Lithographs

Lithography is a method for printing on a smooth surface. It can be used to print text or artwork onto paper or another suitable material. It can also refer to a method of manufacturing semiconductor and MEMS devices. more...

Printing

The principle

In lithography the entire print block comes in contact with the paper sheet, and a chemical process confines the ink to the desired image on the block. This contrasts with relief printing where the ink is carried on a raised image, and intaglio, where it lies in the grooves of an incised image. Because the print block is flat rather than relief, lithography is described as a planographic print process.

The chemical process

Lithography works because of the repulsion of oil and water. The image is drawn on the surface of the print block with an oil-based medium. 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. This process is called etching. Using lithographic turpentine, the printer then removes the greasy drawing material, leaving only the salt layer; it is this salt layer which holds the skeleton of the image's original form. When printing, the stone or plate is kept wet with water. Naturally the water is attracted to the layer of salt created by the acid wash. Ink that bears a high lipid content, is then rolled over the surface. The water repells the grease in the ink and the only place for it to go is the cavity left by the original drawing material. When the cavity is sufficiently full, the stone and paper are run through a press which applies even pressure over the surface, transferring the ink to the paper and off the stone.

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