Lithography
Lithographic printing was discovered in 1798 at Munich. For nearly 20 years, this process—in which the image to be printed can be rendered on a flat surface and chemically treated to retain ink in image areas and repel ink in nonimage areas—was held a closely guarded secret, until first published in 1818. The process of preparing porous limestone blocks for continuous-tone hand printing has remained essentially unchanged since that time. The materials and procedures of the 19th-century lithographer are duplicated in almost every respect in contemporary fine-art lithography printing.
An image is drawn with tusche and litho crayon (carbon pigment in liquid and solid forms) onto the printing surface, before the image is fixed, moistened, and inked in preparation for printing. The printing is done on a press that exerts a sliding pressure. Because it undergoes virtually no wear in printing, a stone can yield almost unlimited copies, however, in fine-art printmaking only a specific number of prints are pulled, signed, and numbered before the stone is cancelled (defaced). Techniques and materials developed in the 20th century—such as improved chemistry and printing on metal plates—has varied the process, though many artists continue to prefer the time-honored method and tradition.
Intaglio
Intaglio is printing from the recessed areas below the surface of a metal plate or other substrate (i.e. copper, zinc, aluminum, plastics or even coated paper) — and is distinguished from relief printing which is printing from the areas above the surface. Images are cut, scratched or etched into the plate or printing surface, viscous ink is rubbed into the incisions or grooves, and the surface is wiped clean. Using a roller press to print, wet printing paper is embossed with considerable pressure into the incised lines or recessed areas of the plate. Various intaglio techniques include engraving, etching, drypoint, aquatint, and mezzotint which can produce a wide range of visual effects.
Relief
In contrast to intaglio, relief is printing from the areas raised above the surface of a block, plate or other substrate (i.e. wood, linoleum, aluminum, zinc, magnesium and plastic). Areas not to be printed can be cut or etched away to leave the design standing in relief — or, instead of cutting away the background, a relief can be created by building upon the surface. The surface is inked using a roller or a dabber, a sheet of paper is placed on top, and pressure applied by hand or using a printing press. Common types of relief processes include woodcut, linocut, and wood-engraving. Relief and intaglio processes can sometimes be combined by first applying ink to the depressions (intaglio) and then rolling the raised surfaces (relief) for interesting visual effects.