The Work in the Lithographing Plant
( Originally Published 1930 )
The Operations Performed.—When a lithographic job is desired, the first thing required is a design which will fully represent the idea of the advertiser or the person who puts in the order. Sometimes the customer knows exactly what he wants, but in many cases he depends upon the designer to furnish him with the idea as well as with the design. The work of the commercial designer consists in lettering the designs and in designing letter-heads, while the art designer is the man who draws and colors the pictures and the figures that appear on magazine covers, posters, and advertisements of all kinds. The designer first draws the picture or letters it and puts in all the colors that are desired, if any. The plate artist then prepares as many different plates as there are colors in the drawing. Later on, the pressmen will be required to print the job as many different times as there are colors in the design. Thus if the job requires five colors, the plate artist must make five different plates, and the pressmen must print the job five times.
When the design is completed, it is sent either to the engraving department or to the art department. In case the design is to be engraved, it is given to the stone engraver who lays a thin sheet of transparent gelatine over it and makes a tracing with a steel needle. He then rubs a solution of nitric acid and gum arabic over the limestone, which has been polished until it is smooth, in order to make it resist grease. The tracing is now laid on the stone and rubbed down with a blue powder until the design appears on the stone, after which the engraver scrapes it in with a steel-pointed needle. Then a greasy ink is applied to the design, and it is ready for the proofer and the transferrer. The engraver may also draw the design directly on the unetched stone with a greasy ink or crayon which goes into the surface. When this is done, he puts a solution of acid and gum arabic on the stone to close up the pores where there is no grease. This makes it possible for those parts to throw off the ink when they are dampened, while the greasy parts will take up the ink and throw off the water.
The plate artist draws directly on very thin zinc of aluminum plates. He makes pencil sketches of the original color designs which have been sent from the designing department. Then he makes a tracing on a thin sheet of gelatine, dusts it with red chalk, places it on a zinc plate, and rubs it well until the design appears on this plate. He makes a different plate for each color. The next step consists in drawing on these plates with lithographic ink in such a manner that the inked parts on each plate will print in different color values when placed on the press. After this is done, the proofer etches the plate with etching fluid. This fluid does not eat away the blank parts of the plate, but it does change the surface chemically so that the design attracts ink while the other portions throw off the ink when they are properly dampened. Thus in the lithographing process the design is not raised above the surface of the plate as it is in the type-printing process. The most modern and up-to-date plants also use the photo-lithographing method in which the design or drawing is photographed on photographic plates. Then specially trained men are employed to retouch these plates to correspond to the color values on the original design.
The proofer works in the proofing or proving department. His job is to make proofs of every plate and to determine what colors to use. He uses a hand offset press with which he pulls his proofs. In addition to making separate proofs of each plate, he makes a proof of the completed poster, the magazine cover, or the article upon which he is working. He fastens all of them together to form what is called the progressive proof. When the proofer receives the plates, he etches them with an acid to make the parts outside of the design able to resist ink. Then he inks or rolls up the plate with a hand roller. In the next operation, which is performed on the hand-offset press, he makes an impres sion on a rubber blanket spanned around a cylinder by rolling it over the plate. After this is done, the proofer rolls this rubber blanket over a sheet of paper in order to transfer the impression to it. Thus the zinc plate does not touch the paper directly. Before the proofer can perform this operation, he must mix his inks to conform to the colors which the artist has used in the original drawing. This is a very important part of his work because the pressman later on mixes his colors to look exactly like those on the proof. When the proofer has completed his work, he sends the plates to the transfer department.
The original zinc plates which have been prepared by the plate artist are not used in the pressroom, but are kept on file for future needs. The transfer-department workers are the ones who prepare the press plates from the originals. They are called transferrers or transfer-men. In their work of transferring designs from one plate to another they use a special kind of paper which is called transfer paper. This paper is covered with a preparation of starch and glycerine when it is received at the lithographing plant. When the transferman gets the original plate, he inks it with transfer ink, places a sheet of transfer paper on it, and pulls it through the hand transfer press. He does this for as many times as he desires impressions on the transfer paper. As a rule, the press plates are much larger than the originals, and it is possible to put many different designs on them. In the next operation the transferman sticks on to a key plate these impressions. This key plate is made of a sheet of zinc covered with paper, and it corresponds to the size of the plate desired for the particular job. The transfer impressions are placed on the key plate in a previously determined order so that an accurate register is obtained. This is necessary if each color is to be printed in the right place on the completed product. The key plate is then placed face down on a zinc press plate in a transfer scraper press, and pressure is exerted. This pressure causes the transfer paper to stick to the plate. When the transfer paper is removed by dampening, the design leaves it and remains on the zinc plate. The transferman then etches it with a solution of gum arabic and acid, in order to make immune to ink those parts of the plate which do not have a design on them. It is then ready for the press.
Several types of presses are used in lithographic press-rooms, although one kind, the offset press, is now the most popular. It is used most extensively in those plants that have adopted the zinc-plate method of lithographic printing. Flat-bed stone presses are used to a certain extent, but only when special jobs are required or demanded. The offset press is different from the other presses because, instead of printing directly from the plate on the paper, it prints upon a rubber covered cylinder which transfers the impression to the paper. Thus, it has three cylinders, the plate cylinder which carries the plate, the blanket cylinder which carries the rubber blanket, and the impression cylinder which carries the sheet of paper. Offset pressmen and pressfeeders perform the various operations. When the plate is brought in from the transfer department, the pressman clamps it around the plate cylinder and fastens a thin rubber blanket around the blanket cylinder. The ink which he has previously prepared is already in the fountain. The pressman removes the gum arabic coating from the plate and allows the plate to revolve so that it is dampened by water. The water prevents the ink from sticking to the blank parts of the plate. When the plate revolves again, the ink is deposited on the design which is greasy and is, therefore, not affected by the water. The feeder then puts a sheet of paper into the feeding mechanism. This sheet receives the impression from the blanket cylinder which has come in contact with the plate cylinder. The printing operation is then carried on until the run is completed. In the lithographic printing process only one color can be printed at a time. In order to save time, the larger plants run each color of a design on a different press. Thus the sheets are transferred from press to press until the job is finished.
The cutting, the sorting, and the packing of the completed jobs are performed after the printed sheets have dried. The press plates are returned to the plate-making departments where the designs are removed with lye, and the plates are regrained so that they can be used again.
The Tools and Materials Used.—Hand tools mainly are used in this industry to perform the operations required. In the art department the workers make use of crayons, brushes, squares, pencils, paint of different colors, paper, and lithographic ink. The engravers do their work with squares made of steel, lithographer's needles, paper and pencil, gelatine sheets, blocks of lithographic stone, and brushes. Lithographic crayon-and ink, brushes, solutions of gum arabic and acid, are the main tools and materials with which the plate artist works. The proofers carry on their operations by means of leather-covered rollers, with which they ink the plates, and also by means of hand-offset presses, scraper and pallet knives, squares and rules, sheets of paper, and inks of various colors. The tools and the materials used in the transfer department are about the same as those used in the proofing department, with the exception of transfer presses and transfer paper. The pressman's tools are mixing knives and all sorts of wrenches which are required to adjust the presses and to fasten the plates. Inks and sheets of paper are used in the printing process.