Wiki Explains Litho Printing

Lithography uses simple chemical processes to create an image. For instance, the positive part of an image is a water-repelling ("hydrophobic") substance, while the negative image would be water-retaining ("hydrophilic"). Thus, when the plate is introduced to a compatible printing ink and water mixture, the ink will adhere to the positive image and the water will clean the negative image. This allows a flat print plate to be used, enabling much longer and more detailed print runs than the older physical methods of printing (e.g., intaglio printing, letterpress printing). Lithography was invented by Alois Senefelder in Bohemia in 1796. In the early days of lithogra. To read more click on the following link.

http://en.wikipedia.org/wiki/Lithography