quality:corruption
Function and approach

A printing press, in its classical form, is a standing mechanism, ranging from 5 to 7 feet (1.5 to 2.1 m) long, 3 feet (0.91 m) wide, and 7 feet (2.1 m) tall. The small individual metal letters known as type would be set up by a compositor into the desired lines of text. Several lines of text would be arranged at once and were placed in a wooden frame known as a galley. Once the correct number of pages were composed, the galleys would be laid face up in a frame, also known as a forme, which itself is placed onto a flat stone, 'bed,' or 'coffin.' The text is inked using two balls, pads mounted on handles. The balls were made of dog skin leather, because it has no pores, and stuffed with sheep's wool and were inked. This ink was then applied to the text evenly. One damp piece of paper was then taken from a heap of paper and placed on the tympan. The paper was damp as this lets the type 'bite' into the paper better. Small pins hold the paper in place. The paper is now held between a frisket and tympan (two frames covered with paper or parchment).

These are folded down, so that the paper lies on the surface of the inked type. The bed is rolled under the platen, using a windlass mechanism. A small rotating handle called the 'rounce' is used to do this, and the impression is made with a screw that transmits pressure through the platen. To turn the screw the long handle attached to it is turned. This is known as the bar or 'Devil's Tail.' In a well-set-up press, the springiness of the paper, frisket, and tympan caused the bar to spring back and raise the platen, the windlass turned again to move the bed back to its original position, the tympan and frisket raised and opened, and the printed sheet removed. Such presses were always worked by hand. After around 1800, iron presses were developed, some of which could be operated by steam power.

The function of the printing press was described by William Skeen in 1872:

this sketch represents a press in its completed form, with tympans attached to the end of the carriage, and with the frisket above the tympans. The tympans, inner and outer, are thin iron frames, one fitting into the other, on each of which is stretched a skin of parchment or a breadth of fine cloth. A woollen blanket or two with a few sheets of paper are placed between these, the whole thus forming a thin elastic pad, on which the sheet to be printed is laid. The frisket is a slender frame-work, covered with coarse paper, on which an impression is first taken; the whole of the printed part is then cut out, leaving apertures exactly corresponding with the pages of type on the carriage of the press. The frisket when folded on to the tympans, and both turned down over the forme of types and run in under the platten, preserves the sheet from contact with any thing but the inked surface of the types, when the pull, which brings down the screw and forces the platten to produce the impression, is made by the pressman who works the lever,—to whom is facetiously given the title of "the practitioner at the bar.".