What is Lithograph?
The artist draws an image directly on a highly polished limestone using a grease based crayon, or grease based liquid called tusche, similar to a paint. The stone is then prepared for printing by applying a chemical solution of gum arabic and nitric acid to make it more receptive to water. In order to make the print, the stone is dampened with water, which will not adhere to the image drawn because of the natural antipathy of grease to water. When ink is rolled over the stone, it will only adhere to the grease based image. Then the paper is pressed against the stone, and only the ink on the greasy image is transferred. The image is then printed on paper.
Aloys Senefelder, who invented lithography in 1798, preferred to call it "chemical printing", since the process depends on the chemical interaction of grease, nitric acid, gum arabic, and water, rather than the stone from which the name lithography is derived.
Lithography became a popular printing technique because exact replicas could be made that were like drawings on paper without degradation of the image.
To create a color lithograph, a seperate stone for each color is used and must be printed separately through careful alignment or registration. This process is typically done by artists most frequently in limited edition prints.