Dye: Difference between revisions

Latest revision as of 02:04, 29 April 2026

File:2019-11-22 Some of the dyes made at De Kat.jpg

A dye is a colored substance that is soluble in some solvent; by contrast pigments are insoluble or nearly so in all solvents. Because of their solubility, dyes can chemically bind to the material they color. Dye is generally applied in an aqueous solution and may require a mordant to improve the fastness of the dye on the fiber.^[1]

The majority of natural dyes are derived from non-animal sources such as roots, berries, bark, leaves, wood, fungi and lichens.^[2] However, due to large-scale demand and technological improvements, most dyes used in the modern world are synthetically produced from substances such as petrochemicals.^[3] Some are extracted from insects and/or minerals.^[4]

Synthetic dyes are produced from various chemicals. The great majority of dyes are obtained in this way because of their superior cost, optical properties (color), and resilience (fastness, mordancy).^[1] Both dyes and pigments are colored, because they absorb only some wavelengths of visible light. Dyes are usually soluble in some solvent, whereas pigments are insoluble. Some dyes can be rendered insoluble with the addition of salt to produce a lake pigment.^[5]^[6]

History

File:Dyeing British Library Royal MS 15.E.iii, f. 269 1482.jpg

Dyeing wool cloth, 1482: from a French translation of Bartolomaeus Anglicus

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,^[7] and the dyestuffs of Europe were carried by colonists to America.^[8]

File:Childhood Joy.jpg

Drying colored cloth

Dyed flax fibers have been found in the Republic of Georgia in a prehistoric cave dated to 36,000 BP.^[9]^[10] 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.^[11]

Early industrialization was conducted by J. Pullar and Sons in Scotland.^[12] The first synthetic dye, mauve, was discovered serendipitously by William Henry Perkin in 1856.^[13]^[14]^[15] 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.^[16]^[17]

The discovery of mauveine in 1856 led to the development of a synthetic dyestuff industry. In Manchester, England, a number of people set up dyestuff manufacturing plant including Ivan Levinstein, Levinstein Ltd,^[18] Charles Dreyfus, Clayton Aniline Company,^[18] William Claus, Claus & co.^[19]

The discovery of mauve also led to developments within immunology and chemotherapy. In 1863 the forerunner to Bayer AG was formed in what became Wuppertal, Germany. In 1891, Paul Ehrlich 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, the first time a chemical was used in order to selectively kill bacteria in the body. He also used methylene blue to target the plasmodium responsible for malaria.^[20]

Classification of dyes

File:Shelve with various hair colours (hair dyes) in a hairdresser shop in Germany (2023).jpg

Shelf with various hair dyes in a hairdresser shop

The color of a dye derives from the absorption of light within the visible region of the electromagnetic spectrum (380–750 nm). The chemical structure determines the light absorption and is therefore the basis for many classification schemes.^[1]

Classification according to chemical structure

Anthraquinone dyes

The basic structure of this group of dyes is anthraquinone. By varying the substituents, almost all colors from yellow to red and from blue to green can be obtained, with red and blue anthraquinone dyes being particularly important. Through reduction, the quinone can be converted into the corresponding water-soluble hydroquinone, allowing anthraquinone dyes to be used as vat dyes. With appropriate substituents, anthraquinone dyes can also be used as disperse dyes for dyeing synthetic fibers. Water-soluble anthraquinone dyes containing sulfonic acid groups are used as acid or reactive dyes.

Azo dyes

File:Azo Group Formula V1.svg

Azo group, R^1,2=aryl / alkenyl

Azo dyes contain an azo group substituted with an aryl group or alkenyl group as their basic structural element. Azo dyes containing multiple azo groups are referred to as bisazo (also disazo), trisazo, tetrakisazo, and polyazo dyes. Aryl substituents are usually benzene or naphthalene derivatives, but may also include heteroaromatic systems such as pyrazoles or pyridones. Enolizable aliphatic groups, for example substituted anilides of acetoacetic acid, are used as alkenyl substituents.

The dyes are synthesized by diazotization of aromatic amines followed by azo coupling of the diazonium salts with electron-rich aromatics or β-dicarbonyl compounds. Azo dyes are by far the most important and extensive class of dyes and are represented in almost all application-related dye categories (→Classification according to application technology). No naturally occurring azo dyes are known. With the exception of turquoise and a brilliant green, almost all colors can be achieved using azo dyes. The azo group is sensitive to reducing agents; it is cleaved, resulting in discoloration of the dye. Some examples of different types of azo dyes (mono- and bisazo dyes / benzene, naphthalene residues / pyridone, acetoacetanilide coupling components / metal complex dyes):

Dioxazine dyes

File:Triphenodioxazine.svg

Triphendioxazine

Dioxazine dyes, also known as triphendioxazine dyes, contain triphendioxazine as their basic structure. These intensely colored, brilliant dyes exhibit good color fastness and thus combine advantages of both azo and anthraquinone dyes. Dioxazine dyes are commercially available as direct and reactive dyes.^[21]

Indigoid dyes

File:Indigo skeletal.svg

Chemical structure of indigo dye, the blue coloration of blue jeans. Although once extracted from plants, indigo dye is now almost exclusively synthesized industrially.^[22]

Indigoid dyes belong to the carbonyl dyes and are used as vat dyes. The most important representative is indigo, which was extracted from plants as a natural dye in ancient times and is still produced industrially in large quantities, particularly for dyeing jeans. Another natural dye is the ancient purple (C.I. Natural Violet 1 / Dibromindigo).

C.I. Vat Blue 1 (Indigo)

C.I. Vat Blue 1 (Indigo)
C.I. Natural Violet 1

C.I. Natural Violet 1
Indirubin

Indirubin

Metal complex dyes

Metal complex dyes consist of complex compounds formed from a metal and one or more dye ligands containing electron donors. Copper and chromium compounds predominate, although cobalt, nickel, and iron complexes are also used to a lesser extent. The ligands are often azo dyes, methine dyes, formazans, or phthalocyanines. Metal complex dyes are characterized by excellent fastness properties.

Formazan dyes

File:Triphenylformazan.svg

Triphenylformazan

Formazan dyes are structurally related to azo dyes. Their basic structure is triphenylformazan. They form chelate complexes with transition metals such as copper, nickel, or cobalt. Depending on the substituents, non-complexed formazans are orange to deep red, whereas metal-complex formazans are violet, blue, or green. They are synthesized by azo coupling of diazonium salts with hydrazones. Of particular commercial importance are blue tetradentate copper chelate complexes of various formazans, which are used mainly as reactive dyes for cotton:

C.I. Reactive Blue 160

C.I. Reactive Blue 160
C.I. Reactive Blue 235

C.I. Reactive Blue 235

Phthalocyanine dyes

Phthalocyanine dyes are copper or nickel metal complexes based on the phthalocyanine structure. They are structurally related to porphyrins and share the annulene element. By introducing water-soluble substituents—primarily via sulfochlorination—turquoise to brilliant green dyes can be obtained. Phthalocyanine dyes are distinguished by outstanding light fastness.

Phthalocyanine (Aza[18]annulene)

Phthalocyanine (Aza[18]annulene)
C.I. Reactive Blue 7

C.I. Reactive Blue 7

Methine dyes

File:Methine Dyes.svg

Structural principle of methine dyes

Methine or polymethine dyes possess conjugated double bonds as their chromophoric system, with two terminal groups acting as an electron acceptor A and an electron donor D. These terminal groups, which usually contain nitrogen or oxygen atoms, may be part of a heterocycle, and the double bonds may be part of an aromatic system. If one or more methine groups are replaced by nitrogen atoms, the dyes are referred to as aza-analog methine dyes. This gives rise to different subclasses:

Cyanine dyes, in which the conjugated double bonds are flanked by a tertiary amino group and a quaternary ammonium compounds. ^[23] If two methine groups are replaced by nitrogen atoms and one terminal group is part of a heterocycle while the other is open-chain, the important diazahemicyanine dyes are formed. Example: Basic Red 22.

Styryl dyes: by insertion of a phenyl ring into the polyene backbone, these dyes contain a styrene structural element. Example: Disperse Yellow 31.

Triarylmethine dyes, also referred to in older literature as triphenylmethane dyes because they are derived from triphenylmethane, in which at least two of the aromatic rings carry electron-donating substituents. Example: Basic Green 4 (malachite green). ^[24]

C.I. Basic Red 22

C.I. Basic Red 22
C.I. Disperse Yellow 31

C.I. Disperse Yellow 31
C.I. Basic Green 4 (malachite green)

C.I. Basic Green 4 (malachite green)

Nitro and nitroso dyes

In nitro dyes, a nitro group is located on an aromatic ring in the ortho position relative to an electron donor, either a hydroxy (–OH) or an amino group (–NH₂). The oldest representative of this dye class is picric acid (2,4,6-trinitrophenol). Hydroxynitro dyes are no longer of commercial importance. This is a relatively small but historically significant dye class, whose representatives are characterized by high light fastness and simple production. Nitro dyes exhibit yellow to brown hues. Owing to their relatively small molecular size, an important application as disperse dyes is the dyeing of polyester fibers. They are also used as acid and pigment dyes.

The rare nitroso dyes are aromatic compounds containing a nitroso group. Nitroso dyes with a hydroxy group in the ortho position to the nitroso group are used exclusively as metal complexes. A typical representative is naphthol green B (C.I. Acid Green 1). ^[25]

Sulfur dyes

Sulfur dyes (sulfin dyes) are water-insoluble, macromolecular dyes that contain disulfide bridges or oligosulfide bonds between aromatic residues. They are produced by melting benzene, naphthalene, or anthracene derivatives with sulfur or polysulfides and have an ill-defined constitution. They are particularly suitable for dyeing cotton fiber. Similar to vat dyes, they are reduced to a water-soluble form (leuco compound) using caustic soda and dithionites or sodium sulfide, applied to the fiber, and then fixed in an insoluble form by oxidation. For toxicological and ecological reasons, oxidation with chromates is increasingly being replaced by low-sulfide sulfur dyes and sulfide-free reducing agents. Owing to their low production costs, sulfur dyes continue to play an important role in terms of volume. They are characterized by good wash and light fastness, although the colors are generally muted.^[26]

Classification according to application technology

While the color shade of a dye is essentially determined by its chromophore, dye properties can be modified by incorporating suitable chemical groups to enable dyeing of different substrates. This leads to a classification of dyes according to the dyeing process. This classification is also used by the Colour Index, an important standard reference in dye chemistry. The Colour Index (C.I.) indicates the dye class, color, and chemical identity. It lists more than 10,000 dyes, over 50% of which are azo dyes.^[27]

Mordant dyes

The term derives from mordant dyeing, in which suitable acid dyes are applied to mordanted fabrics, primarily wool and silk. Prior to dyeing, the fibers are treated with [chromium] , [iron] , or aluminum salts. During subsequent steaming, metal hydroxides form on the fiber. During dyeing, these hydroxides react with the (usually specialized) acid dye to form a metal complex dye. The process on the fiber corresponds to varnishing. ^[28]

When chromium salts are used, the dyes are referred to as chromium dyes. Depending on the dye type, the chromium salt—usually chromates or dichromates—may be added before, during, or after dyeing. Accordingly, pre-mordanting, post-mordanting, and single-bath chromium dyeing processes are distinguished. Chromium dyes are noted for their excellent wet fastness. However, heavy metal contamination of fibers and dyeing wastewater is a significant ecological concern.^[29]

Mordant dyes are designated as "C.I. Mordant Dyes" in the Colour Index. Examples:

C.I. Mordant Black 9

C.I. Mordant Black 9
C.I. Mordant Yellow 8

C.I. Mordant Yellow 8
C.I. Mordant Black 7

C.I. Mordant Black 7
C.I. Mordant Red 60

C.I. Mordant Red 60
C.I. Mordant Blue 9

C.I. Mordant Blue 9

Historically, in addition to chromium, iron, and aluminum salts, mordants based on ammonium vanadate, tannic acid, aluminum oxide, antimony, barium, lead, cobalt, copper, manganese, nickel, tin, and Turkish red oil were also used. Various antimony salts such as potassium antimony tartrate or antimony(III) chloride, as well as sodium silicate and sodium phosphate, and even cow dung, were employed as fixing agents. ^[30]

Direct dyes

Direct dyes (or substantive dyes) are absorbed directly from aqueous solution onto the fiber due to their high substantivity. They are particularly suitable for cellulose fibers. Binding to the fiber occurs through physical interactions, mainly Van der Waals forces. Most direct dyes belong to the azo dye group, especially polyazo dyes. In the Colour Index, they are designated as C.I. Direct Dyes. Examples:

C.I. Direct Blue 8

C.I. Direct Blue 8
C.I. Direct Orange 26

C.I. Direct Orange 26
C.I. Direct Yellow 9

C.I. Direct Yellow 9

Disperse dyes

Disperse dyes, which are almost insoluble in water, are primarily used for dyeing hydrophobic polyester and cellulose acetate. They are finely ground together with dispersing agents, enabling the molecularly dissolved dye to diffuse into the fiber during dyeing, where it forms a solid solution. This results in dyes with good wash and light fastness.

The vast majority of disperse dyes belong to the azo dye class. Disperse dyes represent a highly important group, particularly due to the widespread use and mechanical performance of polyester fibers. In 1999, the total sales volume in Western Europe amounted to 98 million euros.

According to the Colour Index, they are designated as "C.I. Disperse Dyes". Examples:

C.I. Disperse Orange 44

C.I. Disperse Orange 44
C.I. Disperse Blue 797

C.I. Disperse Blue 797
C.I. Disperse Red 177

C.I. Disperse Red 177

Development or coupling dyes

In developing dyes, a practically water-insoluble dye is formed directly on the fiber by the reaction of a water-soluble coupling component (C.I. Azoic Coupling Component) with a water-soluble diazo component (C.I. Azoic Diazo Component). This dye class is mainly used for cellulose fibers and is characterized by very good wet fastness. The most important coupling component in developing dyes is Naphthol AS.

C.I. Azoic Coupling Component 2 (naphthol AS)

C.I. Azoic Coupling Component 2 (naphthol AS)
C.I. Azoic Coupling Component 35 (naphthol AS-LG)

C.I. Azoic Coupling Component 35 (naphthol AS-LG)
C.I. Azoic Diazo Component 3 (Echt scarlet salt GG)

C.I. Azoic Diazo Component 3 (Echt scarlet salt GG)
C.I. Azoic Diazo Component 35 (Variamin blue salt B)

C.I. Azoic Diazo Component 35 (Variamin blue salt B)

Cationic dyes

Cationic dyes are cationic compounds that produce brilliant and lightfast colors, particularly on polyacrylonitrile (PAN) fibers and anionically modified polyester fibers. They form ionic bonds with negatively charged groups on the fiber. Various chromophores can be used in cationic dyes; in methine dyes, the positive charge is delocalized, in contrast to other chromophoric systems.

Although cationic dyes are designated as "C.I. Basic Dyes" in the Colour Index, the term "basic dyes" is no longer commonly used for this dye class in recent literature. ^[25]

C.I. Basic Orange 22

C.I. Basic Orange 22
C.I. Basic Blue 3

C.I. Basic Blue 3
C.I. Basic Blue 54

C.I. Basic Blue 54
C.I. Basic Red 18

C.I. Basic Red 18

Vat dyes

Vat dyes comprise water-insoluble pigments that are converted into their soluble dihydro or leuco base form for dyeing by reduction (vatting) in alkaline solution. The anion exhibits sufficient affinity for cotton or viscose fibers, allowing absorption. The dye is subsequently reconverted to its insoluble form by oxidation, either by atmospheric oxygen or by oxidizing agents. The dye is effectively fixed at the molecular level within the fiber; this "precipitation within the fiber" results in very high wash and light fastness.^[31] Water-insoluble sulfur dyes exhibit similar behavior.

The most important vat dye is indigo. Indanthrene dyes are also of major importance.

Vat dyes are designated as "C.I. Vat Dyes" in the Colour Index. Examples:

C.I. Vat Green 11

C.I. Vat Green 11
C.I. Vat Orange 7

C.I. Vat Orange 7
C.I. Vat Red 23

C.I. Vat Red 23
Flavanthron Yellow

Flavanthron Yellow

Food colorants / food dyes

Food colorants are used as food additives to compensate for color changes caused by processing or to meet consumer expectations. Both naturally occurring and synthetically produced colorants are employed. The use of food colorants is strictly regulated by law—within the EU by Regulation (EC) No. 1333/2008 of December 16, 2008, on food additives.^[32] Only approved additives bearing an E number may be marketed, and these must be declared on the product.^[33]

Food colorants are designated as "C.I. Food Dyes" in the Colour Index.

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.^[34]

Solvent dyes

Solvent dyes, designated as "Solvent Dyes" in the Colour Index, are water-insoluble dyes that are soluble in various organic solvents such as alcohols, esters, or hydrocarbons. As a rule, solvent dye structures do not contain sulfonic acid or carboxyl groups. Exceptions include cationic dyes with an intramolecular sulfonate or carboxylate group acting as the counterion. Solvent dyes occur across various dye classes, including azo dyes, anthraquinone dyes, metal complex dyes, and phthalocyanines. They are used in lacquers (e.g., Zapon dyes for Zapon lacquers), for coloring mineral oil products (Sudan dyes), wax, inks, and transparent plastics. According to the Colour Index, they are designated as C.I. Solvent Dyes.

Examples:

Solvent Yellow 124

Solvent Yellow 124
Solvent Red 27

Solvent Red 27
Solvent Blue 35

Solvent Blue 35
C.I. Solvent Yellow 32

C.I. Solvent Yellow 32
Sudan Black B

Sudan Black B
C.I. Solvent Red 8

C.I. Solvent Red 8

Reactive dyes

During the dyeing process, reactive dyes form a covalent bond with functional groups of the fiber, resulting in dyes with high wet fastness. They constitute the largest group of dyes used for cellulose fibers, but are also employed for wool and polyamide in deep shades.^[35]

Chemically, reactive dyes consist of two components: a chromophore and one or more reactive groups, also referred to as reactive anchors. Two major reactive anchor systems are used:

Heterocyclic compounds, such as halogen-substituted triazines or pyrimidines. During dyeing, these react with hydroxyl groups of the fiber, eliminating halogen hydrides and forming stable covalent ether bonds:

Reaction of reactive dyes with heterocyclic, halogen-containing reactive anchors during the dyeing process

So-called vinylsulfones, which react with nucleophilic groups of the fiber during dyeing via a Michael addition. Here as well, stable ether bonds are formed. In many vinyl sulfone dyes, the vinyl sulfone group is initially present in a protected form as a sulfuric acid semiester. Only under alkaline dyeing conditions is the vinyl sulfone group generated by elimination of sulfuric acid.

Reaction of reactive dyes with vinyl sulfonic reactive anchors during the dyeing process

Both types of reactive anchors may be present simultaneously in a single reactive dye.

Azo dyes are by far the most common chromophores used in reactive dyes. However, other chromophoric systems, such as anthraquinone, formazan, and phthalocyanine dyes, are also important. Reactive dyes are designated as "C.I. Reactive Dyes" in the Colour Index.

Examples:

C.I. Reactive Orange 107

C.I. Reactive Orange 107
C.I. Reactive Blue 2

C.I. Reactive Blue 2
C.I. Reactive Blue 21

C.I. Reactive Blue 21
C.I. Reactive Red 227

C.I. Reactive Red 227
C.I. Reactive Orange 1

C.I. Reactive Orange 1

Acid dyes

Acid dyes are hydrophilic dyes containing anionic substituents, usually sulfonic acid groups. Most acid dyes belong to the azo dye class, although other chromophores also occur. They are mainly used for dyeing wool, silk, and polyamide, with dyeing carried out in the pH range 2–6. When small dye molecules are used, uniform dyeing is achieved, with dye molecules forming primarily salt-like bonds with ammonium groups of the fiber. The wash fastness of such dyes is relatively moderate. With increasing molecular size, dye–fiber binding is enhanced through adsorption forces between the hydrophobic parts of the dye molecule and the fiber. This improves wet fastness, but often at the expense of dyeing uniformity.

Acid dyes are designated as "C.I. Acid Dyes" in the Colour Index. Examples:

C.I. Acid Black 1

C.I. Acid Black 1
C.I. Acid Yellow 36

C.I. Acid Yellow 36
C.I. Acid Blue 117

C.I. Acid Blue 117
Acid Orange 19

Acid Orange 19
C.I. Acid Blue 3 (Patent Blue V)

C.I. Acid Blue 3 (Patent Blue V)

Functional dyes

While conventional dyes are used to modify the appearance of textiles, leather, and paper, functional dyes generally serve non-aesthetic purposes. Typical applications include indicator dyes or voltage-dependent dyes.^[36]

Special dyes can

absorb light at a specific wavelength and convert it into heat (e.g., in chemical and biochemical analysis),^[36]
re-emit absorbed light at a different wavelength (as phosphorescent biomarkers or inks, fluorescence in dye lasers, chemiluminescence in the breaking or formation of chemical bonds in biochemistry),^[36]
change the polarization direction of light (e.g., in frequency doubling or as optical switches),
induce electrical phenomena (e.g., in laser printer applications),
enable photochemical processes.

Laser dyes are used in the production of some lasers, optical media (CD-R), and camera sensors (color filter array).^[37] From an economic perspective, functional dyes are particularly important in the manufacture of CDs and DVDs. The dye molecules are embedded in the polycarbonate of the disc. The laser beam of the burner causes the dye molecules to absorb light energy and convert it into heat, leading to localized melting of the polycarbonate. This slightly altered surface structure is then detected during the reading process.^[38] Laser dyes are for example rhodamine 6G and coumarin dyes.^[39]

Vital dyes

A "vital dye" or stain is a dye capable of penetrating living cells or tissues without causing immediate visible degenerative changes.^[40] Such dyes are useful in medical and pathological fields in order to selectively color certain structures (such as cells) in order to distinguish them from surrounding tissue and thus make them more visible for study (for instance, under a microscope). As the visibility is meant to allow study of the cells or tissues, it is usually important that the dye not have other effects on the structure or function of the tissue that might impair objective observation.

A distinction is drawn between dyes that are meant to be used on cells that have been removed from the organism prior to study (supravital staining) and dyes that are used within a living body - administered by injection or other means (intravital staining) - as the latter is (for instance) subject to higher safety standards, and must typically be a chemical known to avoid causing adverse effects on any biochemistry (until cleared from the tissue), not just to the tissue being studied, or in the short term.

The term "vital stain" is occasionally used interchangeably with both intravital and supravital stains, the underlying concept in either case being that the cells examined are 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).^[41]

Other important dyes

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

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.^[42]
Mayhems dye, used in water cooling for looks, often rebranded RIT dye

Pollution

Dyes produced by the textile, printing and paper industries are a source of pollution of rivers and waterways.^[43] 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.^[44]

Dye degradation and treatment

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Before being released into the environment, the dyes can be broken down into less harmful substances or separated from the water which is then released. There are several ways to do this:

Adsorption

Adsorption is one of the most common and effective methods for dye removal due to its simplicity, low cost, and wide availability of adsorbents. In this process, dye molecules adhere to the surface of solid materials like activated carbon, clay, zeolites, or agricultural waste. The method does not require harsh chemicals or high energy and can achieve high dye removal efficiency. However, its performance depends on the type of dye and the surface properties of the adsorbent and spent adsorbents may also require proper disposal or regeneration.

Membrane filtration

Membrane filtration involve separation of dye molecules from water using semi-permeable membranes. Techniques such as ultrafiltration, nanofiltration, and reverse osmosis can remove dyes based on their size and molecular weight. These methods offer high separation efficiency and can produce reusable water. However, they can be expensive, require high pressure, and are prone to membrane fouling, which reduces their lifespan and performance.

Coagulation and flocculation

This method uses chemical coagulants (alum, ferric chloride) to destabilize and aggregate dye particles into larger flocs. These flocs can then be removed through sedimentation or filtration. Coagulation is commonly used as a pre-treatment step in wastewater treatment plants. While effective for removing particulate-bound dyes, it is less efficient for soluble or highly stable dye compounds and generates a large volume of chemical sludge.

Biological treatment

Biological methods rely on the activity of microorganisms (bacteria, fungi, or algae) to degrade dye molecules. These processes are cost-effective and environmentally friendly, making them attractive for large-scale treatment. However, many synthetic dyes, especially azo dyes, are resistant to microbial breakdown due to their complex structures. Biological methods often require long retention times and are sensitive to operational conditions such as pH, temperature, and the presence of toxic substances.^[45]^[46]

Chemical oxidation

Chemical oxidation uses strong oxidants such as ozone (O
₃), hydrogen peroxide (H
₂O
₂), or chlorine to break down dye molecules into less harmful substances. Advanced oxidation processes (AOPs) generate highly reactive radicals that can fully mineralize organic pollutants. These methods are fast and effective for a wide range of dyes but can be costly and may produce secondary pollutants or require complex equipment.

Photocatalytic degradation

Photocatalytic degradation is a sustainable and advanced method that uses light energy (usually UV or sunlight) in the presence of a semiconductor catalyst like titanium dioxide (TiO
₂) or zinc oxide (ZnO) to degrade dyes. The process generates reactive oxygen species (ROS) such as hydroxyl radicals that break down dye molecules into smaller and less harmful by-products such as water and carbon dioxide. This method is clean, reusable, and effective for treating resistant dyes, making it ideal for modern wastewater treatment strategies. Heterogeneous photocatalysis is one approach to the degradation of dyes.^[47]^[48]

Ion exchange

In ion exchange, dye ions in water are exchanged with non-toxic ions using synthetic resin materials. This method is selective, efficient, and works well for low-concentration dye solutions. It can also be regenerated and reused multiple times. However, its capacity is limited, and it is less effective for removing large, non-ionic, or complex dye molecules.

Electrochemical treatment

Electrochemical treatment uses electric current to drive oxidation or reduction reactions that break down dye molecules. It can be performed without additional chemicals and is capable of complete dye removal. The process is effective for a wide range of dyes and can be automated. However, it requires high energy input, and the equipment can be costly for large-scale operations.

References

↑ ^1.0 ^1.1 ^1.2 Template:Ullmann
↑ Burgess, Rebecca (8 November 2017). Harvesting Color: How to Find Plants and Make Natural Dyes. Artisan Books. ISBN 9781579654252.
↑ Template:Britannica URL
↑ Kassinger, Ruth (2003). Dyes: from sea snails to synthetics. Twenty-First Century Books. ISBN 9780761321125.
↑ Newman, Richard; Gates, Glenn Alan (2020). "The Matter of Madder in the Ancient World". In Svoboda, Marie; Cartwright, Caroline R. (eds.). Mummy Portraits of Roman Egypt: Emerging Research from the APPEAR Project. Los Angeles: J. Paul Getty Museum. Typical later procedures [...] involved mixing the root extracts with a soluble aluminum sulfate salt (such as alum), then adding an alkali [...] to precipitate the lake [...] a dye produces a lake pigment when attached to an inorganic substrate or mordant.
↑ Zollinger, Heinrich (2003). Color Chemistry: Synthesis, Properties, and Applications of Organic Dyes and Pigments (3rd ed.). Wiley-VCH. pp. 224–227. ISBN 9783906390239. Soluble anionic dyes can be converted into insoluble 'lakes' by the addition of alkaline earth or transition metal salts (e.g., Ca2+, Ba2+, Al3+).
↑ Cañamares, M. V.; Leona, M. (15 August 2008). "Study of laccaic acid and other natural anthraquinone dyes by Surface-Enhanced Raman Scattering spectroscopy". In Castillejo, Marta; Moreno, Pablo; Oujja, Mohamed; et al. (eds.). Lasers in the Conservation of Artworks: Proceedings of the International Conference Lacona VII, Madrid, Spain, 17 - 21 September 2007. CRC Press. pp. 29–33. ISBN 9780203882085. Retrieved 8 November 2017 – via Google Books.
↑ Adrosko, Rita J. (8 November 1971). Natural Dyes and Home Dyeing (formerly Titled: Natural Dyes in the United States). Courier Corporation. ISBN 9780486226880. Retrieved 8 November 2017 – via Google Books.
↑ Balter, Michael (11 September 2009). "Clothes Make the (Hu) Man". Science. 325 (5946): 1329. doi:10.1126/science.325_1329a. PMID 19745126.
↑ Kvavadze, Eliso; Bar-Yosef, Ofer; Belfer-Cohen, Anna; Boaretto, Elisabetta; Jakeli, Nino; Matskevich, Zinovi; Meshveliani, Tengiz (11 September 2009). "30,000-Year-Old Wild Flax Fibers". Science. 325 (5946): 1359. Bibcode:2009Sci...325.1359K. doi:10.1126/science.1175404. PMID 19745144.
↑ Liles, J.N (1990). The Art and Craft of Natural Dyeing. University of Tennessee Press. pp. 2–4. ISBN 9780870496707.
↑ "John Pullar (1803–1878)". The Courier & Advertiser. 7 June 2016.
↑ Hübner, Karl (August 2006). "150 Jahre Mauvein". Chemie in unserer Zeit. 40 (4): 274–275. doi:10.1002/ciuz.200690054.
↑ Travis, Anthony S. (1990). "Perkin's Mauve: Ancestor of the Organic Chemical Industry". Technology and Culture. 31 (1): 51–82. doi:10.2307/3105760. JSTOR 3105760.
↑ Eiland, Murray Lee (1999). "Problems Associated with the Dissemination of Synthetic Dyes in the Oriental Carpet Industry". Icon. 5: 138–159. JSTOR 23786082.
↑ Hunger, K., ed. (2003). Industrial Dyes: Chemistry, Properties, Applications. Weinheim: Wiley-VCH. doi:10.1002/3527602011. ISBN 978-3-527-30426-4.^{[page needed]}
↑ Zollinger, H. (2003). Color Chemistry: Synthesis, Properties and Applications of Organic Dyes and Pigments (3rd ed.). Wiley-VCH. ISBN 978-3-906390-23-9.^{[page needed]}
↑ ^18.0 ^18.1 1908 Stock Exchange Year-Book
↑ ICI Dyestuffs Division and predecessor companies archive Claus & Co. Held at University of Manchester Library
↑ Burrows, Andy; Holman, John; Parsons, Andy; Pilling, Gwen; Price, Gareth (2009). Chemistry³: Introducing inorganic, organic and physical chemistry. OUP Oxford. pp. 1005–1006. ISBN 978-0-19-927789-6.
↑ Klaus Hunger, ed. (2003), [[[:Template:Google books]] Industrial Dyes: Chemistry, Properties, Applications] Check |url= value (help), Weinheim: WILEY-VCH Verlag, ISBN 978-3-662-01950-4
↑ Template:Ullmann
↑ Template:RömppOnline
↑ Template:RömppOnline
↑ ^25.0 ^25.1 Heinrich Zollinger (2003), [[[:Template:Google books]] Color Chemistry: Syntheses, Properties, and Applications of Organic Dyes and Pigments] Check |url= value (help) (3. ed.), Weinheim: WILEY-VCH Verlag, ISBN 3-906390-23-3
↑ Template:RömppOnline
↑ Kirk-Othmer, Jacqueline I. Kroschwitz: Encyclopedia of Chemical Technology. 5. Ausgabe, Vol. 9, 2005, ISBN 978-0-471-48494-3, S. 349.
↑ Paul Rys, Heinrich Zollinger: Leitfaden der Farbstoffchemie. 2. Auflage, Verlag Chemie, Weinheim 1976, ISBN 3-527-25650-4, S. 181, 182.
↑ Template:RömppOnline
↑ Jacob Herzfeld (1900), [[[:Template:Google books]] Die Bleichmittel, Beizen und Farbstoffe] Check |url= value (help) (Eigenschaften, Prüfung und praktische Anwendung auf Baumwolle, Wolle, Seide, Halbwolle, Halbseide, Jute, Leinen, etc.) (2 ed.), Unikum Verlag, pp. 55–96
↑ Wittko Francke, Wolfgang Walter: Lehrbuch der Organischen Chemie. S. Hirzel Verlag, Stuttgart 2004, ISBN 3-7776-1221-9, S. 684 f.
↑ Template:EUR-Lex link, retrieved 5 August 2019.
↑ "Zulassung und Verwendung von Lebensmittelzusatzstoffen". Bundesministerium für Ernährung und Landwirtschaft. Retrieved 2019-08-05.
↑ Rodriguez-Amaya, Delia B (February 2016). "Natural food pigments and colorants". Current Opinion in Food Science. 7: 20–26. doi:10.1016/j.cofs.2015.08.004.
↑ H. Zollinger: Chemismus der Reaktivfarbstoffe. In: Angew. Chem. 73, Nr. 4, 1961, S. 125–136, doi:10.1002/ange.19610730402.
↑ ^36.0 ^36.1 ^36.2 John Griffiths: Funktionelle Farbstoffe. Ein neuer Trend in der Farbstoffchemie. In: Chemie in unserer Zeit. 27, Nr. 1, 1993, S. 21–31, doi:10.1002/ciuz.19930270104.
↑ Silfvast, William T. (21 July 2008). Laser Fundamentals. Cambridge University Press. ISBN 9781139855570. Retrieved 8 November 2017 – via Google Books.
↑ Klaus Roth: Die Chemie der schillernden Scheiben: CD, DVD & Co. In: Chemie in unserer Zeit. 41, Nr. 4, 2007, S. 334–345, doi:10.1002/ciuz.200700428.
↑ Duarte, F. J.; Hillman, L. W., eds. (1990). Dye Laser Principles. New York.
↑ "Medical Definition of VITAL DYE". www.merriam-webster.com. Retrieved 2024-10-24.
↑ Ionescu, Sinziana (2023-07-26). "The Use of Indocyanine Green in Colorectal Surgery". Current Topics in Colorectal Surgery. IntechOpen. doi:10.5772/intechopen.100301. ISBN 978-1-83962-335-6.Template:CC-notice
↑ "patentstorm.us". Patentstorm.us. Archived from the original on 12 June 2011. Retrieved 8 November 2017.
↑ Brindley, Lewis (July 2009). "New solution for dye wastewater pollution". Chemistry World. Retrieved 2018-07-08.
↑ Xu, Xiang-Rong; Li, Hua-Bin; Wang, Wen-Hua; Gu, Ji-Dong (2004). "Degradation of dyes in aqueous solutions by the Fenton process". Chemosphere. 57 (7): 595–600. Bibcode:2004Chmsp..57..595X. doi:10.1016/j.chemosphere.2004.07.030. PMID 15488921.
↑ Lin, Jiuyang; Ye, Wenyuan; Xie, Ming; Seo, Dong Han; Luo, Jianquan; Wan, Yinhua; Van der Bruggen, Bart (October 26, 2023). "Environmental impacts and remediation of dye-containing wastewater". Nature Reviews Earth & Environment. 4 (11): 785–803. doi:10.1038/s43017-023-00489-8. ISSN 2662-138X.
↑ Anandita; Raees, Kashif; Shahadat, Mohammad; Ali, Syed Wazed (2023-09-06). "Mechanistic Interaction of Microbe in Dye Degradation and the Role of Inherently Modified Organisms: a Review". Water Conservation Science and Engineering. 8 (1): 43. doi:10.1007/s41101-023-00219-7. ISSN 2364-5687.
↑ Pandit, V.K.; Arbuj, S.S.; Pandit, Y.B.; Naik, S.D.; Rane, S.B.; Mulik, U.P.; Gosavic, S.W.; Kale, B.B. Solar Light driven Dye Degradation using novel Organo–Inorganic (6,13-Pentacenequinone/TiO₂) Nanocomposite". RSC Adv. 2015, 5, 10326-10331.
↑ Khan, Sadia; Noor, Tayyaba; Iqbal, Naseem; Yaqoob, Lubna (2024-05-21). "Photocatalytic Dye Degradation from Textile Wastewater: A Review". ACS Omega. 9 (20): 21751–21767. doi:10.1021/acsomega.4c00887. PMC 11112581 Check |pmc= value (help). PMID 38799325 Check |pmid= value (help).

@@ Line 1: / Line 1: @@
 {{short description|Soluble chemical substance or natural material which can impart color to other materials}}
 {{other uses}}
-[[File:Childhood Joy.jpg|thumb|upright=1.35|Drying colored cloth]]
+[[File:2019-11-22 Some of the dyes made at De Kat.jpg|thumb|right|Dyes made at [[De Kat, Zaandam]]]]A '''dye''' is a [[wiktionary:colored|colored]] substance that is soluble in some solvent; by contrast [[pigment]]s are insoluble or nearly so in all solvents.  Because of their solubility, dyes can chemically bind to the material they color. Dye is generally applied in an [[aqueous solution]] and may require a [[mordant]] to improve the fastness of the dye on the fiber.<ref name="Ullmann's Encyclopedia of Industrial Chemistry">{{Ullmann|last=Booth|first=Gerald|title=Dyes, General Survey |doi=10.1002/14356007.a09_073}}</ref>
-[[File:Indigo skeletal.svg|thumb|Chemical structure of [[indigo dye]], the blue coloration of blue jeans. Although once extracted from plants, indigo dye is now almost exclusively synthesized industrially.<ref name=Ullmann>{{Ullmann|last=Steingruber |first=Elmar|title=Indigo and Indigo Colorants|doi=10.1002/14356007.a14_149.pub2}}</ref>]]
-A '''dye''' is a [[wiktionary:colored|color]]ed substance that chemically bonds to the [[wikt:material|material]] to which it is being applied. This distinguishes dyes from [[pigment]]s which do not chemically bind to the material they color. Dye is generally applied in an [[aqueous solution]] and may require a [[mordant]] to improve the fastness of the dye on the fiber.<ref name="Ullmann's Encyclopedia of Industrial Chemistry">{{Ullmann|last=Booth|first=Gerald|title=Dyes, General Survey |doi=10.1002/14356007.a09_073}}</ref>
+The majority of [[natural dye]]s are derived from non-animal sources such as roots, berries, bark, leaves, wood, fungi and [[lichen]]s.<ref>{{cite book|title=Harvesting Color: How to Find Plants and Make Natural Dyes|first=Rebecca|last=Burgess|date=8 November 2017|publisher=Artisan Books|isbn=9781579654252}}</ref> However, due to large-scale demand and technological improvements, most dyes used in the modern world are synthetically produced from substances such as petrochemicals.<ref>{{Britannica URL |title=Synthetic dyes |url=technology/dye/Synthetic-dyes}}</ref> Some are extracted from [[insect]]s and/or [[mineral]]s.<ref>{{Cite book|last=Kassinger |first=Ruth |title=Dyes: from sea snails to synthetics |date=2003 |publisher=Twenty-First Century Books |isbn=9780761321125}}</ref>
-The majority of [[natural dye]]s are derived from non-animal sources such as roots, berries, bark, leaves, wood, fungi and [[lichen]]s.<ref>{{cite book|url=https://books.google.com/books?id=8CwxW75P_dsC&q=natural+organic+dye+textbook|title=Harvesting Color: How to Find Plants and Make Natural Dyes|first=Rebecca|last=Burgess|date=8 November 2017|publisher=Artisan Books|access-date=8 November 2017|via=Google Books|isbn=9781579654252}}</ref> However, due to large-scale demand and technological improvements, most dyes used in the modern world are synthetically produced from substances such as petrochemicals.<ref>{{Britannica URL |title=Synthetic dyes |url=technology/dye/Synthetic-dyes }}</ref>
+Synthetic dyes are produced from various chemicals. The great majority of dyes are obtained in this way because of their superior cost, optical properties (color), and resilience (fastness, mordancy).<ref name="Ullmann's Encyclopedia of Industrial Chemistry"/> Both dyes and pigments are colored, because they absorb only some wavelengths of visible [[light]]. Dyes are usually soluble in some solvent, whereas pigments are insoluble. Some dyes can be [[Precipitation (chemistry)|rendered insoluble]] with the addition of [[salt (chemistry)|salt]] to produce a [[lake pigment]].<ref>{{Cite book |last1=Newman |first1=Richard |last2=Gates |first2=Glenn Alan |chapter=The Matter of Madder in the Ancient World |title=Mummy Portraits of Roman Egypt: Emerging Research from the APPEAR Project |editor1-first=Marie |editor1-last=Svoboda |editor2-first=Caroline R. |editor2-last=Cartwright |publisher=J. Paul Getty Museum |location=Los Angeles |date=2020 |url=https://www.getty.edu/publications/mummyportraits/part-one/3/ |quote=Typical later procedures [...] involved mixing the root extracts with a soluble aluminum sulfate salt (such as alum), then adding an alkali [...] to precipitate the lake [...] a dye produces a lake pigment when attached to an inorganic substrate or mordant.}}</ref><ref name="Zollinger2003">{{cite book | last = Zollinger | first = Heinrich | title = Color Chemistry: Synthesis, Properties, and Applications of Organic Dyes and Pigments | publisher = Wiley-VCH | year = 2003 | edition = 3rd | pages = 224–227 | isbn = 9783906390239 | quote = Soluble anionic dyes can be converted into insoluble 'lakes' by the addition of alkaline earth or transition metal salts (e.g., Ca2+, Ba2+, Al3+). }}</ref>
-Some are extracted from [[insect]]s and/or [[mineral]]s.<ref>{{Cite book |last=Kassinger |first=Ruth |url=http://archive.org/details/dyesfromseasnail0000kass |title=Dyes : from sea snails to synthetics |date=2003 |location=Brookfield, Conn. |publisher= Twenty-First Century Books |via=Internet Archive |isbn=978-0-7613-2112-5}}</ref>
-Synthetic dyes are produced from various chemicals. The great majority of dyes are obtained in this way because of their superior cost, optical properties (color), and resilience (fastness, mordancy).<ref name="Ullmann's Encyclopedia of Industrial Chemistry"/> Both dyes and pigments are colored, because they absorb only some wavelengths of visible [[light]]. Dyes are usually soluble in some solvent, whereas pigments are insoluble. Some dyes can be [[Precipitation (chemistry)|rendered insoluble]] with the addition of [[salt (chemistry)|salt]] to produce a [[lake pigment]].
 ==History==
@@ Line 16: / Line 12: @@
 [[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 (dye)|kermes]] were highly prized luxury items in the ancient and medieval world. Plant-based dyes such as [[isatis tinctoria|woad]], [[Indigo dye|indigo]], [[Saffron (use)|saffron]], and [[rubia|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 [[Haematoxylum campechianum|logwood]] were brought to Europe by the [[Spain|Spanish]] treasure fleets,<ref>{{cite book|chapter-url=https://books.google.com/books?id=89Qs0uba9VAC&q=dyes+brought+to+europe+from+spain&pg=PA29|title=Lasers in the Conservation of Artworks: Proceedings of the International Conference Lacona VII, Madrid, Spain, 17 - 21 September 2007|editor-first1=Marta|editor-last1=Castillejo|editor-first2=Pablo|editor-last2=Moreno|editor-first3=Mohamed|editor-last3=Oujja|editor-first4=Roxana|editor-last4=Radvan|editor-first5=Javier|editor-last5=Ruiz|display-editors=3|date=15 August 2008|publisher=CRC Press|access-date=8 November 2017|via=Google Books|isbn=9780203882085| chapter=Study of laccaic acid and other natural anthraquinone dyes by Surface-Enhanced Raman Scattering spectroscopy |last1=Cañamares |first1=M. V. |last2=Leona |first2=M. |pages=29–33}}</ref> and the dyestuffs of Europe were carried by colonists to America.<ref>{{cite book|url=https://books.google.com/books?id=EElNckPn0FUC&q=dyestuffs+carried+to+america+by+colonists&pg=PA45|title=Natural Dyes and Home Dyeing (formerly Titled: Natural Dyes in the United States)|first=Rita J.|last=Adrosko|date=8 November 1971|publisher=Courier Corporation|access-date=8 November 2017|via=Google Books|isbn=9780486226880}}</ref>
-Dyed [[flax]] fibers have been found in the [[Georgia (country)|Republic of Georgia]] in a prehistoric cave dated to 36,000 [[Before Present|BP]].<ref>{{cite journal |last1=Balter |first1=Michael |title=Clothes Make the (Hu) Man |journal=Science |date=11 September 2009 |volume=325 |issue=5946 |pages=1329 |doi=10.1126/science.325_1329a |pmid=19745126 }}</ref><ref>{{cite journal |last1=Kvavadze |first1=Eliso |last2=Bar-Yosef |first2=Ofer |last3=Belfer-Cohen |first3=Anna |last4=Boaretto |first4=Elisabetta |last5=Jakeli |first5=Nino |last6=Matskevich |first6=Zinovi |last7=Meshveliani |first7=Tengiz |title=30,000-Year-Old Wild Flax Fibers |journal=Science |date=11 September 2009 |volume=325 |issue=5946 |pages=1359 |doi=10.1126/science.1175404 |pmid=19745144 |bibcode=2009Sci...325.1359K |url=https://nrs.harvard.edu/urn-3:HUL.InstRepos:4270521 |url-access=subscription }}</ref> [[Archaeology|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.<ref>{{Cite book |title=The Art and Craft of Natural Dyeing |last=Liles |first=J.N |publisher=University of Tennessee Press |year=1990 |isbn=9780870496707 |pages=2–4 |url=https://books.google.com/books?id=VUW-l1Wg1wYC|quote= "..By 1500 в.с. the Phoenicians had a thriving Tyrian (royal) purple dye industry in Tyre and other cities. Among the ancients, India was probably the most advanced. The Indians dyed all natural fibers well, especially the more complicated and time-consuming cotton...".}}</ref>
+[[File:Childhood Joy.jpg|thumb|right|Drying colored cloth]]
+Dyed [[flax]] fibers have been found in the [[Georgia (country)|Republic of Georgia]] in a prehistoric cave dated to 36,000 [[Before Present|BP]].<ref>{{cite journal |last1=Balter |first1=Michael |title=Clothes Make the (Hu) Man |journal=Science |date=11 September 2009 |volume=325 |issue=5946 |pages=1329 |doi=10.1126/science.325_1329a |pmid=19745126}}</ref><ref>{{cite journal |last1=Kvavadze |first1=Eliso |last2=Bar-Yosef |first2=Ofer |last3=Belfer-Cohen |first3=Anna |last4=Boaretto |first4=Elisabetta |last5=Jakeli |first5=Nino |last6=Matskevich |first6=Zinovi |last7=Meshveliani |first7=Tengiz |title=30,000-Year-Old Wild Flax Fibers |journal=Science |date=11 September 2009 |volume=325 |issue=5946 |pages=1359 |doi=10.1126/science.1175404 |pmid=19745144 |bibcode=2009Sci...325.1359K |url=https://nrs.harvard.edu/urn-3:HUL.InstRepos:4270521 |url-access=subscription}}</ref> [[Archaeology|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.<ref>{{Cite book |title=The Art and Craft of Natural Dyeing |last=Liles |first=J.N |publisher=University of Tennessee Press |year=1990 |isbn=9780870496707 |pages=2–4 |url=https://books.google.com/books?id=VUW-l1Wg1wYC}}</ref>
+Early industrialization was conducted by [[J. Pullar and Sons]] in Scotland.<ref name=reader>{{cite news |url=https://www.pressreader.com/uk/the-courier-advertiser-fife-edition/20160607/282772060836523 |title=John Pullar (1803–1878) |newspaper=The Courier & Advertiser |date=7 June 2016}}</ref> The first synthetic dye, [[mauveine|mauve]], was discovered [[serendipity|serendipitously]] by [[William Henry Perkin]] in 1856.<ref>{{cite journal |last1=Hübner |first1=Karl |title=150 Jahre Mauvein |journal=Chemie in unserer Zeit |date=August 2006 |volume=40 |issue=4 |pages=274–275 |doi=10.1002/ciuz.200690054}}</ref><ref>{{cite journal |last1=Travis |first1=Anthony S. |title=Perkin's Mauve: Ancestor of the Organic Chemical Industry |journal=Technology and Culture |date=1990 |volume=31 |issue=1 |pages=51–82 |doi=10.2307/3105760 |jstor=3105760}}</ref><ref name="Murray1999">{{cite journal |last1=Eiland |first1=Murray Lee |title=Problems Associated with the Dissemination of Synthetic Dyes in the Oriental Carpet Industry |journal=Icon |date=1999 |volume=5 |pages=138–159 |jstor=23786082}}</ref> 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.<ref>{{cite book |editor-last=Hunger |editor-first=K. |year=2003 |title=Industrial Dyes: Chemistry, Properties, Applications |location=Weinheim |publisher=Wiley-VCH | isbn=978-3-527-30426-4 | doi=10.1002/3527602011}}{{page needed|date=October 2024}}</ref><ref>{{cite book |last=Zollinger |first=H. |year=2003 |title=Color Chemistry: Synthesis, Properties and Applications of Organic Dyes and Pigments |edition=3rd |publisher=Wiley-VCH | isbn=978-3-906390-23-9}}{{page needed|date=October 2024}}</ref>
+The discovery of [[mauveine]] in 1856 led to the development of a synthetic dyestuff industry. In Manchester, England, a number of people set up dyestuff manufacturing plant including [[Ivan Levinstein]], [[Levinstein Ltd]],<ref name="1908 Stock Exchange Year-Book">1908 Stock Exchange Year-Book</ref> [[Charles Dreyfus]], [[Clayton Aniline Company]],<ref name="1908 Stock Exchange Year-Book"/> William Claus, Claus & co.<ref>ICI Dyestuffs Division and predecessor companies archive Claus & Co. Held at University of Manchester Library</ref>
+The discovery of mauve also led to developments within [[immunology]] and [[chemotherapy]]. In 1863 the forerunner to [[Bayer AG]] was formed in what became [[Wuppertal]], [[Germany]]. In 1891, [[Paul Ehrlich]] 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]], the first time a chemical was used in order to selectively kill bacteria in the body. He also used [[methylene blue]] to target the [[plasmodium]] responsible for [[malaria]].<ref>{{cite book |last1=Burrows |first1=Andy |last2=Holman |first2=John |last3=Parsons |first3=Andy |last4=Pilling |first4=Gwen |last5=Price |first5=Gareth |title=Chemistry<sup>3</sup>: Introducing inorganic, organic and physical chemistry |date=2009 |publisher=OUP Oxford |isbn=978-0-19-927789-6 |pages=1005–1006}}</ref>
+== Classification of dyes ==
+[[File:Shelve with various hair colours (hair dyes) in a hairdresser shop in Germany (2023).jpg|thumb|Shelf with various [[hair dyes]] in a hairdresser shop]]
+The color of a dye derives from the absorption of light within the visible region of the electromagnetic spectrum (380–750&nbsp;nm). <!-- who cares about a debunked theory?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 compound|nitro]], [[Azo compound|azo]], [[quinoid]] groups) and an [[auxochrome]] 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-electron]]s by visible light.<ref>{{cite journal |last1=Bafana |first1=Amit |last2=Devi |first2=Sivanesan Saravana |last3=Chakrabarti |first3=Tapan |title=Azo dyes: past, present and the future |journal=Environmental Reviews |date=December 2011 |volume=19 |issue=NA |pages=350–371 |doi=10.1139/a11-018 |bibcode=2011EnvRv..19..350B}}</ref>--> The chemical structure determines the light absorption and is therefore the basis for many classification schemes.<ref name="Ullmann's Encyclopedia of Industrial Chemistry" />
+=== Classification according to chemical structure ===
+==== Anthraquinone dyes ====
+{{Main|Anthraquinone dyes}}The basic structure of this group of dyes is [[anthraquinone]]. By varying the substituents, almost all colors from yellow to red and from blue to green can be obtained, with red and blue anthraquinone dyes being particularly important. Through [[reduction (chemistry)|reduction]], the [[quinone]] can be converted into the corresponding water-soluble [[hydroquinone]], allowing anthraquinone dyes to be used as [[#vat dyes|vat dyes]]. With appropriate substituents, anthraquinone dyes can also be used as [[#disperse dyes|disperse dyes]] for dyeing synthetic fibers. Water-soluble anthraquinone dyes containing sulfonic acid groups are used as [[#acid dyes|acid]] or [[#reactive dyes|reactive dyes]].
+<gallery widths="250">
+Indanthren.svg|[[Indanthrone]]
+Disperse Blue 87.svg|[[Disperse Blue 87]]
+Acid Blue 25 (2).svg|[[Acid Blue 25]]
+Reactive Blue 19.svg|[[Reactive Blue 19]]
+</gallery>
+==== Azo dyes ====
+{{Main|Azo dye}}
+[[File:Azo Group Formula V1.svg|thumb|180px|Azo group, R<sup>1,2</sup>=aryl / alkenyl]]
+Azo dyes contain an [[azo group]] substituted with an [[aryl group]] or [[alkenyl group]] as their basic structural element. Azo dyes containing multiple azo groups are referred to as bisazo (also disazo), trisazo, tetrakisazo, and polyazo dyes. Aryl substituents are usually [[benzene]] or [[naphthalene]] derivatives, but may also include heteroaromatic systems such as [[pyrazole]]s or [[pyridone]]s. Enolizable aliphatic groups, for example substituted [[anilide]]s of [[acetoacetic acid]], are used as alkenyl substituents.
+The dyes are synthesized by diazotization of aromatic amines followed by azo coupling of the diazonium salts with electron-rich aromatics or β-dicarbonyl compounds. Azo dyes are by far the most important and extensive class of dyes and are represented in almost all application-related dye categories (→[[#Classification according to application technology|Classification according to application technology]]). No naturally occurring azo dyes are known. With the exception of [[turquoise (color)|turquoise]] and a brilliant [[green]], almost all colors can be achieved using azo dyes. The azo group is sensitive to [[reducing agent]]s; it is cleaved, resulting in discoloration of the dye. Some examples of different types of azo dyes (mono- and bisazo dyes / benzene, naphthalene residues / pyridone, [[acetoacetanilide]] coupling components / metal complex dyes):
+<gallery widths="250">
+ReactiveBlack5.svg|C.I. [[Reactive Black 5]]
+Disperse Yellow 241.svg|[[Disperse Yellow 241]]
+Mordant Black 9.svg|[[Mordant Black 9]]
+Solvent Yellow 19.svg|[[Solvent Yellow 19]]
+</gallery>
+==== Dioxazine dyes ====
+[[File:Triphenodioxazine.svg|thumb|[[Triphendioxazine]]]]
+Dioxazine dyes, also known as triphendioxazine dyes, contain [[triphendioxazine]] as their basic structure. These intensely colored, brilliant dyes exhibit good [[color fastness]] and thus combine advantages of both azo and anthraquinone dyes. Dioxazine dyes are commercially available as direct and reactive dyes.<ref name="Hunger">{{citation|date=2003 |editor=Klaus Hunger |isbn=978-3-662-01950-4 |location=Weinheim |publisher=WILEY-VCH Verlag |title=Industrial Dyes: Chemistry, Properties, Applications |url={{Google books|uAzS4Hk2TgwC|}}}}<!-- auto-translated from German by Module:CS1 translator --></ref>
+<gallery widths="250">
+Direct Blue 106.svg|[[Direct Blue 106]]
+Reactive Blue 204.svg|[[Reactive Blue 204]]
+</gallery>
+==== Indigoid dyes ====
+{{Main|Indigo}}
+[[File:Indigo skeletal.svg|thumb|Chemical structure of [[indigo dye]], the blue coloration of blue jeans. Although once extracted from plants, indigo dye is now almost exclusively synthesized industrially.<ref name="Ullmann">{{Ullmann|last=Steingruber|first=Elmar|title=Indigo and Indigo Colorants|doi=10.1002/14356007.a14_149.pub2}}</ref>]]
+Indigoid dyes belong to the [[carbonyl dyes]] and are used as vat dyes. The most important representative is indigo, which was extracted from plants as a natural dye in ancient times and is still produced industrially in large quantities, particularly for dyeing [[jeans]]. Another natural dye is the ancient [[purple (dye)|purple]] (''C.I. Natural Violet 1'' / ''Dibromindigo'').
+<gallery widths="250">
+Indigo skeletal.svg|C.I. Vat Blue 1 (Indigo)
+Tyrian-Purple.svg|C.I. Natural Violet 1
+Indirubin.svg|[[Indirubin]]
+</gallery>
+==== Metal complex dyes ====
+Metal complex dyes consist of [[Coordination complex|complex compounds]] formed from a [[metal]] and one or more dye [[ligand]]s containing [[electron donor]]s. Copper and chromium compounds predominate, although cobalt, nickel, and iron complexes are also used to a lesser extent. The ligands are often azo dyes, methine dyes, [[formazan]]s, or [[phthalocyanine]]s. Metal complex dyes are characterized by excellent fastness properties.
+===== Formazan dyes =====
+[[File:Triphenylformazan.svg|thumb|180px|Triphenylformazan]]
+Formazan dyes are structurally related to azo dyes. Their basic structure is [[triphenylformazan]]. They form [[chelate complexes]] with [[transition metal]]s such as [[copper]], [[nickel]], or [[cobalt]]. Depending on the substituents, non-complexed formazans are orange to deep red, whereas metal-complex formazans are violet, blue, or green. They are synthesized by [[azo coupling]] of [[diazonium salts]] with [[hydrazone]]s. Of particular commercial importance are blue tetradentate copper chelate complexes of various formazans, which are used mainly as reactive dyes for cotton:
+<gallery widths="250">
+Reactive Blue 160.svg|C.I. Reactive Blue 160
+Reactive Blue 235.svg|C.I. [[Reactive Blue 235]]
+</gallery>
+===== Phthalocyanine dyes =====
+Phthalocyanine dyes are [[copper]] or [[nickel]] [[metal complexes]] based on the [[phthalocyanine]] structure. They are structurally related to [[porphyrin]]s and share the [[annulene]] element. By introducing water-soluble substituents—primarily via [[sulfochlorination]]—turquoise to brilliant green dyes can be obtained. Phthalocyanine dyes are distinguished by outstanding light fastness.
+<gallery widths="250">
+Phtalocyanine Aza(18)annulene.svg|Phthalocyanine (<span style="color:red">Aza[18]annulene</span>)
+Reactive Blue 7.svg|C.I. Reactive Blue 7
+</gallery>
+==== Methine dyes ====
+{{Main|Polymethine dyes}}
+[[File:Methine Dyes.svg|thumb|360px|Structural principle of methine dyes]]
+Methine or polymethine dyes possess conjugated double bonds as their chromophoric system, with two terminal groups acting as an [[electron acceptor]] '''A''' and an [[electron donor]] '''D'''. These terminal groups, which usually contain nitrogen or oxygen atoms, may be part of a [[heterocycle]], and the double bonds may be part of an aromatic system. If one or more [[methine group]]s are replaced by nitrogen atoms, the dyes are referred to as aza-analog methine dyes. This gives rise to different subclasses:
+''Cyanine dyes'', in which the conjugated double bonds are flanked by a tertiary [[amino group]] and a [[quaternary ammonium compounds]].
+<ref>{{RömppOnline|ID=RD-03-03017|Name=Cyanin-Farbstoffe|Abruf=2019-02-04}}</ref>
+If two methine groups are replaced by nitrogen atoms and one terminal group is part of a heterocycle while the other is open-chain, the important diazahemicyanine dyes are formed. Example: [[Basic Red 22]].
+''Styryl dyes'': by insertion of a phenyl ring into the polyene backbone, these dyes contain a [[styrene]] structural element. Example: [[Disperse Yellow 31]].
+Triarylmethine dyes, also referred to in older literature as [[triphenylmethane dyes]] because they are derived from [[triphenylmethane]], in which at least two of the aromatic rings carry electron-donating substituents. Example: [[Basic Green 4]] (malachite green).
+<ref>{{RömppOnline|ID=RD-20-02667|Name=Triarylmethan-Farbstoffe|Abruf=2019-01-14}}</ref>
+<gallery widths="250">
+Basic Red 22.svg|C.I. Basic Red 22
+Disperse Yellow 31.svg|C.I. Disperse Yellow 31
+Malachite green Structural Formulae V.1.svg|C.I. Basic Green 4 (malachite green)
+</gallery>
+==== Nitro and nitroso dyes ====
+In nitro dyes, a [[nitro group]] is located on an aromatic ring in the ortho position relative to an electron donor, either a hydroxy (–OH) or an amino group (–NH<sub>2</sub>). The oldest representative of this dye class is [[picric acid]] (2,4,6-trinitrophenol). Hydroxynitro dyes are no longer of commercial importance. This is a relatively small but historically significant dye class, whose representatives are characterized by high light fastness and simple production. Nitro dyes exhibit yellow to brown hues. Owing to their relatively small molecular size, an important application as disperse dyes is the dyeing of polyester fibers. They are also used as acid and pigment dyes.
+The rare nitroso dyes are aromatic compounds containing a nitroso group. Nitroso dyes with a hydroxy group in the ortho position to the nitroso group are used exclusively as metal complexes. A typical representative is naphthol green B (C.I. Acid Green 1).
+<ref name="Zollinger">{{citation|author=Heinrich Zollinger |date=2003 |edition=3. |isbn=3-906390-23-3 |location=Weinheim |publisher=WILEY-VCH Verlag |title=Color Chemistry: Syntheses, Properties, and Applications of Organic Dyes and Pigments |url={{Google books|0Ynge4E5rqYC|}}}}<!-- auto-translated from German by Module:CS1 translator --></ref>
+<gallery widths="250">
+Pikrinsäure.svg|Picric acid
+C.I. Acid Orange 3.svg|[[Acid Orange 3]]
+Disperse Yellow 42.svg|[[Disperse Yellow 42]]
+Naphthol Green B.svg|C.I. Acid Green 1
+</gallery>
+==== Sulfur dyes ====
+Sulfur dyes (sulfin dyes) are water-insoluble, macromolecular dyes that contain disulfide bridges or oligosulfide bonds between aromatic residues. They are produced by melting [[benzene]], [[naphthalene]], or [[anthracene]] [[derivatives (chemistry)|derivatives]] with [[sulfur]] or [[polysulfide]]s and have an ill-defined [[constitution]]. They are particularly suitable for dyeing [[cotton fiber]]. Similar to vat dyes, they are reduced to a water-soluble form ([[leuco compound]]) using [[caustic soda]] and [[dithionite]]s or [[sodium sulfide]], applied to the fiber, and then fixed in an insoluble form by [[oxidation]]. For toxicological and ecological reasons, oxidation with [[chromates]] is increasingly being replaced by low-sulfide sulfur dyes and sulfide-free reducing agents. Owing to their low production costs, sulfur dyes continue to play an important role in terms of volume. They are characterized by good wash and light fastness, although the colors are generally muted.<ref>{{RömppOnline|ID=RD-19-01378|Name=Schwefel-Farbstoffe|Abruf=2019-01-14}}</ref>
+=== Classification according to application technology ===
+While the color shade of a dye is essentially determined by its chromophore, dye properties can be modified by incorporating suitable chemical groups to enable dyeing of different substrates. This leads to a classification of dyes according to the dyeing process. This classification is also used by the [[Colour Index]], an important standard reference in dye chemistry. The Colour Index (C.I.) indicates the dye class, color, and chemical identity. It lists more than 10,000 dyes, over 50% of which are azo dyes.<ref name="KirkOthmer">Kirk-Othmer, Jacqueline I. Kroschwitz: ''Encyclopedia of Chemical Technology.'' 5. Ausgabe, Vol. 9, 2005, ISBN 978-0-471-48494-3, S.&nbsp;349.</ref>
+==== Mordant dyes ====
+The term derives from [[mordant dye]]ing, in which suitable acid dyes are applied to ''mordanted'' fabrics, primarily wool and silk. Prior to dyeing, the fibers are treated with [chromium]
+, [iron]
+, or [[aluminum]] salts. During subsequent steaming, metal hydroxides form on the fiber. During dyeing, these [[hydroxide]]s react with the (usually specialized) acid dye to form a [[#metal complex dyes|metal complex dye]]. The process on the fiber corresponds to [[varnishing#mordant dyes|varnishing]].
+<ref>[[Paul Rys]], Heinrich Zollinger: ''Leitfaden der Farbstoffchemie.'' 2. Auflage, Verlag Chemie, Weinheim 1976, ISBN 3-527-25650-4, S.&nbsp;181, 182.</ref>
+When chromium salts are used, the dyes are referred to as chromium dyes. Depending on the dye type, the chromium salt—usually [[chromates]] or dichromates—may be added before, during, or after dyeing. Accordingly, pre-mordanting, post-mordanting, and single-bath chromium dyeing processes are distinguished. Chromium dyes are noted for their excellent wet fastness. However, heavy metal contamination of fibers and dyeing wastewater is a significant ecological concern.<ref>{{RömppOnline|ID=RD-03-01712|Name=Chromierungsfarbstoffe|Abruf=2019-01-23}}</ref>
+Mordant dyes are designated as "C.I. Mordant Dyes" in the Colour Index. Examples:
+<gallery widths="250">
+Mordant Black 9.svg|C.I. Mordant Black 9
+Mordant Yellow 8.svg|C.I. Mordant Yellow 8
+Mordant Black 7.svg|C.I. Mordant Black 7
+Mordant Red 60.svg|C.I. Mordant Red 60
+Mordant Blue 9.svg|C.I. Mordant Blue 9
+</gallery>
+Historically, in addition to chromium, iron, and aluminum salts, mordants based on [[ammonium vanadate]], [[tannic acid]], [[aluminum oxide]], [[antimony]], [[barium]], [[lead]], [[cobalt]], [[copper]], [[manganese]], [[nickel]], [[tin]], and [[Turkish red oil]] were also used. Various antimony salts such as [[potassium antimony tartrate]] or [[antimony(III) chloride]], as well as [[sodium silicate]] and [[sodium phosphate]], and even [[cow dung]], were employed as fixing agents.
+<ref name="JHerzfeld">{{citation|author=Jacob Herzfeld |date=1900 |edition=2 |pages=55–96 |publisher=Unikum Verlag |title=Die Bleichmittel, Beizen und Farbstoffe |type=Eigenschaften, Prüfung und praktische Anwendung auf Baumwolle, Wolle, Seide, Halbwolle, Halbseide, Jute, Leinen, etc. |url={{Google books|YxjiBQAAQBAJ||page=55}}}}<!-- auto-translated from German by Module:CS1 translator --></ref>
+==== Direct dyes ====
+{{Main|Substantive dye}}
+Direct dyes (or [[substantive dye]]s) are absorbed directly from aqueous solution onto the fiber due to their high [[substantivity (textile chemistry)|substantivity]]. They are particularly suitable for [[cellulose]] fibers. Binding to the fiber occurs through physical interactions, mainly [[Van der Waals force]]s. Most direct dyes belong to the azo dye group, especially polyazo dyes. In the Colour Index, they are designated as ''C.I. Direct Dyes''. Examples:
+<gallery widths="250">
+Direct Blue 8 (free acid).svg|C.I. Direct Blue 8
+Direct Orange 26 (free acid).svg|C.I. Direct Orange 26
+Direct Yellow 9 (free acid).svg|C.I. Direct Yellow 9
+</gallery>
+==== Disperse dyes ====
+Disperse dyes, which are almost insoluble in water, are primarily used for dyeing hydrophobic polyester and [[cellulose acetate]]. They are finely ground together with [[dispersing agents]], enabling the molecularly dissolved dye to diffuse into the fiber during dyeing, where it forms a solid solution. This results in dyes with good wash and light fastness.
+The vast majority of disperse dyes belong to the azo dye class. Disperse dyes represent a highly important group, particularly due to the widespread use and mechanical performance of polyester fibers. In 1999, the total sales volume in Western Europe amounted to 98 million euros.
+According to the Colour Index, they are designated as "C.I. Disperse Dyes". Examples:
+<gallery widths="250">
+Disperse Orange 44.svg|C.I. Disperse Orange 44
+Disperse Blue 79.svg|C.I. Disperse Blue 797
+Disperse Red 177.svg|C.I. Disperse Red 177
+</gallery>
+==== Development or coupling dyes ====
+In developing dyes, a practically water-insoluble dye is formed directly on the fiber by the reaction of a water-soluble coupling component (''C.I. Azoic Coupling Component'') with a water-soluble diazo component (''C.I. Azoic Diazo Component''). This dye class is mainly used for cellulose fibers and is characterized by very good wet fastness. The most important coupling component in developing dyes is [[Naphthol AS]].
+<gallery widths="250">
+Azoic Coupling Component 2.svg|C.I. Azoic Coupling Component 2 (naphthol AS)
+Azoic Coupling Component 35.svg|C.I. Azoic Coupling Component 35 (naphthol AS-LG)
+Azoic Diazo Component 3.svg|C.I. Azoic Diazo Component 3 (Echt scarlet salt GG)
+Azoic Diazo Component 35.svg|C.I. Azoic Diazo Component 35 (Variamin blue salt B)
+</gallery>
+==== Cationic dyes ====
+Cationic dyes are [[cation]]ic compounds that produce brilliant and lightfast colors, particularly on [[polyacrylonitrile]] (PAN) fibers and anionically modified [[polyester]] fibers. They form ionic bonds with negatively charged groups on the fiber. Various chromophores can be used in cationic dyes; in methine dyes, the positive charge is delocalized, in contrast to other chromophoric systems.
+Although cationic dyes are designated as "C.I. Basic Dyes" in the Colour Index, the term "basic dyes" is no longer commonly used for this dye class in recent literature.
+<ref name="Zollinger"/>
+<gallery widths="250">
+Basic Orange 22.svg|C.I. Basic Orange 22
+Basic Blue 3.svg|C.I. Basic Blue 3
+Basic Blue 54.svg|C.I. Basic Blue 54
+Basic Red 18.svg|C.I. Basic Red 18
+</gallery>
+==== Vat dyes ====
+Vat dyes comprise water-insoluble pigments that are converted into their soluble dihydro or [[leuco base]] form for dyeing by [[reduction (chemistry)|reduction]] (''vatting'') in alkaline solution. The anion exhibits sufficient affinity for cotton or viscose fibers, allowing absorption. The dye is subsequently reconverted to its insoluble form by oxidation, either by atmospheric oxygen or by oxidizing agents. The dye is effectively fixed at the molecular level within the fiber; this "precipitation within the fiber" results in very high wash and light fastness.<ref>Wittko Francke, Wolfgang Walter: ''Lehrbuch der Organischen Chemie.'' S. Hirzel Verlag, Stuttgart 2004, ISBN 3-7776-1221-9, S.&nbsp;684&nbsp;f.</ref> Water-insoluble [[#sulfur dyes|sulfur dyes]] exhibit similar behavior.
+The most important vat dye is [[#Indigoide dyes|indigo]]. [[Indanthrene]] dyes are also of major importance.
+Vat dyes are designated as "C.I. Vat Dyes" in the Colour Index. Examples:
+<gallery widths="250">
+Vat Green 11.svg|C.I. Vat Green 11
+Vat Orange 7.svg|C.I. Vat Orange 7
+Vat Red 23.svg|C.I. Vat Red 23
+Flavanthron.svg|[[Flavanthron Yellow]]
+</gallery>
+==== Food colorants / food dyes ====
+{{Main|Food coloring}}
+Food colorants are used as [[food additive]]s to compensate for color changes caused by processing or to meet consumer expectations. Both naturally occurring and synthetically produced colorants are employed. The use of food colorants is strictly regulated by law—within the [[EU]] by Regulation (EC) No. 1333/2008 of December 16, 2008, on food additives.<ref>{{EUR-Lex link|uri=uriserv:OJ.L_.2008.354.01.0016.01.DEU|title=Verordnung (EG) Nr. 1333/2008 16 December 2008 über Lebensmittelzusatzstoffe|format=PDF}}, retrieved 5 August 2019.</ref> Only approved additives bearing an E number may be marketed, and these must be declared on the product.<ref>{{cite web|access-date=2019-08-05 |publisher=Bundesministerium für Ernährung und Landwirtschaft |title=Zulassung und Verwendung von Lebensmittelzusatzstoffen |url=https://www.bmel.de/DE/Ernaehrung/SichereLebensmittel/SpezielleLebensmittelUndZusaetze/Zusatzstoffe/_Texte/Lebensmittelzusatzstoffe.html}}<!-- auto-translated from German by Module:CS1 translator --></ref>
+Food colorants are designated as "C.I. Food Dyes" in the Colour Index.
+Because food dyes are classed as [[food additive]]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 [[law|legislation]]. Many are [[Azo compound|azo]] dyes, although [[anthraquinone]] and [[triphenylmethane]] compounds are used for colors such as [[green]] and [[blue]]. Some naturally occurring dyes are also used.<ref>{{cite journal |last1=Rodriguez-Amaya |first1=Delia B |date=February 2016 |title=Natural food pigments and colorants |journal=Current Opinion in Food Science |volume=7 |pages=20–26 |doi=10.1016/j.cofs.2015.08.004}}</ref>
+==== Solvent dyes ====
+Solvent dyes, designated as "Solvent Dyes" in the Colour Index, are water-insoluble dyes that are soluble in various organic solvents such as alcohols, esters, or hydrocarbons. As a rule, solvent dye structures do not contain sulfonic acid or carboxyl groups. Exceptions include cationic dyes with an intramolecular sulfonate or carboxylate group acting as the counterion. Solvent dyes occur across various dye classes, including azo dyes, anthraquinone dyes, metal complex dyes, and phthalocyanines. They are used in lacquers (e.g., [[Zapon dyes]] for [[Zapon lacquers]]), for coloring mineral oil products ([[Sudan dyes]]), [[wax]], [[ink]]s, and transparent plastics. According to the Colour Index, they are designated as ''C.I. Solvent Dyes''.
+Examples:
+<gallery widths="250">
+Solvent Yellow 124.svg|[[Solvent Yellow 124]]
+Oil Red O.svg|[[Solvent Red 27]]
+Oil Blue 35 Structural Formula V1.svg|[[Solvent Blue 35]]
+Solvent Yellow 32.svg|C.I. Solvent Yellow 32
+Sudan Black B.svg|[[Sudan Black B]]
+Solvent Red 8.svg|C.I. Solvent Red 8
+</gallery>
+==== Reactive dyes ====
+{{Main|Reactive dye}}
+During the dyeing process, reactive dyes form a [[covalent bond]] with functional groups of the fiber, resulting in dyes with high wet fastness. They constitute the largest group of dyes used for cellulose fibers, but are also employed for wool and polyamide in deep shades.<ref>H. Zollinger: ''Chemismus der Reaktivfarbstoffe''. In: ''[[Angewandte Chemie (Zeitschrift)|Angew. Chem.]]'' 73, Nr. 4, 1961, S.&nbsp;125–136, [[doi:10.1002/ange.19610730402]].</ref>
-Early industrialization was conducted by [[J. Pullar and Sons]] in Scotland.<ref name=reader>{{cite news |url=https://www.pressreader.com/uk/the-courier-advertiser-fife-edition/20160607/282772060836523 |title=John Pullar (1803–1878) |newspaper=The Courier & Advertiser |date=7 June 2016}}</ref> The first synthetic dye, [[mauveine|mauve]], was discovered [[serendipity|serendipitously]] by [[William Henry Perkin]] in 1856.<ref>{{cite journal |last1=Hübner |first1=Karl |title=150 Jahre Mauvein |journal=Chemie in unserer Zeit |date=August 2006 |volume=40 |issue=4 |pages=274–275 |doi=10.1002/ciuz.200690054 }}</ref><ref>{{cite journal |last1=Travis |first1=Anthony S. |title=Perkin's Mauve: Ancestor of the Organic Chemical Industry |journal=Technology and Culture |date=1990 |volume=31 |issue=1 |pages=51–82 |doi=10.2307/3105760 |jstor=3105760 }}</ref><ref name="Murray1999">{{cite journal |last1=Eiland |first1=Murray Lee |title=Problems Associated with the Dissemination of Synthetic Dyes in the Oriental Carpet Industry |journal=Icon |date=1999 |volume=5 |pages=138–159 |jstor=23786082 }}</ref> 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.<ref>{{cite book |editor-last=Hunger |editor-first=K. |year=2003 |title=Industrial Dyes: Chemistry, Properties, Applications |location=Weinheim |publisher=Wiley-VCH | isbn=978-3-527-30426-4 | doi=10.1002/3527602011}}{{pn|date=October 2024}}</ref><ref>{{cite book |last=Zollinger |first=H. |year=2003 |title=Color Chemistry: Synthesis, Properties and Applications of Organic Dyes and Pigments |edition=3rd |location=Weinheim |publisher=Wiley-VCH | isbn=978-3-906390-23-9}}{{pn|date=October 2024}}</ref>
+Chemically, reactive dyes consist of two components: a chromophore and one or more reactive groups, also referred to as reactive anchors. Two major reactive anchor systems are used:
-The discovery of [[mauveine]] in 1856 led to the development of a synthetic dyestuff industry. In Manchester, England, a number of people set up dyestuff manufacturing plant including [[Ivan Levinstein]], [[Levinstein Ltd]],<ref>1908 Stock Exchange Year-Book </ref> [[Charles Dreyfus]], [[Clayton Aniline Company]],<ref>1908 Stock Exchange Year-Book</ref> William Claus, Claus & co.<ref>ICI Dyestuffs Division and predecessor companies archive Claus & Co. Held at University of Manchester Library</ref>
+* Heterocyclic compounds, such as halogen-substituted [[triazine]]s or [[pyrimidine]]s. During dyeing, these react with hydroxyl groups of the fiber, eliminating [[halogen hydrides]] and forming stable covalent [[ether]] bonds:
-The discovery of mauve also led to developments within [[immunology]] and [[chemotherapy]]. In 1863 the forerunner to [[Bayer AG]] was formed in what became [[Wuppertal]], [[Germany]]. In 1891, [[Paul Ehrlich]] 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]], the first time a chemical was used in order to selectively kill bacteria in the body. He also used [[methylene blue]] to target the [[plasmodium]] responsible for [[malaria]].<ref>{{cite book |last1=Burrows |first1=Andy |last2=Holman |first2=John |last3=Parsons |first3=Andy |last4=Pilling |first4=Gwen |last5=Price |first5=Gareth |title=Chemistry³: Introducing inorganic, organic and physical chemistry |date=2009 |publisher=OUP Oxford |isbn=978-0-19-927789-6 |pages=1005–1006 }}</ref>
+[[File:Heterocyclic Reactive Groups - Reaction.svg|frameless|Reaction of reactive dyes with heterocyclic, halogen-containing reactive anchors during the dyeing process|357x357px]]
-[[File:Blick in Farbstoffsammlung 01.JPG|thumb|Historical collection of over 10,000 dyes at [[Technical University Dresden]], [[Germany]]]]
+* So-called [[Vinyl sulfone|vinylsulfones]], which react with [[nucleophilic]] groups of the fiber during dyeing via a [[Michael addition]]. Here as well, stable ether bonds are formed. In many vinyl sulfone dyes, the vinyl sulfone group is initially present in a protected form as a sulfuric acid semiester. Only under alkaline dyeing conditions is the vinyl sulfone group generated by elimination of sulfuric acid.
-== Chemistry ==
+[[File:VSReactiveGroups Reaction.svg|frameless|Reaction of reactive dyes with vinyl sulfonic reactive anchors during the dyeing process|451x451px]]
-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&nbsp;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 compound|nitro]], [[Azo compound|azo]], [[quinoid]] groups) and an [[auxochrome]] 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-electron]]s by visible light.<ref>{{cite journal |last1=Bafana |first1=Amit |last2=Devi |first2=Sivanesan Saravana |last3=Chakrabarti |first3=Tapan |title=Azo dyes: past, present and the future |journal=Environmental Reviews |date=December 2011 |volume=19 |issue=NA |pages=350–371 |doi=10.1139/a11-018 |bibcode=2011EnvRv..19..350B }}</ref>
-==Types==
+Both types of reactive anchors may be present simultaneously in a single reactive dye.
-[[File:RITdye.JPG|thumb|RIT brand dye from mid-20th century Mexico, part of the permanent collection of the [[Museo del Objeto del Objeto]]]]
-[[File:Hårfärgning - 2007.jpg|thumb|A [[woman]] dyeing her [[hair]]]]
-Dyes are classified according to their solubility and chemical properties.<ref name="Ullmann's Encyclopedia of Industrial Chemistry"/>
-'''[[Acid dye]]s''' are [[water]]-[[soluble]] [[anionic]] dyes that are applied to [[fiber]]s such as [[silk]], [[wool]], [[nylon]] and modified [[acrylic fiber]]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]] groups in the fiber. Acid dyes are not substantive to [[Cellulose|cellulosic]] fibers. Most synthetic food colors fall in this category. Examples of acid dye are Alizarine Pure Blue B, [[Acid red 88]], etc.
+Azo dyes are by far the most common chromophores used in reactive dyes. However, other chromophoric systems, such as anthraquinone, formazan, and phthalocyanine dyes, are also important. Reactive dyes are designated as "C.I. Reactive Dyes" in the Colour Index.
-'''Basic dyes''' are water-soluble [[cationic]] dyes that are mainly applied to [[acrylic fiber]]s, 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]].
+Examples:
+<gallery widths="250">
+Reactive Orange 107.svg|C.I. [[Reactive Orange 107]]
+Cibacron Blue F 3GA.svg|C.I. [[Reactive Blue 2]]
+Reactive Blue 21.svg|C.I. Reactive Blue 21
+Reactive Red 227.svg|C.I. Reactive Red 227
+Procionbrilliantorange GS.svg|C.I. Reactive Orange 1
+</gallery>
-'''Direct''' or '''[[substantive dye]]ing''' 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]] (Na<sub>2</sub>SO<sub>4</sub>) or [[sodium carbonate]] (Na<sub>2</sub>CO<sub>3</sub>). Direct dyes are used on [[cotton]], paper, [[leather]], wool, silk and [[nylon]]. They are also used as [[pH indicator]]s and as [[staining (biology)|biological stains]].
+==== Acid dyes ====
+{{Main|Acid dye}}
-[[organic dye laser|Laser dyes]] are used in the production of some lasers, optical media ([[CD-R#ORGANIC DYE|CD-R]]), and [[camera sensors]] ([[color filter array]]).<ref>{{cite book|url=https://books.google.com/books?id=_F4hAwAAQBAJ&q=organic+dye+laser&pg=PA539|title=Laser Fundamentals|first=William T.|last=Silfvast|date=21 July 2008|publisher=Cambridge University Press|access-date=8 November 2017|via=Google Books|isbn=9781139855570}}</ref>
+Acid dyes are [[Hydrophile|hydrophilic]] dyes containing [[anion]]ic substituents, usually sulfonic acid groups. Most acid dyes belong to the azo dye class, although other chromophores also occur. They are mainly used for dyeing wool, silk, and polyamide, with dyeing carried out in the pH range 2–6. When small dye molecules are used, uniform dyeing is achieved, with dye molecules forming primarily salt-like bonds with ammonium groups of the fiber. The wash fastness of such dyes is relatively moderate. With increasing molecular size, dye–fiber binding is enhanced through adsorption forces between the hydrophobic parts of the dye molecule and the fiber. This improves wet fastness, but often at the expense of dyeing uniformity.
-'''[[Mordant dye]]s''' 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.
+Acid dyes are designated as "C.I. Acid Dyes" in the Colour Index. Examples:
+<gallery widths="250">
+Acid Black 1.svg|C.I. Acid Black 1
+Acid Yellow 36.svg|C.I. Acid Yellow 36
+Acid Blue 117.svg|C.I. Acid Blue 117
+Acid Orange 19.svg|[[Acid Orange 19]]
+Patent blue V.svg|C.I. Acid Blue 3 ([[Patent Blue V]])
+</gallery>
-'''[[Vat dye]]s''' 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 dye|indigo]], the original vat dye.
+==== Functional dyes ====
+While conventional dyes are used to modify the appearance of textiles, leather, and paper, functional dyes generally serve non-aesthetic purposes. Typical applications include [[Indicator (disambiguation)|indicator dyes]] or [[voltage-dependent dyes]].<ref name="Griffiths">John Griffiths: ''Funktionelle Farbstoffe. Ein neuer Trend in der Farbstoffchemie''. In: ''Chemie in unserer Zeit.'' 27, Nr. 1, 1993, S.&nbsp;21–31, [[doi:10.1002/ciuz.19930270104]].</ref>
-'''[[Reactive dyes]]''' utilize a [[chromophore]] attached to a [[substituent]] that is capable of directly [[chemical reaction|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.
+Special dyes can
-'''[[Disperse dye]]s''' 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 {{convert|130|C|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.
+* absorb light at a specific wavelength and convert it into heat (e.g., in chemical and biochemical analysis),<ref name="Griffiths" />
+* re-emit absorbed light at a different wavelength (as phosphorescent biomarkers or inks, fluorescence in dye lasers, [[chemiluminescence]] in the breaking or formation of chemical bonds in biochemistry),<ref name="Griffiths" />
+* change the polarization direction of light (e.g., in frequency doubling or as optical switches),
+* induce electrical phenomena (e.g., in laser printer applications),
+* enable photochemical processes.
-'''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 [[wikt:component|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.
+[[organic dye laser|Laser dyes]] are used in the production of some lasers, optical media ([[CD-R#ORGANIC DYE|CD-R]]), and [[camera sensors]] ([[color filter array]]).<ref>{{cite book|url=https://books.google.com/books?id=_F4hAwAAQBAJ&q=organic+dye+laser&pg=PA539|title=Laser Fundamentals|first=William T.|last=Silfvast|date=21 July 2008|publisher=Cambridge University Press|access-date=8 November 2017|via=Google Books|isbn=9781139855570}}</ref> From an economic perspective, functional dyes are particularly important in the manufacture of CDs and DVDs. The dye molecules are embedded in the polycarbonate of the disc. The laser beam of the burner causes the dye molecules to absorb light energy and convert it into heat, leading to localized melting of the polycarbonate. This slightly altered surface structure is then detected during the reading process.<ref>Klaus Roth: ''Die Chemie der schillernden Scheiben: CD, DVD & Co.'' In: ''Chemie in unserer Zeit.'' 41, Nr. 4, 2007, S.&nbsp;334–345, [[doi:10.1002/ciuz.200700428]].</ref> [[Laser dye]]s are for example [[rhodamine 6G]] and [[coumarin]] dyes.<ref>{{cite book |editor1-first = F. J. |editor1-last=Duarte |editor1-link=F. J. Duarte |editor2-first=L. W. |editor2-last=Hillman |title=Dye Laser Principles |location=New York |date=1990}}</ref>
-'''[[Sulfur dye]]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]]. 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.
+==== Vital dyes ====
+A "vital dye" or stain is a dye capable of penetrating living cells or tissues without causing immediate visible degenerative changes.<ref>{{Cite web |title=Medical Definition of VITAL DYE |url=https://www.merriam-webster.com/medical/vital%20dye |access-date=2024-10-24 |website=www.merriam-webster.com}}</ref> Such dyes are useful in medical and pathological fields in order to selectively color certain structures (such as cells) in order to distinguish them from surrounding tissue and thus make them more visible for study (for instance, under a microscope). As the visibility is meant to allow study of the cells or tissues, it is usually important that the dye not have other effects on the structure or function of the tissue that might impair objective observation.
-'''Some dyes commonly used in Staining:'''
+A distinction is drawn between dyes that are meant to be used on cells that have been removed from the organism prior to study (supravital staining) and dyes that are used within a living body - administered by injection or other means (intravital staining) - as the latter is (for instance) subject to higher safety standards, and must typically be a chemical known to avoid causing adverse effects on any biochemistry (until cleared from the tissue), not just to the tissue being studied, or in the short term.
-{| class="wikitable"
-|+
-!Basic Dyes
-!Acidic Dyes
-|-
-|[[Safranin]]
-|[[Eosin]]
-|-
-|[[Fuchsine|Basic fuchsin]]
-|[[Acid fuchsin]]
-|-
-|[[Crystal violet]]
-|[[Congo red]]
-|-
-|[[Methylene blue]]
-|
-|}
-{{clear}}
-==Food dyes==
+The term "vital stain" is occasionally used interchangeably with both intravital and supravital stains, the underlying concept in either case being that the cells examined are still alive.
-One other class that describes the role of dyes, rather than their mode of use, is the [[food coloring|food dye]]. Because food dyes are classed as [[food additive]]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 [[law|legislation]]. Many are [[Azo compound|azo]] dyes, although [[anthraquinone]] and [[triphenylmethane]] compounds are used for colors such as [[green]] and [[blue]]. Some naturally occurring dyes are also used.<ref>{{cite journal |last1=Rodriguez-Amaya |first1=Delia B |title=Natural food pigments and colorants |journal=Current Opinion in Food Science |date=February 2016 |volume=7 |pages=20–26 |doi=10.1016/j.cofs.2015.08.004 }}</ref>
+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).<ref>{{cite book |last=Ionescu |first=Sinziana |url=https://www.intechopen.com/citation-pdf-url/78967 |title=Current Topics in Colorectal Surgery |date=2023-07-26 |publisher=IntechOpen |isbn=978-1-83962-335-6 |chapter=The Use of Indocyanine Green in Colorectal Surgery |doi=10.5772/intechopen.100301 |doi-access=free}}{{CC-notice|by3}}</ref>
-==Other important dyes==
+==== Other important dyes ====
 A number of other classes have also been established, including:
-* Oxidation bases, for mainly hair and fur
-* [[Laser dye]]s: [[rhodamine 6G]] and [[coumarin]] dyes.<ref>{{cite book |editor1-first = F. J. |editor1-last=Duarte |editor1-link=F. J. Duarte |editor2-first=L. W. |editor2-last=Hillman |title=Dye Laser Principles |location=New York |date=1990}}</ref>
 * [[Leather]] dyes, for leather
 * [[Fluorescent brightener]]s, for textile fibres and paper
@@ Line 87: / Line 297: @@
 * Mayhems dye, used in water cooling for looks, often rebranded RIT dye
-==Chromophoric dyes==
+== Pollution ==
-By the nature of their [[chromophore]], dyes are divided into:<ref>{{cite web|url=http://stainsfile.info/StainsFile/dyes/dyes.htm|title=Stainsfile - Dye index|first=Bryan D.|last=Llewellyn|website=Stainsfile.info|access-date=8 November 2017|archive-url=https://web.archive.org/web/20080416165706/http://stainsfile.info/StainsFile/dyes/dyes.htm|archive-date=16 April 2008|url-status=dead}}</ref>
+Dyes produced by the textile, printing and paper industries are a source of pollution of rivers and waterways.<ref name=Brindley2009>{{cite news |last= Brindley |first=Lewis |date=July 2009 |title= New solution for dye wastewater pollution |url= https://www.chemistryworld.com/news/new-solution-for-dye-wastewater-pollution/3002870.article|work= [[Chemistry World]]|access-date=2018-07-08}}</ref> 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.<ref>{{cite journal|doi=10.1016/j.chemosphere.2004.07.030|title=Degradation of dyes in aqueous solutions by the Fenton process|year=2004|last1=Xu|first1=Xiang-Rong|last2=Li|first2=Hua-Bin|last3=Wang|first3=Wen-Hua|last4=Gu|first4=Ji-Dong|journal=Chemosphere|volume=57|issue=7|pages=595–600|pmid=15488921|bibcode=2004Chmsp..57..595X|url=http://ir.rcees.ac.cn/handle/311016/23586|url-access=subscription}}</ref>
-* [[:Category:Acridine dyes]], derivates of [[acridine]]
-* [[:Category:Anthraquinone dyes]], derivates of [[anthraquinone]]
+== Dye degradation and treatment ==
-* Arylmethane dyes
+{{More citations needed section|date=February 2026}}
-** [[:Category:Diarylmethane dyes]], based on diphenyl methane
+Before being released into the environment, the dyes can be broken down into less harmful substances or separated from the water which is then released. There are several ways to do this:
-** [[:Category:Triarylmethane dyes]], derivates of [[triphenylmethane]]
-* [[:Category:Azo dyes]], based on -N=N- [[azo compound|azo]] structure
+=== Adsorption ===
-* Phthalocyanine dyes, derivatives of [[phthalocyanine]]
+[[Adsorption]] is one of the most common and effective methods for dye removal due to its simplicity, low cost, and wide availability of adsorbents. In this process, dye molecules adhere to the surface of solid materials like [[activated carbon]], clay, [[zeolite]]s, or agricultural waste. The method does not require harsh chemicals or high energy and can achieve high dye removal efficiency. However, its performance depends on the type of dye and the surface properties of the adsorbent and spent adsorbents may also require proper disposal or regeneration.
-* Quinone-imine dyes, derivatives of [[quinone]]
-** [[:Category:Azin dyes]]
+=== Membrane filtration ===
-*** [[:Category:Eurhodin dyes]]
+[[Membrane technology|Membrane filtration]] involve separation of dye molecules from water using semi-permeable membranes. Techniques such as [[ultrafiltration]], [[nanofiltration]], and [[reverse osmosis]] can remove dyes based on their size and molecular weight. These methods offer high separation efficiency and can produce reusable water. However, they can be expensive, require high pressure, and are prone to [[membrane fouling]], which reduces their lifespan and performance.
-*** [[:Category:Safranin dyes|Category:Safranih]]
-*** [[:Category:Safranin dyes|dyes]], derivates of [[safranin]]
+=== Coagulation and flocculation ===
-** Indamins
+This method uses chemical coagulants (alum, ferric chloride) to destabilize and aggregate dye particles into larger flocs. These flocs can then be removed through sedimentation or filtration. Coagulation is commonly used as a pre-treatment step in wastewater treatment plants. While effective for removing particulate-bound dyes, it is less efficient for soluble or highly stable dye compounds and generates a large volume of chemical sludge.
-** [[:Category:Indophenol dyes]], derivates of indophenol
-** [[:Category:Oxazin dyes]], derivates of oxazin
+=== Biological treatment ===
-** Oxazone dyes, derivates of [[Nile red|oxazone]]
+Biological methods rely on the activity of microorganisms (bacteria, fungi, or algae) to degrade dye molecules. These processes are cost-effective and environmentally friendly, making them attractive for large-scale treatment. However, many synthetic dyes, especially azo dyes, are resistant to microbial breakdown due to their complex structures. Biological methods often require long retention times and are sensitive to operational conditions such as pH, temperature, and the presence of toxic substances.<ref>{{Cite journal |last=Lin |first=Jiuyang |last2=Ye |first2=Wenyuan |last3=Xie |first3=Ming |last4=Seo |first4=Dong Han |last5=Luo |first5=Jianquan |last6=Wan |first6=Yinhua |last7=Van der Bruggen |first7=Bart |date=October 26, 2023 |title=Environmental impacts and remediation of dye-containing wastewater |url=https://www.nature.com/articles/s43017-023-00489-8 |journal=Nature Reviews Earth & Environment |language=en |volume=4 |issue=11 |pages=785–803 |doi=10.1038/s43017-023-00489-8 |issn=2662-138X|url-access=subscription }}</ref><ref>{{Cite journal |last=Anandita |last2=Raees |first2=Kashif |last3=Shahadat |first3=Mohammad |last4=Ali |first4=Syed Wazed |date=2023-09-06 |title=Mechanistic Interaction of Microbe in Dye Degradation and the Role of Inherently Modified Organisms: a Review |url=https://doi.org/10.1007/s41101-023-00219-7 |journal=Water Conservation Science and Engineering |language=en |volume=8 |issue=1 |pages=43 |doi=10.1007/s41101-023-00219-7 |issn=2364-5687|url-access=subscription }}</ref>
-** [[:Category:Thiazine dyes]]
-* [[:Category:Thiazole dyes]]
-* [[:Category:Safranin dyes]]
-* [[Xanthene#Xanthene dyes|Xanthene dyes]]
-** Fluorene dyes, derivatives of [[fluorene]]
-*** [[Pyronin]] dyes
-** [[:Category:Fluorone dyes]], based on [[fluorone]]
-*** [[:Category:Rhodamine dyes]], derivatives of [[rhodamine]]
-== Pollution ==
+=== Chemical oxidation ===
-Dyes produced by the textile, printing and paper industries are a source of pollution of rivers and waterways.<ref name=Brindley2009>{{cite news |last= Brindley |first=Lewis |date=July 2009 |title= New solution for dye wastewater pollution |url= https://www.chemistryworld.com/news/new-solution-for-dye-wastewater-pollution/3002870.article|work= [[Chemistry World]]|access-date=2018-07-08 }}</ref> 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.<ref>{{cite journal|doi=10.1016/j.chemosphere.2004.07.030|title=Degradation of dyes in aqueous solutions by the Fenton process|year=2004|last1=Xu|first1=Xiang-Rong|last2=Li|first2=Hua-Bin|last3=Wang|first3=Wen-Hua|last4=Gu|first4=Ji-Dong|journal=Chemosphere|volume=57|issue=7|pages=595–600|pmid=15488921|bibcode=2004Chmsp..57..595X|url=http://ir.rcees.ac.cn/handle/311016/23586|url-access=subscription}}</ref>
+Chemical oxidation uses strong oxidants such as [[ozone]] ({{chem|O|3}}), [[hydrogen peroxide]] ({{chem|H|2|O|2}}), or [[chlorine]] to break down dye molecules into less harmful substances. [[Advanced oxidation process]]es (AOPs) generate highly reactive radicals that can fully mineralize organic pollutants. These methods are fast and effective for a wide range of dyes but can be costly and may produce secondary pollutants or require complex equipment.
-==Vital dyes==
+=== Photocatalytic degradation ===
-A "vital dye" or stain is a dye capable of penetrating living cells or tissues without causing immediate visible degenerative changes.<ref>{{Cite web |title=Medical Definition of VITAL DYE |url=https://www.merriam-webster.com/medical/vital%20dye |access-date=2024-10-24 |website=www.merriam-webster.com |language=en}} </ref> Such dyes are useful in medical and pathological fields in order to selectively color certain structures (such as cells) in order to distinguish them from surrounding tissue and thus make them more visible for study (for instance, under a microscope). As the visibility is meant to allow study of the cells or tissues, it is usually important that the dye not have other effects on the structure or function of the tissue that might impair objective observation.
+[[Photocatalysis|Photocatalytic]] degradation is a sustainable and advanced method that uses light energy (usually UV or sunlight) in the presence of a semiconductor catalyst like [[titanium dioxide]] ({{chem|TiO|2}}) or [[zinc oxide]] (ZnO) to degrade dyes. The process generates [[reactive oxygen species]] (ROS) such as [[hydroxyl radical]]s that break down dye molecules into smaller and less harmful by-products such as water and carbon dioxide. This method is clean, reusable, and effective for treating resistant dyes, making it ideal for modern wastewater treatment strategies. Heterogeneous photocatalysis is one approach to the degradation of dyes.<ref>Pandit, V.K.; Arbuj, S.S.; Pandit, Y.B.; Naik, S.D.; Rane, S.B.; Mulik, U.P.; Gosavic, S.W.; Kale, B.B. Solar Light driven Dye Degradation using novel Organo–Inorganic (6,13-Pentacenequinone/TiO<sub>2</sub>) Nanocomposite". RSC Adv. 2015, 5, 10326-10331.</ref><ref>{{Cite journal |last=Khan |first=Sadia |last2=Noor |first2=Tayyaba |last3=Iqbal |first3=Naseem |last4=Yaqoob |first4=Lubna |date=2024-05-21 |title=Photocatalytic Dye Degradation from Textile Wastewater: A Review |url=https://doi.org/10.1021/acsomega.4c00887 |journal=ACS Omega |volume=9 |issue=20 |pages=21751–21767 |doi=10.1021/acsomega.4c00887  |doi-access=free|pmc=11112581 |pmid=38799325}}</ref>
-A distinction is drawn between dyes that are meant to be used on cells that have been removed from the organism prior to study (supravital staining) and dyes that are used within a living body - administered by injection or other means (intravital staining) - as the latter is (for instance) subject to higher safety standards, and must typically be a chemical known to avoid causing adverse effects on any biochemistry (until cleared from the tissue), not just to the tissue being studied, or in the short term.
+=== Ion exchange ===
+In ion exchange, dye ions in water are exchanged with non-toxic ions using synthetic resin materials. This method is selective, efficient, and works well for low-concentration dye solutions. It can also be regenerated and reused multiple times. However, its capacity is limited, and it is less effective for removing large, non-ionic, or complex dye molecules.
-The term "vital stain" is occasionally used interchangeably with both intravital and supravital stains, the underlying concept in either case being that the cells examined are still alive.
+=== Electrochemical treatment ===
-In a stricter sense, the term "vital staining" means the polar opposite of "supravital staining."
+Electrochemical treatment uses electric current to drive oxidation or reduction reactions that break down dye molecules. It can be performed without additional chemicals and is capable of complete dye removal. The process is effective for a wide range of dyes and can be automated. However, it requires high energy input, and the equipment can be costly for large-scale operations.
-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).<ref>{{cite book | last=Ionescu | first=Sinziana | title=Current Topics in Colorectal Surgery | chapter=The Use of Indocyanine Green in Colorectal Surgery | publisher=IntechOpen | date=2023-07-26 | isbn=978-1-83962-335-6 | doi=10.5772/intechopen.100301 | doi-access=free | url=https://www.intechopen.com/citation-pdf-url/78967 }}{{CC-notice|by3}}</ref>
 ==See also==
@@ Line 153: / Line 354: @@
 * 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)
-*{{Cite web |title=Synthetic Dye - an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/engineering/synthetic-dye |access-date=2022-11-18 |website=www.sciencedirect.com}}
 {{Dyeing}}