Roller printing on textiles
[1] Improvements in the technology resulted in more elaborate roller prints in bright, rich colours from the 1820s; Turkey red and chrome yellow were particularly popular.
The cast iron pressure cylinder is wrapped with several thicknesses of a special material made of wool and cotton lapping, the object of which is to provide the elasticity necessary to enable it to properly force the cloth to be printed into the lines of engraving.
On the perfect action of this doctor depends the entire success of printing, and as its sharpness and angle of inclination to the copper roller varies with the styles of work in hand it requires an expert to get it up (sharpen it) properly and considerable practical experience to know exactly what qualities it should possess in any given case.
In order to prevent it from wearing irregularly it is given a to-and-fro motion so that it is constantly changing its position and is never in contact with one part of the engraving for more than of brass or a similar alloy is frequently added on the opposite side of the roller to that occupied by the steel or cleaning doctor; it is known technically as the lint doctor from its purpose of cleaning off loose filaments or lint, which the roller picks off the cloth during the printing operation.
[9] Larger machines printing from two to sixteen colours are precisely similar in principle to the above, but differ somewhat in detail and are naturally more complex and difficult to operate.
Notwithstanding the great latitude of movement thus provided each roller is furnished with a box-wheel, which serves the double purpose of connecting or gearing it to the driving wheel, and of affording a fine adjustment.
; and thirdly, the wonderful exactitude with which each portion of an elaborate multicolour pattern can be fitted into its proper place, and the entire absence of faulty joints at its points of repeat or repetition consideration of the utmost importance in fine delicate work, where such a blur would utterly destroy the effect.
[5] The engraving of copper rollers is one of the most important branches of textile printing and on its perfection of execution depends, in great measure, the ultimate success of the designs.
The design is transferred to the roller from an oil colour tracing and then merely cut out with a steel graver, prismatic in section, and sharpened to a beveled point.
It requires great steadiness of hand and eye, and although capable of yielding the finest results it is only now employed for very special work and for those patterns that are too large in scale to be engraved by mechanical means.
The necessity for this is that in subsequent operations the design has to be again reduced to its original size and, if the outlines on the zinc plate were too small at first, they would be impracticable either to etch or print.
It is then repolished, painted with a chalky mixture to prevent its surface oxidizing and exposed to a red-heat in a box filled with chalk and charcoal; then it is plunged in cold water to harden it and finally tempered to the proper degree of toughness.
[11] The copper roller must in like manner have a circumference equal to an exact multiple of that of the mill, so that the pattern will join up perfectly without the slightest break in line.
The mill is placed in contact with one end of the copper roller, and being mounted on a lever support as much pressure as required can be put upon it by adding weights.
