What is Lithography?



Lithographic method is extensively used for printing office and bank stationery, stock and share certificates, diplomas and degree certificates, and other forms. Lithography, also called offset, is used in the production of paintings and art subjects, magazine covers, book jackets, calendars, charts, posters, drawings, maps, display cards, children's books, text-books, advertising literature, and artistic labels and cartoons.

In brief, lithographic printing has special advantages when the copy to be reproduced includes photo­graphs and drawings, more so when these are in colour.

That is why it is used more frequently for display jobs, especially those requiring large print orders. Because of lower cost of production and better quality of finished jobs, this method is growing very fast.

There are four main departments (excluding bindery) in lithographic printing presses: photo, art, plate-making and printing. Workers in each of these perform specific duties connected with the lithographic process, though in small lithographic shops workers have to be skilled in more than one occupation.

The Photo-Lithographer also called Lithographic Camera­man, Cameraman/Camera Operator, photographs original art work (whether pictorial or illustrative) in black and white or in colour, typewritten or typeset composed matter on film or glass to obtain a (line, half-tone, continuous tone, or colour) negative that, in turn, becomes a 'copy' which is to be transferred to lithographic plates.

After mounting (placing) illustrations or typeset material on copy board of copying frame, he adjusts lights and camera, focuses with the help of ground-glass focusing screen, loads plate in a dark room, mounts the loaded plate on camera and exposes it (film or glass plate) to material (copy).

Using a screen, he breaks up shadings of the copy into dots for half-tone printing. He also uses colour filters for preparing separate colour-wise plates for printing; and then dries film or plate negative, thus obtained. At times, he is also called upon to make a positive film or glass plate.

In large lithographic presses, individual cameramen almost always specialise either in black-and-white or in colour photography. Alternatively, they may specialise as a process photographer, half­tone photographer or line photographer.

(i) The Lithographic Re-toucher:

After negatives have been made and developed, they frequently need re-touching to lighten or intensify certain parts, after the photographic process has broken up the lines, images, and designs of the printed material into a series of small dots. Making corrections by sharpening or re-shaping dots is a highly skilled task, and is done by hand with the use of chemicals, dyes and special devices.

The Lithographic Retoucher (also called Lithographic Process Artist, Colour-Artist Retoucher, or Tone Artist) corrects film or glass plate, negative or positive, by comparing with the original copy and determining where, and how much, correction is necessary. He refines and corrects imperfections in designs on lithographic plates by drawing on them with scribbling tools, crayons, pen and ink, etc. to make them fit for printing. In the process, he has to intensify or reduce unsatisfactory tone values, to blank out unwanted portions of nega­tives or positives, to add missing details, to change shades of colours to apply tints to photographic plates (film or glass) and lithographic printing plates by brushing tint through a fine screen, or to correct colours in the final press plates.

(ii) The Lithographic Artist draws posters, maps, or other pictures on polished or grained stone or metal (zinc or aluminium) plates or on special (transfer or glazed) paper, when hand methods are used in place of photo-mechanical methods. He may produce key patterns either by copying or creating original designs with soft greasy crayons or pen-and-ink for Subsequent processing and printing. Lithographic artists may specialise in various media, and are known as Stone Engravers: Ben-Day artist (using Ben-Day's medium; Opaquer and Tuscher (who blanks out, outlines or shades portions of negative or positive film with lithographic ink called tusche).

Photographic negatives or positives, made by cameraman and corrected by artists, are transferred to press plates by workers in the plate making department. This is done usually by hand and at times by machine.

(iii) When hand method is adopted, the Photo-Plate Maker transfers impressions from photograph negative to metal plates for subsequent processing for direct use in lithographic printing; covers the surface of the grained metal plate usually zinc copper or alumi­nium, with a coating of photo-sensitive chemicals. After the plate has dried, the negative or positive is placed in contact with the sensitized plate and exposed under strong arc lights, after which it is developed with photo-developing chemicals. The image is thereby formed on the plate from the negative or positive.

When the machine method is used, the plate worker exposes the prepared plate and the photographs in a vacuum printing frame or photo-composing machine. The plate is then developed and chemically treated to bring out the image.

The "Plate" is then passed on to the press machine section for printing.

Before printing, a Proofer takes proof from a hand-operated offset press, by applying ink to plate with a hand roller and turning crank to rotate rubber-blanket roller against plate and over paper to transfer image to proof paper.

There are numerous other semi-skilled workers to assist the workmen in the studio, art room or workshop.