Indigo natural color

With the exception of aluminum, which is one of the most abundant elements in Earths crust, most of the boron group elements are rare. None of the elements are found free in nature. Three can be identified by flame tests, as shown in the table. Boron produces a bright green color, while indium produces an indigo blue color. Thallium produces a green color. More precise identification methods involve advanced spectral and imaging techniques. 

N.p. were used in antiquity as dyes. Among the oldest of these arc alizarin, indigo, tyrian purple, sa-ffan, keimes, crxdiineal and many flavonoid-contain-ing colored woods. In the dyeing industry they have now been largely replaced by superior synthetic com-potmds, but natural coloring materials are still used in the food industry. 

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). 

Piesendy, all ceitified colois aie factory-piepaied materials belonging to one of several different chemical classes. Although a few such as D C Blue No. 6 (indigo) are known to exist in nature, certified colors owe their commercial importance to their synthetic production. Because of the starting materials used in their manufacture in the past, certified colors were once known as coal-tar dyes. Today, since most of the raw materials used in their preparation are obtained from petroleum, this term no longer appHes. 

Humans have used dyes to create color since the dawn of history. Until the mid-nineteenth century, all dyes were of natural origin. Many came from plants, such as indigo, a dark blue dye that was extracted from the leaves of a native East Indian plant. In 1856, the young English chemist William Perkin stumbled upon the first synthetic dye. Perkin was trying to synthesize quinine, a valuable antimalaria dmg. None of his experiments met with success. As he was about to discard the residue from yet another failed reaction, Perkin noticed that it was colored with a purple tinge. He washed the residue with hot alcohol and obtained a purple solution from which strikingly beautiful purple crystals precipitated. Perkin had no idea what the substance was or what reactions had created it, but he immediately saw its potential as a new dye. 

Indigo (57), the parent system of this group of colorants, is one of the oldest known natural dyes (see Chapter 1). The naturally occurring... 

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... 

K. Pawlak, M. Puchalska, A. Miszczak, E. Rosloniec and M. Jarosz, Blue natural organic dyestuffs from textile dyeing to mural painting. Separation and characterization of coloring matters present in elderberry, logwood and indigo, J. Mass Spectrom., 41, 613 622 (2006). 

In the flourishing chemical industry of the 1800, novel dye syntheses played a very significant role. The synthesis of indigo, the king of dyes , was a particular challenge. The motivation was partly academic curiosity as to the nature of the unknown coloration principle involved. But the economic interest of being able to produce this 5000-t/a dye more cheaply and in higher quality also provided a powerful impetus. 

Representative optical spectra of various sapphires are illustrated in fig. 4.16. It is apparent from the spectra of the natural blue sapphire (fig. 4.16b) that absorption minima in the violet-indigo and blue-green regions, which are located between sharp peaks at 25,680 cm-1 and 22,220 cm-1 and broad bands spanning 17,800 to 14,200 cm-1, are responsible for the blue coloration. Absorption at 17,800 to 14,200 cm-1 is less intense in spectra of natural yellow sapphire (fig. 4.16a see also fig. 3.21) containing negligible Ti. The spectra of synthetic Ti3+-doped A1203 (fig. 4.16c) show absorption maxima at... 

Most textiles found in historic museums are natural fibers dyed with natural dyestuffs. Therefore, in this experiment two common textiles, cotton and wool, were dyed with safflower, madder root, logwood chips, and indigo. These dyes were chosen to represent a range of colors often found in historic textiles. The cotton and wool textiles were obtained... 

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