Plants natural dyes

Textile dyes were, until the nineteenth century invention of aniline dyes, derived from biological sources plants or animals, eg, insects or, as in the case of the highly prized classical dyestuff Tyrian purple, a shellfish. Some of these natural dyes are so-caUed vat dyes, eg, indigo and Tyrian purple, in which a chemical modification after binding to the fiber results in the intended color. Some others are direct dyes, eg, walnut sheU and safflower, that can be apphed directly to the fiber. The majority, however, are mordant dyes a metal salt precipitated onto the fiber facUitates the binding of the dyestuff Aluminum, iron, and tin salts ate the most common historical mordants. The color of the dyed textile depends on the mordant used for example, cochineal is crimson when mordanted with aluminum, purple with iron, and scarlet with tin (see Dyes AND DYE INTERMEDIATES). 

With the increased awareness of environmental and green issues there has been an increased interest in natural dyes accompanied by a lobby for natural fibers in favor of synthetic fibers. However, studies have shown (3) that if 1990 s volume of cotton were colored with natural dyes, at least 31% of the available world s agricultural land would be needed to cultivate the requisite plants. The estimate is based on it taking, on average, 440 g of fresh dye plant to achieve the same tinctorial effect as 1 g of synthetic dye. 

Contrary to proponents assumptions, natural dyes are not necessarily environmentally friendly. First, large amounts of plant waste would be produced because of the low dye content in plants, eg, 170 million t of waste to color the cotton volume. Also, in order to dye fabric with natural dyes, "mordants," which are usually based on heavy metals, have to be used. For example, madder is appHed with tin (Sn) or aluminum (Al). Weld is appHed with tin salts. Salts based on copper and iron can also be used. 

The anthraquinone stmcture occurs in both the plant and animal kingdom. Those natural dyes having this stmcture surpass all other natural dyes in fastness properties (see Dyes, anthraquinone). 

Alizarin. There is only one significant plant anthraquinone dye, alizariu [72-48-0] (Cl Natural Red 6, 8, 9,10, 11, and 12 Cl 75330). In ancient times, alizaria was the preferred red dye. Cloth dyed with it has been found in Egyptian tombs dating 6000 years ago. The dye is found in the madder plant, a member of the Rubiaceae family. In 1944 about 35 species of this plant were known (1), but the use of more sophisticated analytical methods led to the detection of many more species by 1984 the number had increased to 50 (2). Of these, tinctorum and R peregrina yield the greatest amount of dye,... 

This noble but naive attempt - bearing in mind that only the molecular formula of C20H24N2O2 was known at the time - was doomed to fail. In subsequent experiments with aniline, which was fortunately contaminated with toluidines, Perkin obtained a purple product in low yield. Perkin was quick to recognize the commercial potential of his findings the natural dye, Tyrian purple, which was extracted from a species of Mediterranean snail, cost more per kilogram than gold in 1856. Within a few years the first commercial plant for the production of mauveine was in operation. 

The natural dyes industry was also a large, sophisticated, and worldwide employer. Master dyers made a wide range of reasonably fast colors and handed down secret dye recipes to their apprentices. Europe s two staple dyes were madder red from the Mediterranean and indigo blue from India. Other natural dyes included violet from lichens dark red from the forget-me-not family brown from African aloe plants and black from tumorlike... 

Only natural dyes were known until the nineteenth century. By trial and error and probably also by chance, humans learned to extract and use a large variety of dyes of vegetable and animal origin. Dyes were extracted from the roots, trunk bark, and branches of trees, the stems, leaves, flowers, and fruits of plants, the bodies of insects and mollusks, and the eggs of insects. All the dyes obtained from natural sources are rather impure, and hence the accurate reproducibility of colors was almost impossible during antiquity. Still, many of the dyes and dyeing techniques used in antiquity were highly developed and remained in use until the discovery of the synthetic dyes in the middle of the nineteenth century (Colombo 1995 Robinson 1969). 

The methods used for making pigments from these and other natural dyes were more like recipes than scientific procedures and were probably derived from the work of alchemists and herbalists. The former spent their lives trying to prepare gold by dissolving all kinds of cheap substances in acids and then re-precipitating them (hence their discovery of many precipitants), while the latter sought to extract compounds of medicinal value from plants and some of their extracts must have included natural dyes. 

Flavone or 2-Phenylchromone, C15H10°2> and other flavones are the parents of a > number of yel natural dyes found in plants, leaves, fruits and flowers. The natural materials contain OH groups and occur un combined or as glucosides. Nitration occurs in 2-phenyl group giving a mixture of 2y- ... 

In addition to organic dyes, natural dyes extracted from plants can be used as photosensitizers [36,140,141]. A nanocrystalline 2 solar cell using a san-talin dye extracted from red sandalwood can produce 1.8% efficiency under 80 mW/cm2 irradiation [141]. Cherepy et al. reported that a nanocrystalline 2 solar cell using flavonoid anthocyanin dyes extracted from blackberries could convert sunlight to electrical power with an efficiency of 0.6% (Jsc = 1.5-2.2 mA/cm2 and Voc = 0.4-0.5 V) under AM 1.5 [36]. 

Important indole derivatives (see Scheme 2) include (i) indigo, a vat dye known and widely used since antiquity, and originally obtained from indican, a (3-glucoside of indoxyl which occurs in some plants. Indigo is now prepared synthetically. Tyrian purple, a natural dye used since classical times, is 6,6 -dibromoindigo (ii) the numerous indole alkaloids, with complex derivatives such as yohimbine and strychnine (iii) tryptophan, an essential amino acid found in most proteins. Its metabolites include skatole and tryptamine and (iv) 3-indoleacetic acid, which is important as a plant growth hormone. 

Natural dyes comprise those colors derived from plant or animal matter without chemical processing. Modem Icsts have verified the safety of natural dyes as food colorants many of these dyes are on the FDA s list of approved food dyes. 

In preindustrial times, textiles were dyed primarily with plant dyes. Dyeing with animal dyes (kermes, Tyrian purple) was restricted to special cases. Today, synthetic dyes are used almost exclusively. However, use of natural dyes is again increasing [1, 2, 3, 4],... 

NATURAL DYES FROM PLANTS USED AS HAIR COLORANTS... 

Kramer, J. Natural Dyes Plants and Processes Scribners New York,... 

To gain a better understanding of the effect of protein fiber type, dye, and mordant on sunlight and burial weathering processes, we dyed wool and silk with three phenolic dyes (found as major components in natural dye mixtures extracted from various plant sources) and post-mordanted samples of the dyed fabrics with five representative metal salts. We then exposed the unmordanted and the dyed-mordanted samples to simulated sunlight or soil burial and measured the differences in the color and tensile properties that resulted from these treatments. 

As mentioned earlier, any information obtained from the artifacts of a preliterate society helps us to understand them. There is another very important reason to determine the nature of the dyes used in museum textiles. This applies particularly to textiles which are to be exhibited. Thanks to the work of Padfield and Landi (15), we have a reasonable amount of information about the lightfastness of natural dyes. With some exceptions, indigo, madder, and cochineal are the most important they have relatively poor lightfastness. We shall have to determine the fastness of the yarns dyed from Peruvian plants. When we know these facts, we can then help the curator or conservator to make decisions regarding exhibition, lighting, conditions of storage, and safety of conservation treatments. 

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