DYERS' GREENWEED 2747 



Dyers' Greenweed OR WOAD- extends into N. and W. Asia. The 

 WAXEN (Genista tinctoria). Dwarf bright yellow flowers are small, 

 shrub of the natural order Legu- and are succeeded by smooth, flat 

 minosae. A native of Europe, it pods, an inch long, containing about 



five seeds. It yields a yellow dye, 

 which was largely used by dyers in 

 connexion with natural indigo. 



Dyers' Oak (Quercus velutina). 

 Large tree of the natural order 

 Amentaoeae. A native of N. 

 America, it is ^ 

 known as quer- ' 

 citron and yel- 

 low-barked 

 oak, the rough, 



brown bark jjS|| / 



being orange- 

 coloured in- i 

 ternally. It has 

 variously di- \ 

 vided large j 

 leaves and t ...... 



small he mi- Dyers' Oak, leaf and 

 spherical acorn 



acorns. The bark is extensively used 

 in tanning and dyeing. 



DYES AND DYEING : A KEY INDUSTRY 



Mark Meredith, Editor of The Indian Textile Journal 



This article classifies the various kinds of dyes and describes the 



materials of which they are made. See the articles on materials 



which are dyed, e.g. Cotton. See also Perkin and other chemists 



Dyers' Greenweed, Sowers and 

 fodage 



Dyes or dyestuffs are sub- 

 stances used for dyeing the various 

 textile fibres, as wool, silk, cotton, 

 artificial silk ; also for dyeing 

 leather, paper, etc., and for colour- 

 ing oils, varnishes, foodstuffs. 



Chemically, dyestuffs are of very 

 diverse character, and with a few 

 exceptions (mineral dyes- tuffs) are 

 composed of carbon and hydrogen, 

 associated with one or more of 

 o'. her elements, as oxygen, nitrogen, 

 sulphur, chlorine, bromine, iodine, 

 and sometimes with the metals 

 sodium, potassium, or calcium. 



Mineral dyestuffs comprise Prus- 

 sian blue, iron buff, chrome yellow, 

 chrome orange, manganese bronze, 

 and metallic oxide khaki. They 

 are chiefly used for cotton, but 

 have lost their former importance. 

 They are produced by depositing 

 coloured salts of metals within the 

 fibre, i.e. cotton cloth is impreg- 

 nated with a soluble salt of a 

 metal, squeezed, and then treated 

 with another solution so that an 

 insoluble metallic compound is 

 formed and firmly fixed on the 

 fibre. The mineral dyestuffs are 

 very fast to light and washing, 

 except that Prussian blue is turned 

 brown by alkalis. Metallic oxide 

 khaki, produced from salts of iron 

 and chromium, was largely used 

 during the Great War. 



NATURAL DYESTUFFS. Dyestuffs 

 may be divided into (1) natural 

 and (2) artificial. The first class 

 comprises the vegetable dyentuffs, 

 logwood, etc., also cochineal and lac 



dye, the two latter being produced 

 from an insect. The f am ous Ty rian 

 purple of history came from certain 

 molluscs. 



The most important natural dye- 

 stuffs are natural indigo, logwood, 

 fustic, cochineal, Persian berries, 

 orchil, cudbear, and cutch. Of 

 lesser importance are barwood, 

 Brazilwood, camwood, Sanders- 

 wood, and weld. In 1914 only the 

 members of the first group were 

 used to any great extent, and the 

 consumption of these (especially 

 natural indigo) was gradually de- 

 clining. 



During the Great War all 

 natural dyestuffs again became 

 more prominent, owing to the 

 great shortage of artificial colours, 

 and in 1920 the demand for log- 

 wood and orchil was greater than 

 the supply. Mention should be 

 made here of " madder," formerly 

 much used for madder reds, but 

 the colouring principle of this 

 vegetable dyestuff, alizarin, is now 

 produced artificially, and the 

 natural product is only used in 

 very small quantities for use in 

 indigo vats. The chief sources of 

 the natural dyestuffs are the W. 

 Indian Islands, India, S. America, 

 and S. Europe. 



Natural Dyestuffs 



With the exception of indigo and 

 orchil, the natural dyestuffs are 

 those which, applied alone to 

 the textile fibres, possess little 

 affinity for them, and are only of 

 use when combined with metals, 



DYES 



previously applied to the fibres in 

 the form of salts. They are, more- j 

 over, polygenetic in character, 

 i.e. they produce different shades 

 according to the metallic salt 

 (chrome, aluminium, tin, or iron) 

 previously applied to the fibre, 

 this latter operation being techni- 

 cally called " mordanting." Hence 

 the natural dyestuffs are called 

 mordant colours, in distinction to 

 the classes in the artificial dye- 

 stuffs, such as acid, basic salt, etc. 

 Indigo and Logwood 



Natural indigo is marketed in 

 lumps, varying in strength, and 

 must be ground before use in the 

 indigo vat. It belongs to the series 

 of vat colours, and is one of the 

 oldest dyestuffs. Logwood is used 

 in the form of rasped wood, log- 

 wood extract, and haematein 

 crystals. Haematein crystals con- 

 tain the actual colouring principle 

 haematein, and are the most con- 

 centrated form of dyestuff. Log- 

 wood is used in conjunction with 

 fustic, chiefly for blacks on wool 

 and silk, and is noted for its fine 

 bloomy shade, which is difficult to 

 reproduce with artificial colours. 

 Cochineal dyed on a tin and alu- 

 minium mordant was formerly 

 used for scarlet. Cutch is mostly 

 employed on cotton, giving very 

 fast browns. 



ARTIFICIAL DYESTUFFS. These are 

 commonly called coal tar dyes. The 

 first artificial dyestuff was dis- 

 covered by Perkin in 1856 and 

 called mauve. Since that date 

 some thousands of dyestuffs have 

 been put on the market by different 

 makers, but these do not all repre- 

 sent individual colours, as the same 

 dyestuff occurs under many dif- 

 ferent names, and many also are 

 mixtures. 



Dyestuffs from Coal Tar 



The artificial dyestuffs comprise 

 a very large number of organic 

 compounds, varying in compo- 

 sition from a simple derivative, 

 such as picric acid, to a very com- 

 plicated one, as indanthrene dark 

 blue. Chemically, they are divided 

 into about 15 classes, the dye- 

 stuffs in each conforming to a defi- 

 nite structure ; but dyestuffs from 

 different classes may behave alike 

 from a dyeing point of view, and 

 taking the latter as a basis for 

 differentiation, the following classes 

 of dyestuffs are obtained : (1) acid, 

 (2) basic, (3) direct cotton or salt 

 colours, (4) mordant, (5) sulphide, 

 (6) vat, (7) insoluble colours or 

 colours formed on the fibre. 



As the name indicates, the dye- 

 stuffs of this group are derived from 

 coal tar. From this are obtained 

 by various processes of distillation 

 and purification such important 

 substances as benzene, toluene, 



