Before it is printed the cloth is subjected to various preliminary processes, depending upon the nature of the fabric. Cotton goods are bleached and padded or treated to dressing to give them the proper body and surface. They are then run through the lint-doctor to remove all hairy projections. Woolen goods must be treated to a preliminary bath in a weak solu tion of sodium hypochlorite. The cloth is moist ened before printing, and after printing is washed and dried. Silk has to be prepared for printing by suitable agents. such as tin with or without an acid. Both wool and silk require to be entirely freed from grease before they can be printed.
The preparation of the colors for printing re quires great skill and knowledge of the proper ties of the different dyestuffs. The colors are mixed in copper pans so mounted that their contents can be boiled by steam, cooled with water, and easily emptied. Wooden paddles are provided for stirring the colors, or the agitation may be performed by mechanical appliances. As most of the colors are thickened with starch or flour. so that they will spread well, they re quire straining through a copper wire sieve.
The printing of cotton fabrics is a much more complicated and difficult process than that of printing silk or wool, because many of the com plex methods that may be applied to the former are, from the nature of the material, inappli cable to the latter. The many different methods and combinations of methods by which the color affects are produced on cotton fabrics have been variously classified by writers on textile print ing. To understand the production of these different so-called 'styles' involves a knowl edge of the principles and chemistry of dyeing. (See DYEING.) The simplest classification is that adopted by Georgievic, in his work named in the bibliography. According to his classifica tion, the production of a pattern upon cot ton cloth may be accomplished as follows: (1) Direct printing; (2) combined dyeing and printing; (3) discharge style printing; (4) re serve style printing. Direct printing is done by mixing the desired color with the proper fixing agents and applying the mixture directly to the fabric. In combined dyeing and printing, the printing is clone with mordants, and then the whole fabric is dyed. In the discha-rgc style the effect is produced either by using a solution that will discharge the mordant or the dye itself. In the reserrc style various substances, printed on the fabric, are employed to prevent absorp tion or development of other colors subsequently applied by padding or dyeing. The last three groups belong to the general class of dyes, as opposed to simple printed colors.
Considering these four groups more carefully, we find that in direct printing three general methods are used for fixing the color upon the fabric. the method used in a given case depend ing upon the chemical nature of the dyestuff.
These methods are: (1) Steaming, in which printing is followed by air drying and steaming, or by immediate steaming, drying, and again steaming; (2) oxidizing, in which the color is fixed by the process known as 'aging,' either by prolonged exposure to the air or by passing through a steam `alter;' (3) reducing, a method applied to indigo printing. Indigo is printed upon fabrics in two ways known as the 'gin and 'reduced indigo' processes which are briefly described by Sadtler (see bibliography) as follows: By the first. method "Indigo is fine
ly ground and made into a paste with water, to which is added caustic soda ; this is now kept in a. closed Tes...el in order to prevent as much as possible the absorption of carbonic acid from the atmosphere. The proportioning of the in gredients depends on the desired shade of blue. When used in printing it is thickened with dex trin and starch. . . The cloth, before ing printed upon, is worked through a twenty five per cent. solution of glucose and dried. After printing, the cloth must be again dried and passed through an atmosphere of wet steam, to effect the reduction of the indigo which now takes place. The cloth is now washed in water, being repeatedly. during the washing, exposed to the air, when the reduced indigo is oxidized and its real color appears. . . The second process is based upon the fact that indigo, when finely ground and mixed with lime and thiosul phate of soda in suitable thickening agents, is reduced; if with this reduced indigo paste, pat terns are printed upon cotton fabrics, and then exposed to the air, the indigo is oxidized with a regeneration of the blue color. The pieces are then washed and dried. Instead of using in digo in printing. one of the newer colors, im 'medial blue, is now very extensively used and printed with suitable mordants directly upon the goods." Passing on to the second general method of textile printing, which is a combination of print ing and dyeing, four operations are involved. First, the fabric is printed with the appropriate mordant ; then follows the a-ging process, dur ing which the printed mordant is decomposed and more firmly fixed to the cloth: then follows an operation known as (lunging, which removes the thickening, no longer needed in the mordant ; and finally dyeing, the dye, of course, remain ing fixed only to that part of the fabric which was previously treated with the mordant. The aging process was formerly conducted in large chambers and consumed several weeks. It is now performed in steam `alters,' much more rapidly; hut cloth that is rapidly aged does not hold its color as well as when the operation is conducted more slowly. Dunging is a passing of the cloth through solutions of sodium phos phate, arseniate, or silicate, these chemicals being now employed in place of the somewhat offensive cow-dung. The composition of the dye bath is described under DYEING..
For the third, or discharge style of printing, the discharges are simply substances printed upon the goods, the whole of which has been mordanted, so that the mordant is removed front the printed spots, and when the goods are finally dyed the printed figures will be white, while the background will be the color naturally produced by the dye and mordant.
ln the fourth, or reserve, style of printing, substances are printed upon the fabric which will prevent the fixation of color in those places. Reserves are of two general kinds: chemical, such as citric acid. and mechanical, such as pipe clay, beeswax, or other inert substance.
These four general methods of textile print ing, briefly outlined above, are susceptible of end less modification and combination. Rothwell (see bibliography) gives ten possible methods which lie groups under seven 'styles.' llany of them are applicable only to cotton.