The printing of the patterns upon the cloth may be carried out in various ways, the earliest method being by means of wooden blocks, on which the figures of the patterns stood out in relief. Where several colors were employed in one pattern, a block for each color was neces sary. In a set of blocks for one pattern, each block, although at first having the same design drawn upon it, was cut in such a manner that it ultimately transferred only a single color, which appeared in different parts of the pat tern. When all the blocks had been applied, the various colors printed completed the origi nal design. To ensure accurate juxtaposition of the colors, each block was furnished with brass points at the corners, in order to guide the workman. The printer first furnished the face of the block with the requisite color by pressing it several times on a piece of woolen cloth suitably stretched and supported on a so called color-sieve, and which had been previ ously brushed over with color by a boy attend ant. The printer then applied the block to the surface of the calico, which was stretched on a long table covered with felt, striking the back of the block with his hand or with a small mal let. The operation of block printing was slow and tedious and though many improvements have been introduced, and tt can even be effected by mechanical power, as in the so called Perrotine machine, it is now only em ployed to a very limited extent for certain special kinds of work: Another mode of print ing, introduced about 1760, is by means of en graved copper-plates, but its employment is also similarly restricted.
The modern method of printing, which dates from 1785, is effected by means of engraved copper cylinders, and this method has now practically superseded all others.
The method of engraving employed varies according to the kind of pattern to be put on the roller. In the case of very large patterns the figures are engraved by hand on the cylin ders themselves with the use of the ordinary tools of the copper-plate engraver. For smaller designs, however, which are often repeated, it is usual in the first instance to engrave the tern by hand on a very small cylinder of soft steel in intaglio, just as it will ultimately ap pear on the copper. This steel cylinder, which is called a die, is then tempered to a high degree of •hardness, and by means of machinery is pressed against another cylinder of soft steel, on which the pattern is thus made to appear in relief. This last cylinder, called the mill, is then hardened, and, being pressed against the copper cylinder, the figures are indented and the roller is ready for use. In the first instance the original pattern of the designer has always to be reduced or enlarged, so as to repeat an exact number of times over the roller to be engraved. In order to reduce the amount of skilled labor one repeat only of the pattern is engraved on the die; the mill, which is of larger diameter, has two, three or four repeats; while the num ber of repeats on the circumference of the cop per cylinder is still greater. A third method of
engraving,. which has now largely superseded the foregoing, is that of etching, in conjunction with the pantograph system of transferring the design to the copper roller. The roller, being coated uniformly with a bituminous varnish, has the pattern traced on the varnish in the pentagraph machine by a set of diamond points, and it is then submitted for a very brief period to the action of nitric acid. In the parts where the pattern has been traced the varnish is re moved, there the copper is speedily attacked by the acid, and the pattern is thus etched upon it. After removing the varnish the roller is ready for printing.
The cylinder printing machine consists of a large central iron drum, around which are ar ranged one or more engraved copper rollers, according to the number of colors to be printed simultaneously. Each roller is provided with the means of making several adjustments, in order to determine the exact position of the color which it prints. The central drum is wrapped with cloth, and it is further provided with an endless blanket and back-cloth, so as to present a yielding surface to the printing rollers. The cloth to be printed passes from a roll behind the machine, round the central drum in a tightly stretched condition, while the sev eral printing rollers press forcibly against it. Each roller, as it revolves, is fed with color from a small trough below, the superfluous color being scraped off the plain surface of the roller by means of a sharp-edged steel blade, or °doe tor,x' thus leaving the color only in the en graved portions. As the rollers thus charged with color press against the cloth, the latter absorbs or withdraws the color from the en graving, and the pattern is thus transferred to the calico. By this machine as much work can be performed in three minutes as could be done by block printingin six hours. After the cloth has received the impression from the rollers it passes over a series of steam-heated flat irons, chests or cylinders, and is thus dried.
In close connection with the printing machine department is the so-called color house or color-shop, where the solutions of coloring matters are suitably thickened and made ready for the printer. The color-house is provided with numerous steam-heated cop per pans, so arranged on supports that they can be readily turned over for emptying or clean ing. The color mixtures are stirred with wooden blades by hand, or by mechanical agita tors, and carefully strained through cloth be fore use. The thickening of the color solutions with starch, flour, gum, dextrine, albumen, etc., is necessary to prevent the spreading of the color by capillary attraction beyond the printed parts, and thus ensure sharp and neat impres sions. Near the color-house is a chemical laboratory, and a drug room containing the store of coloring matters, dyewood, extracts, thickenings, chemicals, etc.