dye any substance, natural or synthetic, used to color various materials, especially textiles, leather, and food. Natural dyes are so called because they are obtained from plants (e.g., alizarin , catechu , indigo , and logwood), from animals (e.g., cochineal , kermes, and Tyrian purple), and from certain naturally occurring minerals (e.g., ocher and Prussian blue ). They have been almost entirely replaced in modern dyeing by synthetic dyes. Most of these are prepared from coal tar, being formed from an aromatic hydrocarbon such as benzene, from which indigo is derived (see also aniline ), or anthracene, which yields alizarin. Although some materials, e.g., silk and wool, can be colored simply by being dipped in the dye (the dyes so used are consequently called direct dyes), others, including cotton, commonly require the use of a mordant (see also lake ). Alizarin is a mordant dye and the color it gives depends upon the mordant used. Dyes are classified also as acidic or basic according to the medium required in the dyeing process. A vat dye, e.g., indigo, is so called from the method of its application; it is first treated chemically so that it becomes soluble and is then used for coloring materials bathed in a vat. When the materials become impregnated with the dye, they are removed and dried in air, the indigo reverting to its original, insoluble form. The process by which a dye becomes "attached" to the material it colors is not definitely known. One...
dye any substance, natural or synthetic, used to color various materials, especially textiles, leather, and food. Natural dyes are so called because they are obtained from plants (e.g., alizarin , catechu , indigo , and logwood), from animals (e.g., cochineal , kermes, and Tyrian purple), and from certain naturally occurring minerals (e.g., ocher and Prussian blue ). They have been almost entirely replaced in modern dyeing by synthetic dyes. Most of these are prepared from coal tar, being formed from an aromatic hydrocarbon such as benzene, from which indigo is derived (see also aniline ), or anthracene, which yields alizarin. Although some materials, e.g., silk and wool, can be colored simply by being dipped in the dye (the dyes so used are consequently called direct dyes), others, including cotton, commonly require the use of a mordant (see also lake ). Alizarin is a mordant dye and the color it gives depends upon the mordant used. Dyes are classified also as acidic or basic according to the medium required in the dyeing process. A vat dye, e.g., indigo, is so called from the method of its application; it is first treated chemically so that it becomes soluble and is then used for coloring materials bathed in a vat. When the materials become impregnated with the dye, they are removed and dried in air, the indigo reverting to its original, insoluble form. The process by which a dye becomes "attached" to the material it colors is not definitely known. One...
