- Key People:
- Friedrich Bayer
- Adolf von Baeyer
- Related Topics:
- methylene green
- logwood
- mordant
- substantivity
- acetate dye
dye
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What is a dye?
A dye is a substance that adds color to materials like textiles, paper, and leather, and resists fading from washing, heat, or light. Most dyes are organic compounds.
Dyeing involves immersing the material in a solution called a dyebath, where dye molecules attach through absorption and different forces. To ensure the coloring is permanent, the dye molecules must bond to the fiber. Heat helps transfer dye molecules from the solution to the fiber.
The first synthetic dye, mauve, was discovered in 1856, which led to the creation of many more synthetic dyes. Today, dyes are typically used in combination to achieve a desired color.
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How are dyes different from pigments?
Dyes and pigments both add color to materials, but they differ in composition and application. Dyes are coloring substances used to impart color to textiles, paper, leather, and other materials. Most dyes are organic compounds, containing carbon, while pigments can be inorganic (without carbon) or organic.
Pigments are finely ground, insoluble solid particles mixed with a liquid. They are applied as dispersions rather than solutions. Dyes, in contrast, must closely associate with a material to give even coloring and resist moisture, heat, and light. Some pigments are dyes that have been rendered insoluble through a chemical reaction.
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What materials can be colored using dyes?
Dyes color textiles, paper, leather, and other materials by imparting color that resists alteration from washing, heat, light, or other factors. Unlike pigments, which are finely ground solids dispersed in a liquid, dyes are usually organic compounds.
Most textile materials can be dyed at almost any stage of production. The selection of dye depends on the material and specific requirements, such as lightfastness. Effective preparation of the material for dyeing is essential.
Different types of dyes are used for various fibers:
* Acid dyes for wool, silk, and nylon
* Direct dyes for cellulose fibers
* Mordant dyes for cellulosic fibers, wool, or silk
* Sulfur dyes for cellulose
* Azoic dyes for insoluble pigments within the fiber
* Vat dyes for cellulose, which become soluble and then oxidize to an insoluble pigment
* Disperse dyes for hydrophobic fibers like polyesters, nylon, and cellulose acetates
* Reactive dyes combine directly with the fiber, resulting in excellent colorfastness.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do natural and synthetic dyes compare?
Until the late 19th century, dyes were exclusively natural, derived from plants, insects, and mollusks. These dyes, when enhanced with chemicals like alum, proved durable and beautiful, showcasing subtle color variations known as abrash.
The advent of synthetic aniline dyes in the 19th century initially gained popularity for their quick application and brilliance. However, their poor durability and garish colors led many artisans to revert to natural dyes. Although synthetic dyes have improved in fastness and subtlety, natural dyes are still preferred. Today, the only natural dye still used commercially to a small degree is logwood.
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How are dyes applied to fabrics or other surfaces?
Dyes are applied to fabrics and other surfaces through various methods, with the goal of achieving level and lasting color. The process involves both chemical and physical interactions between the dye and the material.
Application Techniques:
* Direct Dyeing: Fabric is immersed in a hot aqueous solution to improve dye solubility and fabric wettability.
* Disperse Dyeing: Used for hydrophobic synthetic fibers, this method involves immersing the fabric in an aqueous dispersion of insoluble dyes.
* Azo Dyeing: Azoic diazo and coupling components are used to generate dyes directly on the fabric for improved fastness.
* Textile Printing: Pigments and dyes are applied to textile fabrics in patterns using methods such as block, roller, screen, and heat transfer printing.
* Solvent Dyeing: Water is replaced by solvents to achieve more rapid wetting of textiles, less swelling, increased dyeing speed, and energy savings.The selection of dyes depends on the material type and specific requirements like lightfastness and cost. After color application, fixation (usually steaming or heating) is performed, followed by washing to remove excess dye.
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What are some of the environmental impacts of dye production and use?
The production and use of dyes can create significant environmental problems. The discharge of liquid waste into water and drainage systems can contribute to environmental degradation. Traditional dyeing methods can lead to effluent (pollution) problems. In the informal sector, toxic chemicals with no economic value are sometimes dumped during the recycling process. This toxic industrial effluent can affect local groundwater quality, making the water unfit for consumption or agriculture. Dismantling activities can cause atmospheric pollution as dust particles loaded with heavy metals and flame retardants enter the atmosphere, potentially polluting soil and water systems.
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dye, substance used to impart colour to textiles, paper, leather, and other materials such that the colouring is not readily altered by washing, heat, light, or other factors to which the material is likely to be exposed. Dyes differ from pigments, which are finely ground solids dispersed in a liquid, such as paint or ink, or blended with other materials. Most dyes are organic compounds (i.e., they contain carbon), whereas pigments may be inorganic compounds (i.e., they do not contain carbon) or organic compounds. Pigments generally give brighter colours and may be dyes that are insoluble in the medium employed.
Colour has always fascinated humankind, for both aesthetic and social reasons. Throughout history dyes and pigments have been major articles of commerce. Manufacture of virtually all commercial products involves colour at some stage, and today some 9,000 colorants with more than 50,000 trade names are used. The large number is a consequence of the range of tints and hues desired, the chemical nature of the materials to be coloured, and the fact that colour is directly related to the molecular structure of the dye.
History of dyes
Natural dyes
Until the 1850s virtually all dyes were obtained from natural sources, most commonly from vegetables, such as plants, trees, and lichens, with a few from insects. Solid evidence that dyeing methods are more than 4,000 years old has been provided by dyed fabrics found in Egyptian tombs. Ancient hieroglyphs describe extraction and application of natural dyes. Countless attempts have been made to extract dyes from brightly coloured plants and flowers; yet only a dozen or so natural dyes found widespread use. Undoubtedly most attempts failed because most natural dyes are not highly stable and occur as components of complex mixtures, the successful separation of which would be unlikely by the crude methods employed in ancient times. Nevertheless, studies of these dyes in the 1800s provided a base for development of synthetic dyes, which dominated the market by 1900.
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Two natural dyes, alizarin and indigo, have major significance. Alizarin is a red dye extracted from the roots of the madder plant, Rubia tinctorium. Two other red dyes were obtained from scale insects. These include kermes, obtained from Coccus ilicis (or Kermes ilicis), which infects the Kermes oak, and cochineal, obtained from Dactylopius coccus, which lives on prickly pear cactus in Mexico. One kilogram (2.2 pounds) of cochineal dye can be obtained from an estimated 200,000 insects. The principal coloured components in these dyes are kermesic and carminic acids, respectively, whose similarity was established by 1920. In their natural state many colorants are rendered water-soluble through the presence of sugar residues. These sugars, however, are often lost during dye isolation procedures.
Probably the oldest known dye is the blue dye indigo, obtained in Europe from the leaves of the dyerswoad herb, Isatis tinctoria, and in Asia from the indigo plant, Indigofera tinctoria. Even by modern standards, both alizarin and indigo have very good dyeing properties, and indigo remains a favoured dye for denim, although synthetic indigo has replaced the natural material.
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With a process developed by the Phoenicians, a derivative of indigo, Tyrian purple, was extracted in very small amounts from the glands of a snail, Murex brandaris, indigenous to the Mediterranean Sea. Experiments in 1909 yielded 1.4 grams (0.05 ounce) from 12,000 snails. Historically, this dye was also called royal purple because kings, emperors, and high priests had the exclusive right to wear garments dyed with it, as is well documented in the Hebrew Bible and illustrated for Roman emperors on mosaics in Ravenna, Italy. By the 1450s, with the decline of the Eastern Roman Empire, the Mediterranean purple industry died out.
Natural yellow dyes include louting, from the leaves of weld, Reseda luteola, and quercetin, from the bark of the North American oak tree, Quercus tinctoria. These are in the flavonoid family, a group of compounds occurring almost exclusively in higher plants and producing the colours of many flowers. In fact, these compounds can produce all the colours of the rainbow except green. Luteolin, a yellow crystalline pigment, was used with indigo to produce Lincoln green, the colour associated with Robin Hood and his merry men.
Another group of compounds, the carotenoids, present in all green plants, produce yellow to red shades. Lycopene, from which all carotenoids are derived, produces the red colour of tomatoes. An ancient natural yellow dye, crocetin, was obtained from the stigmas of Crocus sativus; this dye is undoubtedly derived from lycopene in the plant. Few of the flavonoid and carotenoid colorants would have survived ancient extraction processes.
Logwood is the only natural dye used today. Heartwood extracts of the logwood tree, Haematoxylon campechianum, yield hematoxylin, which oxidizes to hematein during isolation. The latter is red but in combination with chromium gives shades of charcoal, gray, and black; it is used mainly to dye silk and leather.
Mordants
Highly skilled craftsmen with closely guarded secret formulas rendered dyeing a well-protected trade. The formation of different colours by mixing red, blue, and yellow dyes was well known in ancient times, as was the use of metal salts to aid the retention of dyes on the desired material and to vary the resultant colours. Natural dyes cannot be applied directly to cotton, in contrast to wool and silk, although cotton can be dyed by vatting or by pretreatment with inorganic salts known as mordants (from Latin mordere, meaning “to bite”). These are adsorbed on the fibre and react with the dye to produce a less soluble form that is held to the fabric. Alum, KAl(SO4)2 × H2O, as well as iron, copper, and tin salts were common ancient mordants. No doubt the secret processes included other ingredients to improve the final results. Mordants also were used to vary the colours produced from a single dye. For example, treatment with aluminum hydroxide, Al(OH)3, before dyeing with alizarin produces Turkey red, the traditional red of British and French army uniforms. Alizarin gives violet colours with magnesium mordants, purple-red with calcium mordants, blue with barium mordants, and black-violet with ferrous salts. Around 1850, chromium salts, used as mordants, were found to provide superior dye retention and, in time, largely displaced the others; chromium mordants are still widely used for wool and, to some extent, for silk and nylon.
Decline of natural dyes
Until 1857 the dye industry utilized natural dyes almost exclusively; however, by 1900 nearly 90 percent of industrial dyes were synthetic. Several factors contributed to the commercial decline of natural dyes. By 1850 the Industrial Revolution in Europe led to a burgeoning textile industry, which created increased demand for readily available, inexpensive, and easily applied dyes and revealed the important economic limitations of natural dyes. Since most dyes were imported from distant sources, transportation delays were likely to slow the production of dyed materials. Dye quality was affected by the whims of nature and the dye maker’s skills. In addition, inefficient processes were often required for optimum results; for example, Turkey red dyeing could involve more than 20 steps to produce the desired bright, fast colour. Advances in organic chemistry, both practical and theoretical, spurred by studies of the many new compounds found in coal tar, increased interest in finding ways to utilize this by-product of coke production. The dye industry played a major role in the development of structural organic chemistry, which in turn provided a sound scientific foundation for the dye industry.