All the materials for presswork were imperfect The types, cut to length by a saw, were of uneven height; the paper was usually of very rough surface and of irregular thickness; the platen of wood, rarely ever truly flat, must have given unequal pressure at different corners. It was necessary that some substance should be put between the platen and the white sheet which would compensate for these irregularities. 
Early inking Balls.
[From a Playing Card of Sixteenth Century.]This substance was a woolen blanket, in two or more thicknesses, which spread or diffused the impression. The wetting of the paper, which made it soft and pliable, materially aided the pressman, but his great reliance seems to have been on strong impression. All the old cuts of presses represent the pressman tugging at the bar with a force which seems out of all proportion to the size of the form.
The early press was rude, and the method of printing was unscientific, but in many offices the pressman. was superior to his press and his method. By doing his work slowly and carefully he often did it admirably. It was always done slowly, with a waste of time which, if allowed in the modern practice of printing, would make books of excessive price. Some notion of this waste may be had after an examination of the letters of the Psalter of 1457, in which exact work was produced by painting, not by printing proper. That the performance of the press even on ordinary black work was slow, is indicated by the great number of presses used by the early printers, and is proved by the plain statement of Philip de Lignamine,
