272 



DYES AND DYEING 



DYES AND DYEING 



importance are produced by processes which con- 

 sist essentially in manufacturing the dye in an 

 insoluble form in the goods. 



Calico^inting. 



Calico-printing may be considered as local dye- 

 ing. It is the art of producing on woven material 

 a design in color by certain processes, one of which 



Fig. 378. Woad (Isatie tinctoria). a, Lower leaf; t, first year 

 leaf; c, mature fruit. Source of a blue dye. 



is a printing process. The art has been developed 

 from the early painting of cloth in India (in Cali- 

 cut, hence the name " calico ") to the modern print. 

 There is probably no other industry in which so 

 great a combination of artistic, mechanical, chem- 

 ical and technical skill of the highest order is 

 required, and this, too, to produce so cheap a 

 finished product. Formerly the prints were made 

 from wooden blocks cut in relief, there being a set 

 of blocks equal in number to the colors desired if 

 the pattern were small, or, if large, as many for 

 each color as were necessary to make the complete 

 design. This process is known as block printing 

 and is done by hand. For large designs, or for 

 those of more than twenty colors, this method is 

 employed today and to a considerable extent to 

 meet the demand for more artistic goods. The 



Japanese produce some very beautiful goods by ap- 

 plying the colors with stencils. This method can 

 be used by any one, and very artistic effects can be 

 produced at a trifling expense. In fact, this work 

 should prove most interesting to amateurs, as most 

 elaborate designs may be made. 



The modern calico-printing machine consists of 

 a large iron cylinder about which copper rollers 

 are mounted. The cylinder is padded and the 

 design is engraved in the copper rollers, each roller 

 being engraved to apply one color ; as many rollers 

 are necessary as there are colors in the pattern. 

 Beneath each roller is a trough or "color-box" 

 from which the color is carried to the roller by a 

 wooden roller covered with cloth, or by a cylindri- 

 cal brush. The entire surface of the copper be- 

 comes coated with the color, but as it revolves, a 

 sharp blade, known as the " doctor," scrapes off all 

 the color except that in the engraved part. The 

 cloth to be printed passes between the large cylin- 

 der and the copper rollers, and the color is trans- 

 ferred to it. With one passage the entire design is 

 produced. In order to give it a resilient surface, an 

 endless web, called the blanket, also passes through, 

 and between it and the cloth to be printed un- 

 bleached cloth passes, which serves to take up the 

 surplus color. A second "doctor," called the lint 

 doctor, removes any loose fibers from the copper 

 roller.. The rollers are so mounted in the framework 

 that they may be adjusted while the machine is in 

 operation, so that any misfit can be corrected. As 

 the cloth passes from the machine it is dried and 

 given such other treatment as the style of work 

 may require. 



Pigments are printed by being mixed with blood 

 albumen, or the white of egg, for delicate shades. 

 On steaming the printed goods, the albumen is 

 coagulated, becomes insoluble and fixes the color. 

 Basic colors are mixed with tannin and acetic acid, 

 in which the tannin lake of the color is soluble ; in 

 drying, the acetic acid evaporates and the insoluble 

 lake is produced. Mordant colors are similarly 

 applied. 



Another process consists in printing on the thick- 

 ened mordants and then dyeing the goods. The 

 color is fixed where the mordant has been printed. 



Patterns are produced by printing dyed goods 

 with chemicals which destroy the color. This is 

 known as discharge work. Starches, gums, flour 

 and other similar bodies are used in making the 

 printing pastes. Wool, silk and yarns are also 

 printed; the latter, however, on a machine in which 

 the design is in relief. Both sides of the cloth may 

 be printed in one passage through a double machine. 

 If the patterns on both sides are to be alike and 

 are required to fit properly, it is necessary to 

 have the sets of rollers engraved in pairs, and in 

 reverse order. 



Home dyeing. 



In all dyeing processes it is essential to have 

 the goods free from grease, dirt and foreign mat- 

 ter, and, for light colors, they should be bleached. 

 In home dyeing, strict attention should be paid to 

 cleanliness of the goods, and care taken accurately 



