Page:De Vinne, Invention of Printing (1876).djvu/317

Rh some pages the slipping or displacement of this paper mask caused the false letters to be printed in black; on one other page the mask slipped so trivially that one-half of the false types was printed in black, while the other half was embossed in white on another page the mask slipped over the text type, and obscured the end of the line. These were exceptional errors; the general execution of this part of the work shows that the printer was a man of some intelligence, and that with imperfect materials he performed a very difficult task.

Invention of Printing p307.jpg The operation of presswork begins with inking the form on the bed of the press, which, in this illustration, is supposed to contain a form not unlike that of the Speculum, nested in a chase type-high. The sheet is laid on the tympan against guides that keep it in place. The frisket, containing the paper masks cut out to sink the irregularities of the form, is folded down in the line A B, partially covering the paper on the tympan. The tympan is then folded over on the line C D, which operation brings the paper down on the face of the form, ready to receive the impression. These are the appliances of a modern press. The frisket of the unknown printer was of much simpler construction, probably nothing more than a mask of paper laid on the form of types by hand.