Pas·tel n.
 1. A crayon made of a paste composed of a color ground with gum water. [Sometimes incorrectly written pastil.]  “Charming heads in pastel.”
 2. Bot. A plant affording a blue dye; the woad (Isatis tinctoria); also, the dye itself.

 ◄ ►


 Woad n.  [Written also wad, and wade.]
 1. Bot. An herbaceous cruciferous plant (Isatis tinctoria) of the family Cruciferae (syn. Brassicaceae). It was formerly cultivated for the blue coloring matter derived from its leaves.  See isatin.
 2. A blue dyestuff, or coloring matter, consisting of the powdered and fermented leaves of the Isatis tinctoria. It is now superseded by indigo, but is somewhat used with indigo as a ferment in dyeing.
    Their bodies . . . painted with woad in sundry figures.   --Milton.
 Wild woad Bot., the weld (Reseda luteola).  See Weld.
 Woad mill, a mill grinding and preparing woad.

 ◄ ►


 In·di·can n.
 1. Chem. A glucoside (C14H17NO6) obtained from woad (indigo plant, Isatis Tinctoria) and other plants (see indigo), as a yellow or light brown sirup. When purified it is obtained as spear-shaped crystals.  It has a nauseous bitter taste.  By the action of acids, enzymes, etc., it breaks down into sugar and indigo. It is the source of natural indigo.   Chemically it is the 3-glucoside of indole, H-indol-3-yl-β-D-glucopyranoside.
 2. Physiol. Chem. An indigo-forming substance, found in urine, and other animal fluids, and convertible into red and blue indigo (urrhodin and uroglaucin). Chemically, it is indoxyl sulphate of potash, C8H6NSO4K, and is derived from the indol formed in the alimentary canal. Called also uroxanthin.

 ◄ ►


 In·di·go n.; pl. Indigoes
 1. A kind of deep blue, one of the seven prismatic colors.
 2. Chem. A blue dyestuff obtained from several plants belonging to very different genera and orders, such as, the woad, Isatis tinctoria (family Cruciferae), Indigofera suffroticosa, Indigofera tinctoria (family Leguminosae), Indigofera Anil, Nereum tinctorium, Polygonum tinctorium Ait. (family Polygonaceae), etc.; called also natural indigo.  It is a dark blue earthy substance, tasteless and odorless, with a copper-violet luster when rubbed.  Indigo does not exist in the plants as such, but is obtained by decomposition of the glycoside indican.
 Note: ☞ Commercial indigo contains the essential coloring principle indigo blue or indigotine, with several other dyes; as, indigo red, indigo brown, etc., and various impurities. Indigo is insoluble in ordinary reagents, with the exception of strong sulphuric acid.
 Chinese indigo Bot., Isatis indigotica, a kind of woad.
 Wild indigo Bot., the American herb Baptisia tinctoria which yields a poor quality of indigo, as do several other species of the same genus.


 I·sa·tis n.  Bot. A genus of herbs, some species of which, especially the Isatis tinctoria, yield a blue dye similar to indigo; woad.

 ◄ ►


 Isatis tinctoria
      n : European biennial formerly grown for the blue coloring
          matter yielded by its leaves [syn: dyer's woad]