Based upon the idea that oil and water do not mix, lithography is a printing process where an image is rendered on a flat surface and treated so that the "positive" parts of the image hold ink and the "negative" parts do not. The resulting print is a mirror image of the plate.
Significance
Developed in the 1700s, lithography is the basis for offset printing, the most common form of mass printing books, maps, posters and newspapers.
History
Bavarian author Alois Senenfelder invented lithography in the late 1790s as an inexpensive way to print his plays. Senenfelder began experimenting in 1796 with methods of using a smooth piece of limestone as a printing plate; by 1799 he had perfected treating the exposed and unexposed areas of text with different chemicals. Modern lithography uses flexible plates such as aluminum or mylar.
Misconceptions
Modern lithographic plates are not engraved. They are like giant photographic negatives, exposed to ultraviolet light to retain an image. With advances in computer technology, a printing plate can be exposed directly to a digital image for the printing process.
Function
The plates are attached to the cylinders of a printing press. They run through water, which the photographic emulsion repels from the area to be printed. The plates run through ink, then a rubber cylinder that acts like a squeegee before they transfer the image onto paper.
Fun Fact
Several artists have made lithographs as part of their portfolios--among them Henri de Toulouse-Lautrec, Pablo Picasso, M.C. Escher and Jasper Johns.
