A dye is a

color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...

ed substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...

s which do not chemically bind to the material they color. Dye is generally applied in an

aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...

and may require a

mordant A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in ...

to improve the fastness of the dye on the fiber. There are two broad categories of dyes:

natural Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are p ...

and synthetic; Natural dyes are dyes extracted from

plants Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...

Insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of j ...

, or

minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

. The majority of natural dyes are vegetable dyes derived from plant sources such as

roots A root is the part of a plant, generally underground, that anchors the plant body, and absorbs and stores water and nutrients. Root or roots may also refer to: Art, entertainment, and media * ''The Root'' (magazine), an online magazine focusing ...

berries A berry is a small, pulpy, and often edible fruit. Typically, berries are juicy, rounded, brightly colored, sweet, sour or tart, and do not have a stone or pit, although many pips or seeds may be present. Common examples are strawberries, raspb ...

, bark,

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

, and

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...

, as well as other biological sources like

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

. Synthetic dyes are also referred to as "coal tar dyes" because they are derived from substances that, until recently, could only be extracted from coal tar. A synthetic dye consists of a chromophore and an

auxochrome An auxochrome (from Ancient Greek ''auxanō'' "increase" and ''chrōma'' "colour") is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. They themselves fail to produce the colour; but whe ...

added to a

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...

derivative. Both dyes and pigments are colored, because they absorb only some wavelengths of visible

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...

. Dyes are usually soluble in water, whereas pigments are insoluble. Some dyes can be rendered insoluble with the addition of

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

to produce a

lake pigment A lake pigment is a pigment made by precipitating a dye with an inert binder, or mordant, usually a metallic salt. Unlike vermilion, ultramarine, and other pigments made from ground minerals, lake pigments are organic.K. Hunger. W. Herbst "Pigm ...

History

Textile Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not the ...

dyeing dates back to the

Neolithic The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several parts ...

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 Tyrian purple ( grc, πορφύρα ''porphúra''; la, purpura), also known as Phoenician red, Phoenician purple, royal purple, imperial purple, or imperial dye, is a reddish-purple natural dye. The name Tyrian refers to Tyre, Lebanon. It is ...

and crimson kermes were highly prized luxury items in the ancient and medieval world. Plant-based dyes such as

woad ''Isatis tinctoria'', also called woad (), dyer's woad, or glastum, is a flowering plant in the family Brassicaceae (the mustard family) with a documented history of use as a blue dye and medicinal plant. Its genus name, Isatis, derives from ...

indigo Indigo is a deep color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the ancient dye of the same name. The word "indigo" comes from the Latin word ''indicum'', m ...

saffron Saffron () is a spice derived from the flower of ''Crocus sativus'', commonly known as the "saffron crocus". The vivid crimson stigma and styles, called threads, are collected and dried for use mainly as a seasoning and colouring agent i ...

, and

madder ''Rubia'' is the type genus of the Rubiaceae family of flowering plants, which also contains coffee. It contains around 80 species of perennial scrambling or climbing herbs and subshrubs native to the Old World. The genus and its best-known spe ...

were important trade goods in the economies of Asia and Europe. Across Asia and Africa, patterned fabrics were produced using

resist dyeing Resist dyeing (resist-dyeing) is a traditional method of dyeing textiles with patterns. Methods are used to " resist" or prevent the dye from reaching all the cloth, thereby creating a pattern and ground. The most common forms use wax, some typ ...

techniques to control the absorption of color in piece-dyed cloth. Dyes from the

New World The term ''New World'' is often used to mean the majority of Earth's Western Hemisphere, specifically the Americas."America." ''The Oxford Companion to the English Language'' (). McArthur, Tom, ed., 1992. New York: Oxford University Press, p. 3 ...

such as

cochineal The cochineal ( , ; ''Dactylopius coccus'') is a scale insect in the suborder Sternorrhyncha, from which the natural dye carmine is derived. A primarily sessility (motility), sessile parasitism, parasite native to tropical and subtropical Sout ...

and

logwood ''Haematoxylum campechianum'' (blackwood, bloodwood tree, bluewood, campeachy tree, campeachy wood, campeche logwood, campeche wood, Jamaica wood, logwood or logwood tree) is a species of flowering tree in the legume family, Fabaceae, that is na ...

were brought to Europe by the

Spanish Spanish might refer to: * Items from or related to Spain: **Spaniards are a nation and ethnic group indigenous to Spain **Spanish language, spoken in Spain and many Latin American countries **Spanish cuisine Other places * Spanish, Ontario, Can ...

treasure fleets, and the dyestuffs of Europe were carried by colonists to America. Dyed

flax Flax, also known as common flax or linseed, is a flowering plant, ''Linum usitatissimum'', in the family Linaceae. It is cultivated as a food and fiber crop in regions of the world with temperate climates. Textiles made from flax are known in ...

fibers have been found in the

Republic of Georgia A republic () is a "state in which power rests with the people or their representatives; specifically a state without a monarchy" and also a "government, or system of government, of such a state." Previously, especially in the 17th and 18th c ...

in a prehistoric cave dated to 36,000 BP.

Archaeological Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...

evidence shows that, particularly in

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

and

Phoenicia Phoenicia () was an ancient thalassocratic civilization originating in the Levant region of the eastern Mediterranean, primarily located in modern Lebanon. The territory of the Phoenician city-states extended and shrank throughout their histor ...

dyeing Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular ...

has been widely carried out for over 5,000 years. Early dyes were obtained from

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

vegetable Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the flowers, fruits, stems, ...

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

sources, with no to very little processing. By far the greatest source of dyes has been from the

plant kingdom Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...

, notably roots, berries, bark, leaves and wood, only few of which are used on a commercial scale.

Natural and synthetic

The majority of natural dyes are derived from non-animal sources: roots, berries, bark, leaves, wood, fungi and

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.J. Pullar and Sons in Scotland.John Pullar (1803–1878)
- ''The Courier & Advertiser'', 7 June 2016 Other than pigmentation, they have a range of applications including organic dye lasers, optical media (

CD-R CD-R (Compact disc-recordable) is a digital optical disc storage format. A CD-R disc is a compact disc that can be written once and read arbitrarily many times. CD-R discs (CD-Rs) are readable by most CD readers manufactured prior to the in ...

) and

camera sensors An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they refraction, pass through or reflection (physics), reflect off objects) in ...

(

color filter array In digital imaging, a color filter array (CFA), or color filter mosaic (CFM), is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information. The term is also used in reference to e paper devices ...

). The first synthetic dye,

mauve Mauve (, ; , ) is a pale purple color named after the mallow flower (French: ''mauve''). The first use of the word ''mauve'' as a color was in 1796–98 according to the ''Oxford English Dictionary'', but its use seems to have been rare befo ...

, was discovered

serendipitously Serendipity is an unplanned fortunate discovery. Serendipity is a common occurrence throughout the history of product invention and scientific discovery. Etymology The first noted use of "serendipity" was by Horace Walpole on 28 January 1754. I ...

William Henry Perkin Sir William Henry Perkin (12 March 1838 – 14 July 1907) was a British chemist and entrepreneur best known for his serendipitous discovery of the first commercial synthetic organic dye, mauveine, made from aniline. Though he failed in trying ...

in 1856. The discovery of mauveine started a surge in synthetic dyes and in organic chemistry in general. Other

aniline Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine In organic chemistry, an aromatic amine is an organic compound consisting of an aroma ...

dyes followed, such as

fuchsine Fuchsine (sometimes spelled fuchsin) or rosaniline hydrochloride is a magenta dye with chemical formula C20H19N3·HCl.

safranine Safranin (Safranin O or basic red 2) is a biological stain used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring cell nuclei red. This is the classic counterstain in both Gram stains and endos ...

, and

induline Induline is a dye of blue, bluish-red or black shades. Induline consists of a mixture of several intensely colored species, so the name is often indulines. It was one of the first synthetic dyes, discovered in 1863 by J. Dale and Heinrich Caro. Th ...

. Many thousands of synthetic dyes have since been prepared.

Synthetic dyes

The discovery of mauve also led to developments within

immunology Immunology is a branch of medicineImmunology for Medical Students, Roderick Nairn, Matthew Helbert, Mosby, 2007 and biology that covers the medical study of immune systems in humans, animals, plants and sapient species. In such we can see there ...

and

chemotherapy Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemotherap ...

. In 1863 the forerunner to

Bayer AG Bayer AG (, commonly pronounced ; ) is a German multinational pharmaceutical and biotechnology company and one of the largest pharmaceutical companies in the world. Headquartered in Leverkusen, Bayer's areas of business include pharmaceutica ...

was formed in what became

Wuppertal Wuppertal (; "''Wupper Dale''") is, with a population of approximately 355,000, the seventh-largest city in North Rhine-Westphalia as well as the 17th-largest city of Germany. It was founded in 1929 by the merger of the cities and to ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

. In 1891,

Paul Ehrlich Paul Ehrlich (; 14 March 1854 – 20 August 1915) was a Nobel Prize-winning German physician and scientist who worked in the fields of hematology, immunology, and antimicrobial chemotherapy. Among his foremost achievements were finding a cure ...

discovered that certain cells or organisms took up certain dyes selectively. He then reasoned that a sufficiently large dose could be injected to kill pathogenic microorganisms, if the dye did not affect other cells. Ehrlich went on to use a compound to target

syphilis Syphilis () is a sexually transmitted infection caused by the bacterium ''Treponema pallidum'' subspecies ''pallidum''. The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, an ...

, the first time a chemical was used in order to selectively kill bacteria in the body. He also used

methylene blue Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. Methylene blue is a thiazine dye. As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglobin ...

to target the

plasmodium ''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a blood-feeding insect host which then injects parasites into a vert ...

responsible for

malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...

Chemistry

The color of a dye is dependent upon the ability of the substance to absorb light within the visible region of the electromagnetic spectrum (380-750 nm). An earlier theory known as Witt theory stated that a colored dye had two components, a chromophore which imparts color by absorbing light in the visible region (some examples are

nitro Nitro may refer to: Chemistry *Nitrogen, a chemical element and a gas except at very low temperatures, with which many compounds are formed: **Nitro compound, an organic compound containing one or more nitro functional groups, -NO2 **Nitroalkene, ...

, azo,

quinoid In organic chemistry, quinoids are a class of chemical compounds that are derived from quinone. Unlike benzenoid structures, the quinoid part is not aromatic. See also * Benzenoid In organic chemistry, benzenoids are a class of organic compou ...

groups) and an

which serves to deepen the color. This theory has been superseded by modern electronic structure theory which states that the color in dyes is due to excitation of valence π-electrons by visible light.

Types

Dyes are classified according to their solubility and chemical properties.

Acid dye Acid dyes are anionic, soluble in water and are essentially applied from acidic bath. These dyes possess acidic groups, such as SO3H and COOH and are applied on wool, silk and nylon when ionic bond is established between protonated –NH2 group of ...

s are

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...

anionic An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

dyes that are applied to

fiber Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...

s such as

silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the coc ...

wool Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal wool. As ...

nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic. Nylon is a silk-like thermoplastic, generally made from petro ...

and modified

acrylic fiber Acrylic fibers are synthetic fibers made from a polymer (polyacrylonitrile) with an average molecular weight of ~100,000, about 1900 monomer units. For a fiber to be called "acrylic" in the US, the polymer must contain at least 85% acrylonitr ...

s 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 An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

groups in the fiber. Acid dyes are not substantive to

cellulosic Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wa ...

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

dyes that are mainly applied to

s, but find some use for wool and silk. Usually

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...

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 Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distributed ...

. Direct or

substantive dye A substantive dye or direct dye is a dye that adheres to its substrate, typically a textile, by non-ionic forces. Overview The amount of this attraction is known as "substantivity": the higher the substantivity the greater the attraction of th ...

ing is normally carried out in a neutral or slightly

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...

dye bath, at or near

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envir ...

, with the addition of either

sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...

(NaCl) or

sodium sulfate Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 milli ...

(Na₂SO₄) or

sodium carbonate Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...

(Na₂CO₃). Direct dyes are used on

cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor perce ...

, paper,

leather Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hogs, ...

, wool, silk and

. They are also used as

pH indicator A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hence, ...

s and as biological stains.

Mordant dye A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in ...

s require a

, which improves the fastness of the dye against water,

and

perspiration Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distrib ...

. 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 Potassium dichromate, , is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health ...

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 dye Vat dyes are a class of dyes that are classified as such because of the method by which they are applied. Vat dyeing is a process that refers to dyeing that takes place in a bucket or vat. The original vat dye is indigo, once obtained only from p ...

s are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water-soluble

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

of the dye. This form is often colorless, in which case it is referred to as a

Leuco dye A leuco dye (from the Greek λευκός ''leukos'': white ) is a dye which can switch between two chemical forms; one of which is colorless. Reversible transformations can be caused by heat, light or pH; resulting in examples of thermochromism, ...

, and has an affinity for the textile fibre. Subsequent

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

reforms the original insoluble dye. The color of denim is due to

, the original vat dye.

Reactive dyes In a reactive dye, a chromophore (an atom or group whose presence is responsible for the colour of a compound) contains a substituent that chemical reaction, reacts with the substrate. Reactive dyes have good fastness properties owing to the covale ...

utilize a chromophore attached to a

substituent A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and ''functional group'', as well as ''side ...

that is capable of directly reacting with the fiber substrate. The

covalent A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

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

and other

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

fibers at home or in the art studio.

Disperse dye Disperse dye is a category of synthetic dye intended for polyester and related hydrophobic fibers. Disperse dyes are polar molecules containing anthraquinone or azo groups. It is estimated that 85% of disperse dyes are azos or anthraquinone dyes. ...

s were originally developed for the dyeing of

cellulose acetate In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, and ...

, 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 Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...

, but they can also be used to dye nylon, cellulose triacetate, and acrylic fibers. In some cases, a dyeing

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

of 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 Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C-N=N ...

is produced directly onto or within the fiber. This is achieved by treating a fiber with both diazoic and coupling

components Circuit Component may refer to: •Are devices that perform functions when they are connected in a circuit. In engineering, science, and technology Generic systems * System components, an entity with discrete structure, such as an assem ...

. 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 dye Sulfur dyes are the most commonly used dyes manufactured for cotton in terms of volume. They are inexpensive, generally have good colour fastness, wash-fastness, and are easy to apply. Sulfur dyes are predominantly black, brown, and dark blue. Red s ...

s 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 Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. Among the inorganic polysulfides, there are ones which contain anions, which have the general formu ...

. 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. Some dyes commonly used in Staining:

Food dyes

One other class that describes the role of dyes, rather than their mode of use, is the

food dye 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 in both commercial food ...

. Because food dyes are classed as

food additive Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives have been used for centuries as part of an effort to preserve food, for example vinegar (pickling), salt (salt ...

s, 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 Legislation is the process or result of enrolled bill, enrolling, enactment of a bill, enacting, or promulgation, promulgating laws by a legislature, parliament, or analogous Government, governing body. Before an item of legislation becomes law i ...

. Many are azo dyes, although

anthraquinone Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic organic compound with formula . Isomers include various quinone derivatives. The term anthraquinone however refers to the isomer, 9,10-anthraquinone (IUPAC: 9,10-dioxo ...

and

triphenylmethane Triphenylmethane, or triphenyl methane, is the hydrocarbon with the formula (C6H5)3CH. This colorless solid is soluble in nonpolar organic solvents and not in water. Triphenylmethane is the basic skeleton of many synthetic dyes called triarylmetha ...

compounds are used for colors such as

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 Nanometre, nm. In subtractive color systems, used in painting and color printing, it is created by ...

and

blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when obs ...

. 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 dye Laser dyes are dyes used as laser medium in a dye laser. Laser dyes include the coumarins and the rhodamines. Coumarin dyes emit in the green region of the spectrum, whereas rhodamine dyes are used for emission in the yellow-red. The color emi ...

rhodamine 6G Rhodamine 6G is a highly fluorescent rhodamine family dye. It is often used as a tracer dye within water to determine the rate and direction of flow and transport. Rhodamine dyes fluoresce and can thus be detected easily and inexpensively with ...

and

coumarin Coumarin () or 2''H''-chromen-2-one is an aromatic organic chemical compound with formula . Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by a lactone-like chain , forming a second six-membered h ...

dyes. *

Leather Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hogs, ...

dyes, for leather *

Fluorescent brightener Optical brighteners, optical brightening agents (OBAs), fluorescent brightening agents (FBAs), or fluorescent whitening agents (FWAs), are chemical compounds that absorb light in the ultraviolet and violet region (usually 340-370 nm) of the ...

s, for textile fibres and paper *

Solvent dye A solvent dye is a dye soluble in organic solvents. It is usually used as a solution in an organic solvent. Solvent dyes are used to color organic solvents, hydrocarbon fuels, waxes, lubricants, plastics, and other hydrocarbon-based nonpolar mat ...

s, 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. * Mayhems dye, used in water cooling for looks, often rebranded RIT dye

Chromophoric dyes

By the nature of their chromophore, dyes are divided into: * :Acridine dyes, derivates of

acridine Acridine is an organic compound and a nitrogen heterocycle with the formula C13H9N. Acridines are substituted derivatives of the parent ring. It is a planar molecule that is structurally related to anthracene with one of the central CH groups re ...

* :Anthraquinone dyes, derivates of

* Arylmethane dyes ** :Diarylmethane dyes, based on diphenyl methane ** :Triarylmethane dyes, derivates of

* :Azo dyes, based on -N=N- azo structure * Phthalocyanine dyes, derivatives of

phthalocyanine Phthalocyanine () is a large, aromatic, macrocyclic, organic compound with the formula and is of theoretical or specialized interest in chemical dyes and photoelectricity. It is composed of four isoindole units linked by a ring of nitrogen atom ...

* Quinone-imine dyes, derivatives of

quinone The quinones are a class of organic compounds that are formally "derived from aromatic compounds

uch as benzene or naphthalene Uch ( pa, ; ur, ), frequently referred to as Uch Sharīf ( pa, ; ur, ; ''"Noble Uch"''), is a historic city in the southern part of Pakistan's Punjab province. Uch may have been founded as Alexandria on the Indus, a town founded by Alexand ...

by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double ...

** :Azin dyes *** :Eurhodin dyes *** Safranih ***

dyes A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

, derivates of

safranin Safranin (Safranin O or basic red 2) is a biological stain used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring cell nuclei red. This is the classic counterstain in both Gram stains and endospo ...

** Indamins ** :Indophenol dyes, derivates of indophenol ** :Oxazin dyes, derivates of oxazin ** Oxazone dyes, derivates of oxazone ** :Thiazine dyes * :Thiazole dyes * :Safranin dyes * Xanthene dyes ** Fluorene dyes, derivatives of fluorene *** Pyronin dyes ** :Fluorone dyes, based on

fluorone Fluorone is a heterocyclic chemical compound. It forms the core structure for various chemicals, most notably fluorone dyes, including fluorescein, erythrosine and rhodamine. It is an isomer of xanthone Xanthone is an organic compound with t ...

*** :Rhodamine dyes, derivatives of

rhodamine Rhodamine is a family of related dyes, a subset of the triarylmethane dyes. They are derivatives of xanthene. Important members of the rhodamine family are Rhodamine 6G, Rhodamine 123, and Rhodamine B. They are mainly used to dye paper and inks ...

Pollution

Dyes produced by the textile, printing and paper industries are a source of pollution of rivers and waterways. An estimated 700,000 tons of dyestuffs are produced annually (1990 data). The disposal of that material has received much attention, using chemical and biological means.

Classical dyes and their use in medicine and laboratory

According to the

Merriam-Webster Merriam-Webster, Inc. is an American company that publishes reference books and is especially known for its dictionaries. It is the oldest dictionary publisher in the United States. In 1831, George and Charles Merriam founded the company as ...

dictionary, a dye or stain is one that is capable of penetrating living cells or tissues without causing immediate visible degenerative changes; thus, it is also referred to as a vital stain. Supravital staining entails the removal of living cells from an organism, whereas intravital staining entails the injection (or other administration) of the dye into the organism. The term "vital stain" is occasionally used interchangeably with an intravital stain and, in some instances, with a supravital stain, the underlying concept being that the cell being examined is still alive. In a stricter sense, the term "vital staining" means the polar opposite of "supravital staining." If living cells absorb the stain during supravital staining, they exclude it during "vital staining"; for example, they color negatively while only dead cells color positively, and thus viability can be determined by counting the percentage of total cells that stain negatively. Because the dye determines whether the staining is supravital or intravital, a combination of supravital and vital dyes can be used to more accurately classify cells into various groups (e.g., viable, dead, dying) .https://www.intechopen.com/online-first/78967

History

Natural and synthetic

Synthetic dyes

Chemistry

Types

Food dyes

Other important dyes

Chromophoric dyes

Pollution

Classical dyes and their use in medicine and laboratory

See also

References

Further reading