lithography, type of planographic or surface printing. It is distinguished from letterpress (relief) printing and from intaglio printing (in which the design is cut or etched into the plate). Lithography is used both as an art process and as a commercial printing process. In commercial printing the term is used synonymously with offset printing.

The Process

All planographic printing is based on chemical action, and lithography is based on the mutual antipathy of oil and water. As the name [Gr.,=writing on stone] implies, a lithograph is printed from a stone (except in commercial processes, where grained metal or plastic plates are employed). The process was invented c.1796 by the playwright Aloys Senefelder, and the Bavarian limestone that he employed is still considered the best material for art lithography.

The slab of stone is ground to a level surface, which may be of coarse or fine texture as desired. The drawing is made in reverse directly on the stone with a lithographic crayon or ink that contains soap or grease. The fatty acid of this material interacts with the lime of the stone to form an insoluble lime soap on the surface, which will accept the greasy printing ink and reject water. Accordingly, those parts of the stone that have been drawn upon have an affinity for ink.

Sometimes the drawing is made on paper and transferred to a heated stone by pressure. This is known as a transfer lithograph and does not require the artist to reverse his or her drawing. Next, the surface of the stone untouched by grease is desensitized to it, and the portions drawn upon are fixed against spreading by treatment with a gum arabic and nitric acid solution. The grease has now penetrated the stone, and the drawing is washed off with turpentine and water. The stone is ready to be inked with a roller and printed, but it must be kept moist. The printing requires a special lithographic press with a sliding bed passing under a scraper.

Applications

As a printing process lithography is probably the most unrestricted. It produces tones ranging from intense black to the most delicate gray as well as a full range of colors. It also simulates with equal facility the effects of pencil, pen, crayon, or brush drawing. White lines are readily produced by scratching through the drawing on the stone. Several hundred fine proofs can be taken from a stone. The medium was exploited by many artists in the 19th cent., including Goya, Delacroix, Daumier, Gavarni, Manet, Degas, Bonnard, Whistler, and Toulouse-Lautrec, whose posters are among the most celebrated lithographic masterworks. In the United States, A. B. Davies, George Bellows, Joseph Pennell, and Currier and Ives are among the many artists noted for their lithographs.

For the commercial reproduction of art works, photolithography has played an increasingly important role. In this process a photographic negative is exposed to light over a gelatin-covered paper. Wherever the light does not strike the gelatin, the latter remains soluble while the other parts are rendered insoluble. When the soluble portions are washed away, the pattern to be printed can be inked and transferred to the stone or plate. Color lithography and color photolithography require as many stones or plates as the number of colors employed. The commercial printing applications of the lithographic process are vast in scope and almost unlimited in number.

or offset lithography or litho-offset

In commercial printing, a widely used technique in which the inked image on a printing plate is imprinted on a rubber cylinder and then transferred (offset) to paper or other material. The rubber cylinder gives great flexibility, permitting printing on wood, cloth, metal, leather, and rough paper. In offset printing the matter to be printed is neither raised above the surface of the printing plate (as in letterpress printing) nor sunk below it (as in intaglio, or gravure, printing). Offset printing, a development of lithography, is based on the principle that water and grease do not mix, so that a greasy ink can be deposited on grease-treated printing areas of the plate, while nonprinting areas, which hold water, reject the ink. The offset plate is usually of zinc or aluminum or a combination of metals, with the surface treated to render it porous and then coated with a photosensitive material. Exposure to an image hardens the coating on printing areas; the coating on nonprinting areas is washed away, leaving wetted metal that will reject ink. Seealso xerography.

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Printing process that makes use of the immiscibility of grease and water. Aloys Senefelder of Prague (1771–1834) exploited the properties of a stone with a calcium carbonate base and a fine, porous surface, and perfected his printing process in 1798. In Senefelder's process, the stone, with a design drawn on it with crayon or greasy ink, was wetted with water; after various etching and protecting steps, it was brushed with oily ink; it retained the ink only on the design. This inked surface was then printed—either directly on paper, by a special press (as in most fine-art printmaking), or onto a rubber cylinder and thence onto paper (as in commercial printing). The method of preparing stones for hand printing, still the lithographic method preferred by artists, has hardly changed. Commercial lithographic printing on a modern rotary offset printing press can produce high-quality, finely detailed impressions at high speed, reproducing any material that can be photographed in the platemaking process. It now accounts for more than 40percnt of all printing, packaging, and publishing, more than twice the percentage produced by any other single printing process.

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