Mordant dyes natural

Acid dyes Azoic colouring matters Basic dyes Developers Direct dyes Disperse dyes Fluorescent dyes Food dyes Ingrain dyes Leather dyes Mordant dyes Natural dyes Oxidation dyes Pigments Reactive dyes Reducing agents Solvent dyes Sulphur dyes Condense sulphur dyes Vat 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). 

In mordant dyes, phenols, naphthols, and enolizable carbonyl compounds, such as pyrazolones, are generally the couplers. As a rule, 2 1 metal complexes are formed ia the afterchroming process. A typical example of a mordant dye is Eriochrome Black T (18b) which is made from the important dyestuff iatermediate nitro-l,2,4-acid, 4-amiQO-3-hydroxy-7-nitro-l-naphthalenesulfonic acid [6259-63-8]. Eriochrome Red B [3618-63-1] (49) (Cl Mordant Red 7 Cl 18760) (1, 2,4-acid — l-phenyl-3-methyl-5-pyrazolone) is another example. The equiUbrium of the two tautomeric forms depends on the nature of the solvent. 

Mordant dyes have hydroxy groups in their molecular stmcture that are capable of forming complexes with metals. Although a variety of metals such as iron, copper, aluminum, and cobalt have been used, chromium is most preferable as a mordant. Alizarin or Cl Mordant Red 11 [72 8-0] (1) (Cl 58000), the principal component of the natural dye obtained from madder root, is the most typical mordant dye (see Dyes, natural). The aluminum mordant of alizarin is a well-known dye by the name of Turkey Red and was used to dye cotton and wool with excellent fastness. However, as is the case with many other mordant dyes, it gave way to the vat or the azoic dyes, which are applied by much simpler dyeing procedures. 

Mordant Dyes. This group includes many natural as well as synthetic dyes. They have no or low substantivity for textile fibers and are therefore appHed to ceUulosic or protein fibers that have been treated (mordanted) with metallic oxides to give points of attraction for the dye. The dye... 

A large number of naphthoquinone and benzoquinone dyes occur naturally as plant constituents, and in the past many of these have found use as colorants. The chemistry of synthetic analogues began with the discovery of naphthazarin (1) [475-38-7] by Roussin in 1861. Naphthazarin and its derivatives first found use as black chrome mordant dyes for wool and silk. In contrast to the naphthoquinones, synthetic benzoquinone dyes are few in number and are generally of the... 

The use of both natural and synthetic mordant dyes has long passed its zenith. Synthetic mordant dyes are still listed as leather dyes in the Colour Index. These are chiefly monoazo dyes, which are used especially for prechromed wool. For leather, the operations involved in the metallization step are too complex and time-consuming. Nowadays, modem tanneries prefer premetallized dyes. 

In the past, the root bark was traded in the form of dark red or brown chips with a dye content of 8-10% under the names "pitti", "raktapitta" or "pappali" as a natural dye (6). The root bark was used as mordant dye for cotton, wool and silk, and produced a purple-red, bordeaux-red, brown-purple, or gray to blach shade, depending on the type of mordant used (60). 

Most of the natural dyes treated in this manner bleed only lightly or not at all because they belong to the class of mordant dyes and are present in the dyeings as sparingly soluble color lakes of aluminum, iron, or chromium and, in a few cases, as copper or tin lakes. 

In dyeing with natural mordant dyes, widely varying shades are usually obtained, depending on the mordant that was used to pretreat the textile material to be dyed. Madder dyeings on an alum mordant are red, whereas those on an iron sulfate mordant are brown-violet to violet. 

Old dyeing recipes sometimes recommend that a dyeing be obtained in a different shade by aftertreating a mordant dyeing with a different mordant. This possibility of conversion also can be used for identifying natural mordant dyes. This identification is done by boiling small... 

The group includes many natural and synthetic dyes, the latter usually being obtained from anthracene. They have no natural affinity for textiles but are applied to cellulosic or protein fibres which have been mordanted previously with a metallic oxide. The acid mordant dyes are a special class of dyes applied to wool or polyamide fibres as if the were acid dyes, and then given very high wet-fastness by subsequent mordanting. 

The mordant dyes are capable of combining with metallic ovides to form insoluble coloured lakes. Many of the old natural dyes siurli as. Mizarin, Logwood, Weld, and rustic were dyed on libres which had ]ire iously been impregnated, or mordanted, with hydroxides of chromium, tin, or aluminium. Some of these natural products v ere replaced by their synthetic equivalents and, after the structure of Alizarin had been determined, the range was increased by the addition of many analogous substances derived from anthraquinone. 

There was a time when few naturally-occurring dyes w ere of greater importance than madder because of its extensive use for dyeing bright red shades. The best madder red was dyed in Turkey and, from this, the name Turkey Red ultimately became a general term for all comparatively fast dyeings in this colour. The active mordant dye in madder is Alizarin, extracted from the root of the plant which was cultivated extensively in southern Europe, the Middle East, and Asia. It w as demonstrated by Graebe and Liebermann in 1868 that Alizarin was 1 2 dihydroxyanthra-quinone, (3) ... 

A naturally-occurring mordant dye, used extensively until a few years ago, and now probably the only one still in use, is logwood. It yields a navy blue or a black, with what is called a good bloom, when dyed on chrome mordanted wool. Until the advent of acid mordant dyes, which will be described later, it was the only dyestuff with which wool could be dj ed black with any measure of fastness. 

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