature of 130 °C (266 °F) is required, and a pressurized dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fiber. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding.

Azoic dyeing is a technique in which an insoluble Azo dye is produced directly onto or within the fiber. This is achieved by treating a fiber with both diazoic and coupling components. With suitable adjustment of dyebath conditions the two components react to produce the required insoluble azo dye. This technique of dyeing is unique, in that the final color is controlled by the choice of the diazoic and coupling components. This method of dyeing cotton is declining in importance due to the toxic nature of the chemicals used.

Sulfur dyes are inexpensive dyes used to dye cotton with dark colors. Dyeing is effected by heating the fabric in a solution of an organic compound, typically a nitrophenol derivative, and sulfide or polysulfide. The organic compound reacts with the sulfide source to form dark colors that adhere to the fabric. Sulfur Black 1, the largest selling dye by volume, does not have a well defined chemical structure.

Food dyes

One other class that describes the role of dyes, rather than their mode of use, is the food dye. Because food dyes are classed as food additives, they are manufactured to a higher standard than some industrial dyes. Food dyes can be direct, mordant and vat dyes, and their use is strictly controlled by legislation. Many are azo dyes, although anthraquinone and triphenylmethane compounds are used for colors such as green and blue. Some naturally occurring dyes are also used.

Other important dyes

A number of other classes have also been established, including:

  • Oxidation bases, for mainly hair and fur
  • Laser dyes:rhodamine 6G and coumarin dyes.[14]
  • Leather dyes, for leather
  • Fluorescent brighteners, for textile fibres and paper
  • Solvent dyes, for wood staining and producing colored lacquers, solvent inks, coloring oils, waxes.
  • Contrast dyes, injected for magnetic resonance imaging, are essentially the same as clothing dye except they are coupled to an agent that has strong paramagnetic properties.[15]
  • Mayhems dye, used in water cooling for looks, often rebranded RIT dye

Chromophoric dyes

By the nature of their chromophore, dyes are divided into:[16]

  • Category:Acridine dyes, derivates of acridine
  • Category:Anthraquinone dyes, derivates of anthraquinone
  • Arylmethane dyes
    • Category:Diarylmethane dyes, based on diphenyl methane
    • Category:Triarylmethane dyes, derivates of triphenylmethane
  • Category:Azo dyes, based on -N=N- azo structure
  • Phthalocyanine dyes, derivatives of phthalocyanine
  • Quinone-imine dyes, derivatives of quinone
    • Category:Azin dyes
      • Category:Eurhodin dyes
      • Category:Safranin dyes, derivates of safranin
    • Indamins
    • Category:Indophenol dyes, derivates of indophenol
    • Category:Oxazin dyes, derivates of oxazin
    • Oxazone dyes, derivates of oxazone
    • Category:Thiazine dyes
  • Category:Thiazole dyes
  • Category:Safranin dyes
  • Xanthene dyes
    • Fluorene dyes, derivatives of fluorene
      • Pyronin dyes
    • Category:Fluorone dyes, based on fluorone
      • Category:Rhodamine dyes, derivatives of rhodamine

Pollution

Dyes produced by the textile, printing and paper industries can end up in waste waters and are therefore a potential source of pollution of rivers and waterways[17].

Various porous materials, often used to adsorb harmful chemicals in general, have been specifically tested to remove dyes from aqueous environments, especially those who could combine wide availability, fast kinetics and strong adsorption capacities.[18]

Possible examples include nickel oxide nanoplates[17], clays[19], activated carbons[20], composites of hydroxyapatite with organic substrates [21][22], graphene oxides[23].

See also

References

  1. ^ Elmar Steingruber (2004). "Indigo and Indigo Colorants". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a14_149.pub2.CS1 maint: Uses authors parameter (link)
  2. ^ a b Booth, Gerald (2000). Dyes, General Survey. Wiley-VCH. doi:10.1002/14356007.a09_073.
  3. ^ Burgess, Rebecca (8 November 2017). "Harvesting Color: How to Find Plants and Make Natural Dyes". Artisan Books. Retrieved 8 November 2017 – via Google Books.
  4. ^ Silfvast, William T. (21 July 2008). "Laser Fundamentals". Cambridge University Press. Retrieved 8 November 2017 – via Google Books.
  5. ^ Castillejo, Marta; Moreno, Pablo; Oujja, Mohamed; Radvan, Roxana; Ruiz, Javier (15 August 2008). "Lasers in the Conservation of Artworks: Proceedings of the International Conference Lacona VII, Madrid, Spain, 17 - 21 September 2007". CRC Press. Retrieved 8 November 2017 – via Google Books.
  6. ^ Adrosko, Rita J. (8 November 1971). "Natural Dyes and Home Dyeing (formerly Titled: Natural Dyes in the United States)". Courier Corporation. Retrieved 8 November 2017 – via Google Books.
  7. ^ Balter, M (2009). "Clothes Make the (Hu) Man". Science. 325 (5946): 1329. doi:10.1126/science.325_1329a. PMID 19745126.
  8. ^ Kvavadze, E; Bar-Yosef, O; Belfer-Cohen, A; Boaretto, E; Jakeli, N; Matskevich, Z; Meshveliani, T (2009). "30,000-Year-Old Wild Flax Fibers". Science. 325 (5946): 1359. doi:10.1126/science.1175404. PMID 19745144. Supporting Online Material
  9. ^ Hubner K (2006). "History – 150 Years of mauveine". Chemie in unserer Zeit. 40 (4): 274–275. doi:10.1002/ciuz.200690054.
  10. ^ Anthony S. Travis (1990). "Perkin's Mauve: Ancestor of the Organic Chemical Industry". Technology and Culture. 31 (1): 51–82. doi:10.2307/3105760. JSTOR 3105760.
  11. ^ Hunger, K., ed. (2003). Industrial Dyes. Chemistry, Properties, Applications. Weinheim: Wiley-VCH.
  12. ^ Zollinger, H. (2003). Color Chemistry. Synthesis, Properties and Applications of Organic Dyes and Pigments, 3rd ed. Weinheim: Wiley-VCH.
  13. ^ "Syntheses, Properties, and Applications of Organic Dyes and Pigments".
  14. ^ F. J. Duarte and L. W. Hillman (Eds.), Dye Laser Principles (Academic, New York, 1990).
  15. ^ "patentstorm.us". Patentstorm.us. Retrieved 8 November 2017.
  16. ^ Llewellyn, Bryan D. "Stainsfile - Dye index". Stainsfile.info. Retrieved 8 November 2017.
  17. ^ a b Brindley, Lewis (July 2009). "New solution for dye wastewater pollution". Chemistry World. Retrieved 2018-07-08.
  18. ^ Gupta, V.K. (June 2009). "Application of low-cost adsorbents for dye removal – A review". Journal of Environmental Management. 90 (8): 2313–2342. doi:10.1016/j.jenvman.2008.11.017.
  19. ^ Aguiar, J.E.; Cecilia, J.A.; Tavares, P.A.S.; Azevedo, D.C.S.; Rodríguez Castellón, E.; Lucena, S.M.P.; Silva Junior, I.J. (2017). "Adsorption study of reactive dyes onto porous clay heterostructures". Appl. Clay Sci. 135: 35−44. doi:10.1016/j.clay.2016.09.001.
  20. ^ Maneerung, Thawatchai; Liew, Johan; Dai, Yanjun; Kawi, Sibudjing; Chong, Clive; Wang, Chi-Hwa (2016). "Activated carbon derived from carbon residue from biomass gasification and its application for dye adsorption: Kinetics, isotherms and thermodynamic studies". Bioresour. Technol. 200: 350–359. doi:10.1016/j.biortech.2015.10.047.
  21. ^ "Removal of Congo red dye from aqueous solution with hydroxyapatite/chitosan composite". Chem. Eng. J. 211-212: 336–342. 2012. doi:10.1016/j.cej.2012.09.100.
  22. ^ Guan, Yebin; Cao, Weicheng; Guan, Hanxi; Lei, Xiaohe; Wang, Xiaohong; Tu, Youzhi; Marchetti, Alessandro; Kong, Xueqian (2018). "A novel polyalcohol-coated hydroxyapatite for the fast adsorption of organic dyes". Colloids Surf. A. 548: 85–91.
  23. ^ Yu, S.J.; Wang, X.X.; Ai, Y.J.; Tan, X.L.; Hayat, T.; Hu,, W.P.; Wang, X.K. (2016). "Experimental and theoretical studies on competitive adsorption of aromatic compounds on reduced graphene oxides". J. Mater. Chem. A. 4 (15): 5654–5662. doi:10.1039/C6TA00890A.

Further reading

  • Abelshauser, Werner. German History and Global Enterprise: BASF: The History of a Company (2004) covers 1865 to 2000
  • Beer, John J. The Emergence of the German Dye Industry (1959)
Aniline

Aniline is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Its main use is in the manufacture of precursors to polyurethane and other industrial chemicals. Like most volatile amines, it has the odor of rotten fish. It ignites readily, burning with a smoky flame characteristic of aromatic compounds.

Azo compound

Azo compounds are compounds bearing the functional group diazenyl R−N=N−R′, in which R and R′ can be either aryl or alkyl.

IUPAC defines azo compounds as: "Derivatives of diazene (diimide), HN=NH, wherein both hydrogens are substituted by hydrocarbyl groups, e.g. PhN=NPh azobenzene or diphenyldiazene." The more stable derivatives contain two aryl groups. The N=N group is called an azo group. The name azo comes from azote, the French name for nitrogen that is derived from the Greek ἀ- (a-, "not") + ζωή (zōē, life).

Many textile and leather articles are dyed with azo dyes and pigments.

Cochineal

The cochineal ( KOTCH-ih-NEEL, KOTCH-ih-neel; Dactylopius coccus) is a scale insect in the suborder Sternorrhyncha, from which the natural dye carmine is derived. A primarily sessile parasite native to tropical and subtropical South America through North America (Mexico and the Southwest United States), this insect lives on cacti in the genus Opuntia, feeding on plant moisture and nutrients. The insects are found on the pads of prickly pear cacti, collected by brushing them off the plants, and dried.The insect produces carminic acid that deters predation by other insects. Carminic acid, typically 17-24% of dried insects' weight, can be extracted from the body and eggs, then mixed with aluminium or calcium salts to make carmine dye, also known as cochineal. Today, carmine is primarily used as a colorant in food and in lipstick (E120 or Natural Red 4).

The carmine dye was used in North America in the 15th century for coloring fabrics and became an important export good during the colonial period. After synthetic pigments and dyes such as alizarin were invented in the late 19th century, natural-dye production gradually diminished. Health fears over artificial food additives, however, have renewed the popularity of cochineal dyes, and the increased demand has made cultivation of the insect profitable again, with Peru being the largest exporter. Some towns in the Mexican state of Oaxaca are still working in handmade textiles using this cochineal.Other species in the genus Dactylopius can be used to produce "cochineal extract", and are extremely difficult to distinguish from D. coccus, even for expert taxonomists; that scientific term from the binary nomenclature, and also the vernacular "cochineal insect", may be used (whether intentionally or casually, and whether or not with misleading effect) to refer to other biological species. (The primary biological distinctions between species are minor differences in host plant preferences, along with very different geographic distributions.)

Dye-sensitized solar cell

A dye-sensitized solar cell (DSSC, DSC, DYSC or Grätzel cell) is a low-cost solar cell belonging to the group of thin film solar cells. It is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photoelectrochemical system. The modern version of a dye solar cell, also known as the Grätzel cell, was originally co-invented in 1988 by Brian O'Regan and Michael Grätzel at UC Berkeley and this work was later developed by the aforementioned scientists at the École Polytechnique Fédérale de Lausanne until the publication of the first high efficiency DSSC in 1991. Michael Grätzel has been awarded the 2010 Millennium Technology Prize for this invention.The DSSC has a number of attractive features; it is simple to make using conventional roll-printing techniques, is semi-flexible and semi-transparent which offers a variety of uses not applicable to glass-based systems, and most of the materials used are low-cost. In practice it has proven difficult to eliminate a number of expensive materials, notably platinum and ruthenium, and the liquid electrolyte presents a serious challenge to making a cell suitable for use in all weather. Although its conversion efficiency is less than the best thin-film cells, in theory its price/performance ratio should be good enough to allow them to compete with fossil fuel electrical generation by achieving grid parity. Commercial applications, which were held up due to chemical stability problems, are forecast in the European Union Photovoltaic Roadmap to significantly contribute to renewable electricity generation by 2020.

Dye coupler

Dye coupler is present in chromogenic film and paper used in photography, primarily color photography. When color developer reduces ionized (exposed) silver-halide crystals, the developer is oxidized, and the oxidized molecules react with dye coupler molecules to form dye in situ. The silver image is removed by subsequent bleach and fix processes, so the final image will consist of the dye image.

Dye coupler technology has seen considerable advancement since the beginning of modern color photography. Major film and paper manufacturers have continually improved the stability of the image dye by improving couplers, particularly since the 1980s, so that archival properties of images are enhanced in newer color papers and films. Generally speaking, dye couplers for paper use are given more emphasis on the image permanence than those for film use, but some modern films (such as Fujichrome Provia films) use variants of couplers that were originally designed for paper use to further improve the image permanence.

Dyeing

Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the objective of achieving color with desired fastness. Dyeing is normally done in a special solution containing dyes and particular chemical material. Dye molecules are fixed to the fibre by absorption, diffusion, or bonding with temperature and time being key controlling factors. The bond between dye molecule and fibre may be strong or weak, depending on the dye used. Dyeing and printing are different applications; in printing color is applied to a localized area with desired patterns and in dyeing it is applied to the entire textile.

The primary source of dye, historically, has been nature, with the dyes being extracted from animals or plants. Since the mid-19th century, however, humans have produced artificial dyes to achieve a broader range of colors and to render the dyes more stable to washing and general use. Different classes of dyes are used for different types of fiber and at different stages of the textile production process, from loose fibers through yarn and cloth to complete garments.

Acrylic fibers are dyed with basic dyes, while nylon and protein fibers such as wool and silk are dyed with acid dyes, and polyester yarn is dyed with disperse dyes. Cotton is dyed with a range of dye types, including vat dyes, and modern synthetic reactive and direct dyes.

Evans Blue (dye)

T-1824 or Evans blue, often incorrectly rendered as Evan's blue, is an azo dye that has a very high affinity for serum albumin. Because of this, it can be useful in physiology in estimating the proportion of body water contained in blood plasma. It fluoresces with excitation peaks at 470 and 540 nm and an emission peak at 680 nm.Evans blue dye has been used as a viability assay on the basis of its penetration into non-viable cells, although the method is subject to error because it assumes that damaged or otherwise altered cells are not capable of repair and therefore are not viable.Evans blue is also used to assess the permeability of the blood–brain barrier to macromolecules. Because serum albumin cannot cross the barrier and virtually all Evans blue is bound to albumin, normally the neural tissue remains unstained. When the blood–brain barrier has been compromised, albumin-bound Evans blue enters the CNS.

Evans blue is pharmacologically active, acting as a negative allosteric modulator of the AMPA and kainate receptors and as an inhibitor of vesicular glutamate transporters. It also acts on P2 receptors.It was named after Herbert McLean Evans, an American anatomist.

Food coloring

Food coloring, or color additive, is any dye, pigment or substance that imparts color when it is added to food or drink. They come in many forms consisting of liquids, powders, gels, and pastes. Food coloring is used both in commercial food production and in domestic cooking. Food colorants are also used in a variety of non-food applications including cosmetics, pharmaceuticals, home craft projects, and medical devices.

Hair coloring

Hair coloring, or hair dyeing, is the practice of changing the hair color. The main reasons for this are cosmetic: to cover gray or white hair, to change to a color regarded as more fashionable or desirable, or to restore the original hair color after it has been discolored by hairdressing processes or sun bleaching.

Hair coloring can be done professionally by a hairdresser or independently at home. Today, hair coloring is very popular, with 75% of women and 18% of men living in Copenhagen having reported using hair dye according to a study by the University of Copenhagen. At-home coloring in the United States reached $1.9 billion in 2011 and is expected to rise to $2.2 billion by 2016.

Henna

Henna (Arabic: حِنَّاء‎) also known as Mehndi (Hindi: मेंहदी) is a dye prepared from the plant Lawsonia inermis, also known as hina, the henna tree, the mignonette tree, and the Egyptian privet, the sole species of the genus Lawsonia.

Henna can also refer to the temporary body art resulting from the staining of the skin from the dyes (see also mehndi). Henna has been used since antiquity to dye skin, hair and fingernails, as well as fabrics including silk, wool and leather. Historically, henna was used in the Arabian Peninsula, Indian Subcontinent, near and Middle East, Carthage, other parts of North Africa and the Horn of Africa. The name is used in other skin and hair dyes, such as black henna and neutral henna, neither of which is derived from the henna plant.

Indigo

Indigo is a deep and rich color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine. It is traditionally regarded as a color in the visible spectrum, as well as one of the seven colors of the rainbow: the color between violet and blue; however, sources differ as to its actual position in the electromagnetic spectrum.

The color indigo is named after the indigo dye derived from the plant Indigofera tinctoria and related species.

The first known recorded use of indigo as a color name in English was in 1289.

Indigo dye

Indigo dye is an organic compound with a distinctive blue color (see indigo). Historically, indigo was a natural dye extracted from the leaves of certain plants, and this process was important economically because blue dyes were once rare. A large percentage of indigo dye produced today, several thousand tonnes each year, is synthetic. It is the blue often associated with denim cloth and blue jeans.

Magenta

Magenta () is a color that is variously defined as purplish-red, reddish-purple, purplish, or mauvish-crimson. In the RGB color model, it is made by mixing equal amounts of blue and red. On color wheels of the RGB (additive) and CMY (subtractive) color models, it is located midway between red and blue. It is the complementary color of green. It is one of the four colors of ink used in color printing by an inkjet printer, along with yellow, black, and cyan, to make all the other colors. The tone of magenta used in printing is called "printer's magenta".

Magenta took its name from an aniline dye made and patented in 1859 by the French chemist François-Emmanuel Verguin, who originally called it fuchsine. It was renamed to celebrate the Italian-French victory at the Battle of Magenta fought between the French and Austrians on June 4, 1859, near the Italian town of Magenta in Lombardy. A virtually identical color, called roseine, was created in 1860 by two British chemists: Chambers Nicolson and George Maule.

The web color magenta is also called fuchsia.

Natural dye

Natural dyes are dyes or colorants derived from plants, invertebrates, or minerals. The majority of natural dyes are vegetable dyes from plant sources—roots, berries, bark, leaves, and wood—and other biological sources such as fungi and lichens.

Archaeologists have found evidence of textile dyeing dating back to the Neolithic period. In China, dyeing with plants, barks and insects has been traced back more than 5,000 years. The essential process of dyeing changed little over time. Typically, the dye material is put in a pot of water and then the textiles to be dyed are added to the pot, which is heated and stirred until the color is transferred. Textile fibre may be dyed before spinning ("dyed in the wool"), but most textiles are "yarn-dyed" or "piece-dyed" after weaving. Many natural dyes require the use of chemicals called mordants to bind the dye to the textile fibres; tannin from oak galls, salt, natural alum, vinegar, and ammonia from stale urine were used by early dyers. Many mordants, and some dyes themselves, produce strong odors, and large-scale dyeworks were often isolated in their own districts.

Throughout history, people have dyed their textiles using common, locally available materials, but scarce dyestuffs that produced brilliant and permanent colors such as the natural invertebrate dyes, Tyrian purple and crimson kermes, became highly prized luxury items in the ancient and medieval world. Plant-based dyes such as woad (Isatis tinctoria), indigo, saffron, and madder were raised commercially and were important trade goods in the economies of Asia and Europe. Across Asia and Africa, patterned fabrics were produced using resist dyeing techniques to control the absorption of color in piece-dyed cloth. Dyes such as cochineal and logwood (Haematoxylum campechianum) were brought to Europe by the Spanish treasure fleets, and the dyestuffs of Europe were carried by colonists to America.

The discovery of man-made synthetic dyes in the mid-19th century triggered a long decline in the large-scale market for natural dyes. Synthetic dyes, which could be produced in large quantities, quickly superseded natural dyes for the commercial textile production enabled by the industrial revolution, and unlike natural dyes, were suitable for the synthetic fibres that followed. Artists of the Arts and Crafts Movement preferred the pure shades and subtle variability of natural dyes, which mellow with age but preserve their true colors, unlike early synthetic dyes, and helped ensure that the old European techniques for dyeing and printing with natural dyestuffs were preserved for use by home and craft dyers. Natural dyeing techniques are also preserved by artisans in traditional cultures around the world.

In the early 21st century, the market for natural dyes in the fashion industry is experiencing a resurgence. Western consumers have become more concerned about the health and environmental impact of synthetic dyes in manufacturing and there is a growing demand for products that use natural dyes. The European Union, for example, has encouraged Indonesian batik cloth producers to switch to natural dyes to improve their export market in Europe.

Purple

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 secondary color made by combining red and blue. The complementary color of purple is yellow.According to surveys in Europe and North America, purple is the color most often associated with rarity, 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. Purple is most favorited color preferences amongst women and girls, and is symbolic of the feminist movement and women's empowerment.

Staining

Staining is an auxiliary technique used in microscopy to enhance contrast in the microscopic image. Stains and dyes are frequently used in biology and medicine to highlight structures in biological tissues for viewing, often with the aid of different microscopes. Stains may be used to define and examine bulk tissues (highlighting, for example, muscle fibers or connective tissue), cell populations (classifying different blood cells, for instance), or organelles within individual cells.

In biochemistry it involves adding a class-specific (DNA, proteins, lipids, carbohydrates) dye to a substrate to qualify or quantify the presence of a specific compound. Staining and fluorescent tagging can serve similar purposes. Biological staining is also used to mark cells in flow cytometry, and to flag proteins or nucleic acids in gel electrophoresis.

Simple staining is staining with only one stain/dye. There are various kinds of multiple staining, many of which are examples of counterstaining, differential staining, or both, including double staining and triple staining.

Staining is not limited to biological materials, it can also be used to study the morphology of other materials for example the lamellar structures of semi-crystalline polymers or the domain structures of block copolymers.

Technicolor

Technicolor is a series of color motion picture processes, the first version dating to 1916, and followed by improved versions over several decades.

It was the second major color process, after Britain's Kinemacolor, and the most widely used color process in Hollywood from 1922 to 1952. Technicolor became known and celebrated for its highly saturated color, and was initially most commonly used for filming musicals such as The Wizard of Oz (1939) and Down Argentine Way (1940), costume pictures such as The Adventures of Robin Hood (1938) and Gone with the Wind (1939), and animated films such as Snow White and the Seven Dwarfs (1937), Gulliver's Travels (1939), and Fantasia (1940). As the technology matured it was also used for less spectacular dramas and comedies. Occasionally, even a film noir—such as Leave Her to Heaven (1945) or Niagara (1953)—was filmed in Technicolor.

"Technicolor" is the trademark for a series of color motion picture processes pioneered by Technicolor Motion Picture Corporation (a subsidiary of Technicolor, Inc.), now a division of the French company Technicolor SA. The Technicolor Motion Picture Corporation was founded in Boston in 1914 (incorporated in Maine in 1915) by Herbert Kalmus, Daniel Frost Comstock, and W. Burton Wescott. The "Tech" in the company's name was inspired by the Massachusetts Institute of Technology, where both Kalmus and Comstock received their undergraduate degrees and were later instructors. Technicolor, Inc. was chartered in Delaware in 1921. Most of Technicolor's early patents were taken out by Comstock and Wescott, while Kalmus served primarily as the company's president and chief executive officer.

Tie-dye

Tie-dye is a modern term invented in the mid-1960s in the United States (but recorded in writing in an earlier form in 1941 as "tied-and-dyed", and 1909 as "tied and dyed" by Charles E. Pellew, referenced below) for a set of ancient resist-dyeing techniques, and for the products of these processes. The process of tie-dye typically consists of folding, twisting, pleating, or crumpling fabric or a garment and binding with string or rubber bands, followed by application of dye(s). The manipulations of the fabric prior to application of dye are called resists, as they partially or completely prevent the applied dye from coloring the fabric. More sophisticated tie-dyes involve additional steps, including an initial application of dye prior to the resist, multiple sequential dye and resist steps, and the use of other types of resists (stitching, stencils) and discharge.

Unlike regular resist-dyeing techniques, tie-dye is characterized by the use of bright, saturated primary colors and bold patterns. These patterns, including the spiral, mandala, and peace sign, and the use of multiple bold colors, have become cliched since the peak popularity of tie-dye in the 1960s and 1970s. The vast majority of currently produced tie-dyes use these designs, and many are mass-produced for wholesale distribution. However, a new interest in more 'sophisticated' tie-dye is emerging in the fashion industry, characterized by simple motifs, monochromatic color schemes, and a focus on fashionable garments and fabrics other than cotton. A few artists continue to pursue tie-dye as an art form rather than a commodity.

Tyrian purple

Tyrian purple (Ancient Greek: πορφύρα, porphúra; Latin: purpura), also known as Tyrian red, Phoenician purple, royal purple, imperial purple or imperial dye, is a reddish-purple natural dye. It is a secretion produced by several species of predatory sea snails in the family Muricidae, rock snails originally known by the name Murex. In ancient times, extracting this dye involved tens of thousands of snails and substantial labor, and as a result, the dye was highly valued. The main chemical is 6,6′-dibromoindigo.

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