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Dyes and fibres the assembly of materials and their coloration precedes recorded history. many cultures had established coloring technologies before 3000 B.C.. These ancient artisans remodeled the offered natural fibres – linen, cotton, wool and silk – into materials, initially by hand, and later victimization easy mechanical devices. Short fibres were 1st carded or combed, to put them parallel to at least one another. Drawing out of a band of combed fibres by pull, with gradual twisting, created yarn. Finally, yarns were reticulated to create a woven material. The techniques used hardly modified till the economic Revolution, after they became totally mechanised. though finely ground, colored minerals, distributed in water, were utilized in paints over thirty 000 years past, they simply washed off any material colored with them. Natural dyes were extracted from plant and animal sources with water, generally beneath conditions involving fermentation. material was coloured by soaking it within the liquid extract and drying. These dyes had solely a restricted vary of lifeless colors and therefore the dyeings invariably had poor fastness to laundry and daylight. The fastness of a coloring could be a live of its resistance to weakening, or color amendment, on exposure to a given agency or treatment. Most natural dyes conjointly lacked substantivity for fibres like wool and cotton. Substantivity implies some attraction of the dye for the fibre, so the dye within the answer step by step becomes depleted because fiber absorb this. The bad fastness properties of natural dyes usually improved if the material was 1st treated with an answer containing a salt of, as an example, iron, copper or tin. The conditions used favoured combination of the metal ions with the actual fibre, or their precipitation within it. These metal salts were referred to as mordants. once the pre-mordanted material was soaked in a very tub of an appropriate natural dye, the dye absorbed into the fibres and reacted with the metal ions gift. This reaction weakened the water solubility of the dye therefore the color was less probably to bleed out on laundry. The word ‘mordant’ originated from the French verb mordre that means ‘to bite’. In Chapter thirteen, we have a tendency to shall see that the thought of the dye biting the mordant, to create a stable dye–metal advanced, could be a helpful description. In fashionable coloring procedures, the dye reacts with the mordant within the fibre in a very separate method once coloring, or the metal is incorporated into the colouring material throughout its manufacture. many natural dyes gave higher quality dyeings of cotton or wool, however concerned long and tough processes. as an example, the colorant extracted from madder root, from the plant genus Rubia tinctorium, coloured cotton pre-mordanted with atomic number 13 and atomic number 20 salts to offer the notable redness. victimization associate iron mordant, an equivalent colorant gave a purplish-black. Indigo, extracted from leaves of the plant shrub, and Tyrian Purple from sea snails of the genera Murex and peliosis, ar waterinsoluble pigments referred to as vat dyes. These don’t need mordants. throughout the time of the empire, wool material coloured with Tyrian Purple was therefore extremely prized that solely the upper class wore clothes created with it. For coloring with Indigo, a soluble, reduced variety of the dye was 1st obtained by extraction and fermentation. the method became referred to as vatting, from the name of the vessels used – therefore the term ‘vat dye’. The soluble, reduced variety of the dye is termed a leuco by-product. Leuco Indigo has substantivity for wool and cotton fibres. once coloring, air oxidisation of the yellowness leuco dye, absorbed within the fibres, regenerates the navy blue, insoluble pigment at bay within them. as a result of this, the fastness to laundry is incredibly smart compared to most natural dyes. Scheme 1.1 outlines the essential steps in vat coloring.
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