Lithography—Today’s Popular Printing Process
AT NO time in history have printed words and pictures been produced in such volume. Homes and offices are flooded with magazines, newspapers, books, pamphlets, brochures, and so forth. The yearly sales of the printing industry in the United States is nearing $30 thousand million, up from $20 thousand million in 1967.
However, much of this printing today is done by a different process than before. It is done by lithography, rather than by letterpress. It is unlikely, though, that you have noticed the change.
Unless you are an experienced printer it is difficult to tell the printing process used, whether lithography or letterpress. Even with a magnifying glass a less experienced person may have trouble telling. There are, however, clues that can help you to distinguish between the two.
In letterpress printing, the ink tends to spread slightly from the pressure of the plate on the printed surface. A heavier ring of ink is created around each letter. Also, the pressure of the plate sometimes causes an embossing or denting of the paper, which shows on the reverse side. Lithography, on the other hand, has a smoother print, as well as a lack of impression since it is not reproduced from raised type.
There is also another major printing process—gravure—which is not as extensively used, although it is growing in popularity. The gravure process is just the opposite of letterpress in that the image on the printing plate is recessed or sunk instead of raised.
Growth of Lithography
Lithography is not new. It is a process that has been used for decades. Only in recent years, however, has it gained real popularity.
In 1925 only about 10 percent of commercial printing was done by lithography. By 1955 its share of the market had increased to 25 percent. Then in 1966 it bypassed letterpress, and now well over half of commercial printing is done by lithography. Gravure, on the other hand, has captured less than 10 percent of the commercial market.
There are some 19,000 commercial printing shops in the United States, and these account for over $8 thousand million in annual sales. When firms that print books, newspapers, magazines and other items are included, the number of printing establishments totals about 40,000. Many of these latter printing firms, which the industry distinguishes from commercial printshops, have also changed to lithography.
It is estimated that from about one half to three quarters of all books are produced by lithography. Such volumes as World Book Encyclopedia are produced by this process on presses that consume a five-and-a-half-mile web of paper in thirty minutes. The shift to lithography by newspaper and magazine printers has also been significant.
In the 1960’s about 3 percent of the newspapers in the United States were printed by lithography. By 1970 the percentage had risen to 61 percent! But since most large-city newspapers are printed by letterpress, there is still a greater volume of papers produced by letterpress. The St. Louis Post-Dispatch is the first large metropolitan daily newspaper to change to lithography; not long ago it ordered five lithographic web-offset presses.
Today more and more magazines also are being printed by lithography. It is estimated that about one third of the periodicals in the United States are printed by this process.
The shift to lithography, too, is reflected in the manufacture of printing presses. Sales of lithographic offset presses have bypassed and surged far ahead of sales of letterpresses. In 1970 the value of offset presses sold in the United States was $241 million compared to about $70 million worth of letterpresses sold. In Japan in 1969, $52 million worth of offset presses were made, whereas the value of letterpresses produced was only $19 million.
Why is lithography growing in popularity, even supplanting letterpress in certain fields? What are its advantages? What is the principle behind the lithographic printing process?
Origin and Development
Toward the end of the eighteenth century the German experimenter Senefelder discovered lithography. The name for this process was, at the time, very appropriate. The word lithography is from the Greek—lithos meaning ‘stone,’ and graphein meaning ‘to write’—so it literally means ‘to write on stone.’
That is exactly what Senefelder did in discovering this printing process. He drew on a certain kind of porous stone with a greasy crayon, and then moistened the stone with water. Then he applied a special ink to the stone. The ink adhered to the image drawn with the crayon, but not to the dampened areas. When a sheet of paper was pressed against the stone, the inked image was transferred to the paper.
Thus lithography is a printing process that is based upon the principle that grease and water do not mix. This process makes possible printing from a flat surface. The image to be printed is neither raised (as it is in letterpress) nor recessed (as it is in gravure), but it is on the same plane or level as the surface that surrounds it.
In earlier times lithography was used principally by artists to reproduce works of art, and to a limited extent it is still used for this purpose. But the principal use of lithography came to be in commercial printing. In the 1860’s power-driven flatbed presses were introduced in which stones served as printing plates. The stones used were as large as 44 by 64 inches and weighed many pounds.
These stone flatbed presses were all right for printing pictures, but were poor in reproducing the printed word. On the other hand, letterpresses excelled in printing the written word, but were badly limited in picture reproduction. Thus many books in earlier years were produced using letterpress for the verbal message and lithography for the pictures.
A revolution in printing occurred with the introduction of photography to the industry in the latter part of the nineteenth century. In adapting photography to lithography, the stone was first coated with a sensitizing solution. Then a strong light was passed through a negative of the image or type to be printed, projecting the image on the sensitized stone. After the stone was processed, the portions struck by the light were receptive to ink, and the parts of the stone that did not receive the light-projected image were water receptive. Thus only the ink-receptive image was printed on the paper.
Early in the twentieth century metal plates made of aluminum or zinc replaced the cumbersome stones. To give the smooth metal plates the water-receptive characteristic of the porous stone, they are roughened. A big advantage of these thin, flexible metal plates is that they can be used on rotary presses.
Another important development in lithography was an accidental discovery by a New Jersey lithographer named Ira Rubel. He noted that when an impression was first made onto a rubber blanket, and then the paper was printed from the blanket, the image was better than when the printing was done directly from the plate. In 1905 Rubel built a printing press that employed this principle of first transferring, or “offsetting,” the image to an intermediate cylinder before printing it.
Practically all lithographic presses today are offset presses. In the operation of these presses the plate cylinder first comes in contact with water-dampened rollers, and then with ink rollers. The water-dampened rollers wet the nonprinting areas of the plate; this prevents the ink rollers from inking these areas. Thus the ink rollers apply ink only to the printing image. This image is then offset from the plate cylinder onto the intermediate rubber-blanketed cylinder. The image is, in turn, transferred from the rubber-blanketed cylinder to the paper carried by the impression cylinder.
Why the Shift to Lithography
Increased production speed is a principal reason so many firms have shifted to offset presses. For example, a sheet-fed offset press may run twice as fast as comparable sheet-fed letterpresses, doing about 10,000 impressions per hour compared to 4,500. Also, in letterpress printing it takes considerable time to equalize the impression to print evenly, whereas this “makeready” operation is practically eliminated in lithography.
Another advantage of offset presses is that they make possible printing on a wide variety of materials—rough paper, tin, celluloid, and so forth—because of the resilient rubber blanket that transfers the image onto the material being printed. In addition, they produce printing of excellent quality, even as letterpress exponents acknowledge, although critics also note that some offset work is shoddy. As one said: “To achieve consistent results in web-offset requires a printer with first-rate machinery and press crews with exceptional ability and skill.”
No doubt a major reason why many have shifted to offset presses is that they are less expensive, in some instances costing less than half what a letterpress designed to do the same job will cost. “The economic side of offset lithography is probably the greater force for the use of the process,” one writer observed.
Increased production, greater economy, and quality printing—these are factors for the dramatic shift to lithography. And what about the future? Printing Magazine of February 1972 said: “It is safe to say that letterpress is fighting a losing battle and will continue to decline in relation to rotogravure, web offset, and sheetfed offset.”