lithography - Printing, Microlithography and nanolithography, Lithography as an artistic medium

A method of printing, invented by Aloys Senefelder in 1796, based on the principle that grease (ie ink) and water do not mix. A flat surface is treated so that the image area alone will attract ink. Ink and water are then applied to the surface; ink adheres to the image area and water to the non-image area. Paper is then brought into contact with the printing surface. In offset lithography, the modern form of this printing method, the image to be printed is created photographically and the printing plate is wrapped round a cylinder. When the plate cylinder has been inked and dampened, the image is transferred (‘offset’) to a rubber ‘blanket’ cylinder and then transferred again to the printing substrate (normally paper, but also metal and plastic).

Lithography is a method for printing on a smooth surface.

Printing

The principle

Lithography refers to a printing process that uses chemical processes to create an image. For instance, the positive part of an image would be a hydrophobic chemical, while the negative image would be water. Thus, when the plate is introduced to a compatible ink and water mixture, the ink will adhere to the positive image and the water will clean the negative image. This allows for a relatively flat print plate which allows for much longer runs than the older physical methods of imaging (e.g., embossing or engraving).

The chemical process

Lithography works because of the repulsion of oil and water. The image is drawn on the surface of the print plate with an oil-based medium (hydrophobic). The range of oil-based mediums is endless, but the dexterity of the image relies on the lipid content of the material being used--its ability to withstand water and acid. Following the placement of the image is the application of an acid emulsified with gum arabic. The function of this emulsion is to create a salt layer directly around the image area. The salt layer seeps into the pores of the stone, completely enveloping the original image. it is this salt layer which holds the skeleton of the image's original form.

The early process

Lithography was invented by Alois Senefelder in Bohemia in 1798, and it was the first new printing process since the invention of relief printing in the fifteenth century. After the oil-based image was put on the surface, acid burned the image onto the surface; During printing, water adhered to the gum arabic surfaces and avoided the oily parts, while the oily ink used for printing did the opposite.

Within a few years of its invention, the lithographic process was used to create multi-color printed images, a process known by the middle of the 19th century as Chromolithography.

The modern process

Modern high-volume lithography is used to produce posters, books, newspapers, packaging, credit cards, decorated CDs – just about any smooth, mass-produced item with print on it.

In this form of lithography, which depends on photographic processes, flexible aluminum or plastic printing plates are used in place of stone tablets. A photographic negative of the desired image is placed in contact with the emulsion and the plate is exposed to light. After development, the emulsion shows a reverse of the negative image, which is thus a duplicate of the original (positive) image. The image on the plate emulsion can also be created through direct laser imaging in a CTP (Computer-To-Plate) device called a platesetter. The positive image is the emulsion that remains after imaging.

The plate is affixed to a drum on a printing press. Rollers apply water, which covers the blank portions of the plate but is repelled by the emulsion of the image area. Ink, applied by other rollers, is repelled by the water and only adheres to the emulsion of the image area--such as the type and photographs on a newspaper page.

If this image were directly transferred to paper, it would create a positive image, but the paper would become too wet. The paper rolls across the blanket drum and the image is transferred to the paper. Because the image is first transferred, or offset to the rubber drum, this reproduction method is known as offset lithography or offset printing.

Many innovations and technical refinements have been made in printing processes and presses over the years, including the development of presses with multiple units (each containing one printing plate) that can print multi-color images in one pass on both sides of the sheet, and presses that accommodate continuous rolls (webs) of paper, known as web presses. Current dampening systems include a "delta effect" which slows the roller in contact with the plate, thus creating a sweeping movement over the ink image to clean impurities known as "hickies".

The advent of desktop publishing made it possible for type and images to be manipulated easily on personal computers for eventual printing on desktop or commercial presses. The development of the digital platesetter in the late twentieth century eliminated film negatives altogether by exposing printing plates directly from digital input, a process known as computer to plate printing.

Microlithography and nanolithography

Main article: nanolithography.

Microlithography and nanolithography refer specifically to lithographic patterning methods capable of structuring material on a fine scale.

In addition to these commercially well-established techniques, a large number of promising microlithographic and nanolithographic technologies exist or are emerging, including nanoimprint lithography, interference lithography, X-ray lithography, extreme ultraviolet lithography, and scanning probe lithography.

Lithography as an artistic medium

During the first twenty-five years of the nineteenth century, the practice of lithography was predominantly restricted to cheap reproductions of paintings and drawings. However, around 1825 the French artists Ingres, Géricault, Delacroix, and Rodolphe Bresdin embraced the process as a way to avoid the problems inherent in wood-block and copper engraving, namely, the near necessity of middlemen like draughtsmen (who transferred the image to the wood or copper plate) and engravers (who carved the image out of the plate). The advantage to lithography (for an artist's point of view) was that he or she could draw or paint directly onto the lithographic material and avoid entirely the intermediate steps and craftsmen involved in engraving.

Goya's lithographs The Bulls of Bordeaux (1828) and Delacroix's illustrations to Goethe's Faust were the groundbreaking "artist's lithographs" that sparked a flood of (mostly French) artists who dabbled in lithography, including Prud'hon, Cezanne, Manet, Toulouse-Lautrec, and, of course, its greatest practitioner, Daumier, whose prints began to appear in the 1830s.