In America this is accomplished by the McKee process, in which the plate is "made ready" and the make-ready impressed into its back through hydraulic pressure. The back of the plate is then shaved to proper thickness and the plate curved to fit the rotary cylinder.
The rapid printing of the McKee four-colour machines made it necessary to devise a method for quickly drying the sheets to prevent offset or smudge. This was at first accomplished by inter leaving the freshly printed sheets with specially prepared manilla paper. The device known as travelling offset prevents offsetting upon the impression cylinders of wet perfecting rotaries. It winds and unwinds (working backward and forward) around a reel which engages the second impression cylinder. This has given way to other methods, such as the spraying of a coat of powdered paraffin over the printed surface, so thin as to be imperceptible, but sufficient to prevent offsetting of the sheets.
Special inks are required for printing wet colours on the top of each other. The results cannot be said to equal those obtained when sufficient time is allowed for each colour to "set" before printing the following colour.
In newspaper production the reel-fed rotary has been brought to a high degree of efficiency. Although a newspaper machine is of great size and seems highly complicated, really it is simple. It comprises a number of units, each of which "perfects" a number of pages. If the pages exceed the number of plates which can be printed on a single unit, another unit or units can be linked up together, and the printed "webs" come to a point in proper sequence where they are folded and cut before delivery.
There is usually a blank space left on one or more pages of a newspaper for the purpose of publishing news which has arrived of ter the paper has gone to press. This late news is printed into the blank spaces by a contrivance called a "fudge box" which is circular in form and into which are secured lino type slugs. The "fudge" is fastened on to an auxiliary cylinder equipped with inking mechanism. This works in unison with one of the main impression cylinders and as the paper is printed an impression of the lines in the fudge box is made in the space left for the purpose. The "edition seals" and lines printed in colour in newspapers are produced by the same means.
There is in practice a very wide limit in the planning of a newspaper machine. Units can be arranged in a straight line or placed one on top of the other. The capacity is determined by the number of folders which it is possible to fit on the machine. Each of these can turn out 45,000 folded copies per hour. Not infrequently the paper is run through the machine at an approxi mate rate of 54 m. per hour and it is possible to join up new reels and change the fudge box without stopping the machine. (See BOOK ; PRINTING TYPE; COLOUR PRINTING; PHOTO-ENGRAV ING; also LITHOGRAPHY.)