Sumac (Sicilian): Rhos Coriaria. Alum lake, olive.
Sumac (Virginian): Rhus hirta. This and the above are used in dyeing processes as a source of tannin.
Tyrian purple : Murex, Purpura, Bucciniurn, etc. (sea shells). The purple dye of the Phmnicians, Greeks and Romans.
Turmeric, or curcuma, Indian saffron, terra merits, souchet, safran d' Inde : Curcuma longa, C rotunda. Yellow.
Ventilago Madras-patana, or oural patti, pitti, lokandi, kanwait, etc. : Ventilago Madraspatana. Lakes, blue.
Virginia creeper : Parthenocissus (or Aeopelopsis) quinquefolia. Red color.
Waifs, or hoai-hoa, Chinese yellow berries : Sophora Japonica. Alumina lake, yellow.
Wallflower : Cheiranthus Clteiri. Yellow lakes pre pared from the blossoms.
Wall lichen : Parmelia parietina. Yellow.
Warns : Moghania congesta (Flemingia congesta). Red resinous powder.
Weld, or wau, gaude, yellow weed, dyer's rocket : ResedaLuteo/a. (Fig. 377). Alumina lake, yellow. With chromium, olive-yellow ; with tin, bright yellow ; with iron, olive. Considered superior to all other natural yellow color ing matters, but now displaced by several synthetic dye stuffs.
Whitethorn, or blackthorn : Cratesgus oxyacantha. Yellow lakes from blossoms.
Woad, or pastel, waid : Isatis tinctoria, L Lusitanica. (Fig. 378). Contains indigo. Formerly cultivated in Eng land and Holland.
Mineral coloring matters.
Of the many inorganic coloring matters, only chrome yellow, chrome orange, iron and manga nese oxids and Prussian blue may be treated under dyestuffs. None of these is used as such, hut they are produced on textiles by chemical reactions The goods are first treated with a solution of one of the chemicals, and then on working in another solution the pigment is produced. In calico-print ing, any pigment can be fastened mechanically as in ordinary printing, except that gum arabic, dex Fig. 376. Saffron (Crocus sativus). Source of a yellow dye.
trin, starch, albumen, and the like, are employed instead of varnishes.
Definitions.
Lakes are insoluble compounds of alumina and coloring matters. If these are formed by them
selves, a color-lake or pigment is produced ; but if a fabric is first impregnated with alum or other metallic salts for which the fiber has an affinity, on subsequent treatment in the coloring solution the color-lake is produced in and on the fiber, which is then said to be dyed. Several other metallic oxids also possess similar properties, often giving differ ent colored precipitates with the same dyestuffs. These metallic compounds are called "mordants" (from the French mordre, to bite). Tannic acid forms insoluble compounds with an entire series of coloring matters and is similarly used.
Although dyeing has been practiced from time immemorial, and by all nations of the globe, no satisfactory theory has been advanced to explain the process. Mechanical attraction, chemical affin ity and "solid solution" are given as explanations, all having experimental evidence in support. In wool dyeing, the chemical affinity theory 'best elucidates the process.
Classification of dyestuffs.
The dyestuffs may be classified either according to their chemical composition, in accordance with the fibers for which they are most suitable, or with the methods used in their application. The first classification is of importance to the chemist, while the last is best for practical purposes, and is shown in the following grouping ; (a) Direct cotton colors. These dye cotton in full shades without the aid of mordants ; in conjunction with them, certain salts, such as glauber salt or common salt, are used to aid in the absorption of the dye, as these salts tend to force it out of the solution. Alkaline salts, such as soda, soap or phosphate of soda, have an opposite effect and tend to retard the dyeing process and to prevent uneven dyeing. The direct cotton colors also act as mordants, combining with the colors of the following class. These dyes may be converted into others by treat ment with certain chemicals, thus making a new dye on the goods.