Page:De Vinne, Invention of Printing (1876).djvu/35

 Rh Typography has a marked advantage in the greater ease with which printing types are inked. In the copper-plate process, the plate must be first blackened over the entire surface, and then cleansed with even greater care, before an impression can be taken. This labor cannot be intrusted to machinery, but must be done by a practised workman. The inking of a lithographic stone is as difficult: the stone must be moistened before the inking roller can be applied. This double operation of inking and cleansing, or of inking and moistening, is required for every impression. The inking of types is done by a much simpler method; one passage, to and fro, of a gang of rollers over the surface is sufficient to coat them with ink. The types need no previous nor after application.

The impression by which typographic surfaces are printed is comparatively slight. The sunken lines of a copper plate or the transferred lines of a lithographic stone can be reproduced on paper only by means of violent impression, which is obtained by forcing the plate or the stone under an iron cylinder or scraper. Only a part of the surface is printed, but the entire surface must receive impression, which is, of necessity, gradually applied. A direct vertical pressure, at the same instant, over every part of the surface, would crush the stone or flatten the plate. In printing types of ordinary form, the area of impression surface is exactly the reverse of that of the lithographic stone or the copper plate. It is only the part which is printed that receives the ink and the