INTAGLIO PRINTING Any method of printing in which the lines, dots, grain, or other elements of the engraving are sunk in the plate, so that the depressions are filled with ink for printing, as distinguished from relief plates or blocks where the printing elements are raised and are inked on their sur faces. Thus the old engraving or etching pro cesses, such as mezzotint, aquatint, needle point etching, copper and steel plate engraving, and the like are intaglio printing processes. Photogravure and heliogravure are also intaglio methods. Of late, the term intaglio printing has come to be applied in a more limited sense to methods of forming a sunk engraving or etching by means of a ruled screen, and the printing of the same by mechanical power. For some years past there have been machines for printing from flat plates, the sunk image being inked and the surface being wiped clean by mechanical arrange ments. Such machines have, however, not come into general use, there being almost insuperable difficulties in efficiently wiping the flat surface. Rotary intaglio printing solves this problem very successfully, and the method has been success fully worked for some years by a Lancaster firm which was the first to carry out the experiments and devise suitable machinery for this work. Their methods are secret, but a number of later experimenters have proceeded on the assumption that a photographic carbon print, which has been also exposed under a ruled screen, is devel oped on a hollow copper cylinder. The carbon print forms a resist as in the photogravure pro cess, and the image is thereby etched in intaglio.
The spaces between the screen lines form minute cells which hold the ink, preventing its being wiped out during the printing operation. The hollow cylinder is placed on a mandrel and mounted in a machine similar to that which is used for wallpaper or calico printing. Under the engraved cylinder is an inking roller working in a trough of thin ink, and feeding the ink into the engraving. Above the engraved cylinder is an impression roller with an elastic covering of blanket or rubber. In contact with the engraved cylinder is a steel knife, called the " doctor," which scrapes the surplus ink quite cleanly from the surface, leaving it in the hollows of the engraving. Paper is fed from a reel, and passes between the impression cylinder and the engraved cylinder, thus receiving a print at every revolu tion of the latter. Mechanism is provided for delivering and cutting off the prints. The method has been found to present considerable difficulties.
Dr. E. Mertens, of Freiburg, has extended the process to newspaper printing by coupling up the intaglio machine to the ordinary rotary stereo printing machines, so that when the web of paper emerges from the intaglio printing machine it passes into the newspaper rotary to receive the impression of the text formes.
The rotary intaglio method has been applied to colour printing with very fine results.