Textile fibers indigo

Another synthetic route proposed by von Baeyer began with o-nitrocinnamic acid (7) and led to o-nitrophenylpropiolic acid (8), which could be converted to indigo directly on the textile fiber with mild reducing agents under alkaline con-... 

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). 

In contrast to some naturally occurring dyes like indigo or kermes, which must be vatted or mordanted to be applied in textile dyeing, direct or substantive dyes can be used on cellulosic fibers directly . Their use is widespread because of their easy handling. Today, direct dyes still account for ca. 10% of the world textile dye consumption. For use on paper, see Section 5.3. Recent research on direct dyes concentrated on the replacement of possibly carcinogenic benzidine dyes [44],... 

Indigoid vat dyes are derivatives of indigo and thioindigo (see Section 3.5). Leucoindigo compounds have a comparatively low affinity for fibers. Thus, these dyes are used mainly in textile printing rather than dyeing (see Section 4.4.6). 

Beside indigo itself, the indigoid colorant thioindigo and its derivatives are also important vat dyes, but because of the low affinity of vatted thioindigo dyes for the fiber, these dyes are used mainly in textile printing. 

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... 

In examining these samples, we found evidence of indigo and a red dye in several samples, and the same red dye was found in other fibers. A search of our files of modern dyes showed this to be similar to the modem food colorant. Carmine Cl Natural Red 4, which is obtained from the cochineal insect Dactylopius cacti (formerly called Coccus cacti). Since it is believed that cochineal was known to the Precolumbian Peruvians, we made the comparison, and the curves are shown in Figure 5. Later, we found that William J. Young of the Museum of Fine Arts in Boston had found cochineal in Nazca textiles (12). 

Indigo belongs to that class of dyes commonly known as vat dyes. Generally, dyes of this type are sold as solid materials in the forms of cakes or powders that are insoluble in aqueous media. In order to solubilize the material, it needs to be first reduced to the leuco acid intermediate which is nearly colorless, then to the soluble leuco salt in the presence of an alkali (in ancient times from wood ash, plant ash or eggshells). The textile to be dyed is then immersed in this solution, and upon exposure to air, the dye will re-oxidize to the pigment within the fibers of the textile. The material can be successively dyed to produce a deeper color. 

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