Discovery of offset (early 20th century)

At the same time, lithography was undergoing a new evolution. After the first mechanical presses had been perfected, this process had developed along two lines: (1) printing on thin sheets of metal (for example, tinplate for packaging canned foods) using a transfer process (1878) in which the impression cylinder carrying the metal sheet to be printed did not come in contact with the stone but did with an intermediary cylinder covered with rubber, the blanket, which transferred the image from the stone to the metal; and (2) printing on paper, which was done only comparatively infrequently in the last years of the 19th century, on cylinder or rotary presses.

In 1904 at Nutley, New Jersey, an American printer, Ira W. Rubel, discovered that an image accidentally transferred from the plate cylinder of his rotary to the rubber blanket of the impression cylinder during a paper-feed stoppage could itself be used for printing and in fact produced a superior impression. Rubel and an associate constructed a three-cylinder press, the first offset press, the term since used to describe this increasingly popular printing device.

Dry offset (1920)

A few years later a problem arose in connection with printing the background of checks with a water-soluble ink to prevent forgeries. It was proposed that the lithographic plate of the plate cylinder be replaced with a stereotype plate or with a letterpress wraparound plate. This process, which combines the relief of letterpress, which does not require wetting, with the transfer of offset, is known as dry offset, or letterset. Its area of application is not limited to check backgrounds but is used in all areas of conventional printing.

Since 1950 another process has been developed, particularly in the United States. It combines rotogravure with the transfer of offset for printing wallpapers, plastic floor coverings, paper plates, and other products.

Colour printing

As early as 1457 a psalter, which Peter Schöffer signed but which some researchers now attribute to Gutenberg, included, in imitation of the contemporary illuminated manuscripts, paragraphs beginning with ornamental capital letters printed in two colours. This was accomplished by the use of two wood blocks that fitted one inside the other and could be separately inked.

Experiments to reproduce pictures in several colours on wood blocks were made in Germany in the 16th century. In the 17th century, different inks were applied to the different parts of the same engraved metal plate in such a way that all the inks were transferred to the paper in a single pressing. In 1719 a painter, Jacques-Christophe Le Blond, took out a patent in England for a process that used the three primary colours, blue, yellow, and red, and black for outlining shapes. Using a dense grid, he engraved four metal plates, bringing out on each plate the relative importance of the colour involved. The same sheet of paper then went through four successive impressions, each in a different colour.

In the 19th century the scientific definition of the principles of trichromatism, the enunciation of the fundamental theories of three-colour analysis and synthesis of colours by photography, the perfecting of coatings selectively sensitive to colours, and finally the use of the screen, instead of Le Blond’s hand-drawn grid, established the modern trichromatic technique (which becomes quadrichromatic when black is also used).

Automation of composition (after 1929)

The search for maximum efficiency had from the very beginning posed the problem of both the mechanization and the automation of composition. The Monotype system, with its separation of keyboard and caster, had constituted one approach to the solution, since the same caster could work at full speed when fed with perforated tapes produced on several keyboards.

The perfection of teletypesetter remote-control composing equipment in the United States by about 1929 permitted widespread application of the principle of separation of human function on the one hand and mechanized function on the other. The operator produces a tape on which each letter, symbol, and space is represented by a combination of perforations. A translator device reads the tape and, according to each combination of holes, orders the release of the necessary matrices for letters, signs, and justifying spaces. Machines casting one-piece fully spaced lines or slugs are able to produce more than 20,000 characters per hour.

Programmed composition (1950s)

The production of the perforated tape remained relatively slow, however, because of the time taken by the operator to decide where to make the division in a word at the end of a line. Eventually, in the second half of the 20th century, electronics provided the means of automatically making this decision.

In the 1950s the BBR system, named by the initials of three inventors in France, introduced programmed composition. Starting with a perforated tape continuously produced by the operator, a computer takes over the task of determining the length of lines, the places where words are to be divided according to grammatical rules and typographic usage, the integration of corrections, and even the presentation of the text according to the layout. The speed at which a final tape bearing this information can be produced is limited only by the performance of the perforator, which is the outlet device of the computer. Operating speeds have exceeded 300,000 characters per hour, or 10 times the capacity of the most modern slugcasting machines.

During the 1960s, perforated tape began to be replaced by magnetic tape, which is even more rapidly made, at a rate of about 1,000 characters per second, or 3,600,000 per hour. Although magnetic tape is useless for mechanical composers casting pieces of type or lines in lead, such speed is practical for other kinds of machines not burdened with the weight of lead and the inertia of their mechanical components.