Before the dawn of history man had learned how to decorate the surface of his fabrics with colors. The primitive South Sea Islander applies color to his bark cloth by dipping a fern leaf into his dye made from bark, berries, or colored earths, and laying the leaf on the cloth. Higher up in the development of industries comes the use of a stencil, wonderfully developed by the Japanese. A block of wood with a design engraved upon it, which was dipped in the paint and then applied to the cloth, was an early method of printing. With the development of machinery came the copper roll with the design engraved upon it, this giving a continuous application of the pattern, whereas the block print must be applied separately for each repeat of the pattern. At the present time both the wooden block and the copper roll are used, although for general commercial purposes the block has almost disappeared.
Fig. 32. Block for Printing.
The purpose of printing, as opposed to dyeing, is to produce upon the cloth a design in one or many colors without the complicated weave that would be necessary if it were produced with threads dyed in the yarn. The effect obtained is also very different from the effect of a woven design. In organdies and thin materials it would not be possible to produce the delicate color effects in any other way except by hand painting.
Printing may be done on woven cloth or on the warp threads before weaving. The latter method produces a somewhat indefinite or soft effect, very attractive in Persian silks, Dresden ribbons, and other materials. This method is used also in tapestry rugs, where economy of material is desired. In this case, however, the result is not particularly good.
The machinery used for printing consists of a large drum with an endless blanket, over which the cloth passes slowly, and copper rolls, one for each color in the design, revolving in close contact with the cylinder. The part of the pattern to be produced in any one color is engraved on its particular roll; therefore in very elaborate designs there may be as many as twenty rolls. The colors for printing are mixed, thickened with gum, and put into troughs just below the copper rolls. A feed roll covered with felt dips into the dye and comes against the copper roll, supplying it with color. A strip of steel called a "doctor" scrapes all the dye off the copper roll, except that which is in the engraved parts; this goes onto the cloth, and there must be just enough to print the pattern, but not enough to run. Since the large drum is heated the dye is almost immediately dried.
There are three methods of producing a printed design on a cloth. The first or direct method is given above, and is used mostly for cloth with a white background. For cloth which is to have a colored background with the figure printed upon it, other methods are used. In the discharge method the cloth is first dyed a solid color; the design is then printed on with some chemical which removes the color from the spot which is to furnish the design.
The resist method consists in printing the design on the cloth with a chemical which prevents the absorption of the dyestuff, and thus, when the cloth is dyed later, the design is left white or of the desired color. A great variety of effects may be produced with the discharge and resist methods of printing. The greatest difficulty with them is that frequently the chemical used is too strong and weakens the cloth, especially if it is not entirely removed. Sometimes in cheap prints the figure will drop out entirely, long before the main body of the cloth is worn out.
Careful mixing of color and thickening agent, of color and mordant, or proper mordanting of the cloth before printing is very essential. The color is usually developed after printing by steaming or by treating with a chemical developer. Care must be taken that the machinery is adjusted exactly; otherwise too little or too much color may be applied.
When printing warps, the threads must have been previously wound on the warp beam as they are to go into the loom, and this relative position must be kept.
The possibilities of machine printing are numerous, and the results may be beautiful or hideous according to the taste of the designer and the choice of colors.
Block printing is still used by craft workers and in the manufacture of expensive chintz, cretonne, silks, etc., where the design is very elaborate and a particularly artistic effect is desired. Block printing has a more individual appearance than machine printing. The Japanese are past masters in the art of block printing, as they are in stenciling, their prints on paper being most wonderful.
Fig. 33. Cotton Prints.
A. Japanese Print B and C. French Chintz printed on warp before weaving.
Liberty & Company, London and Paris, produce beautiful block-printed silks, satins, and cottons at their print works in Merton Abbey, England, where are also located the print works started by William Morris, in which blocks only are used.
Fraps, G. S. Principles of Dyeing.
Knecht, E., Rawson, G., and Loewenthal, R. A Manual of Dyeing.
Matthews, J. M. Laboratory Guide of Dyeing and Textile Chemistry.