Planographic printing means printing from a flat surface, as opposed to a raised surface (as with relief printing) or incised surface (as with intaglio printing). Lithography and offset lithography are planographic processes that utilize the property that water will not mix with oil. The image is created by applying a tusche to a plate or stone.
Lithography, invented in Germany in 1798 and now considered the first and most important method of planographic printing (printing from a flat surface, or plane), is based on the chemical principles that oil and water do not mix but will attract like substances, and that both will adhere to a porous ground, such as a stone. The process came into widespread use in the 1820s as commercial printers and artists realized that images could be drawn as easily on stone as on paper, and that the stones could be reused. All methods of drawing could be used on the stone, including pen-and-ink, chalk, or crayon, and by about 1830 a watercolor-like wash, applied with a brush, was used to provide tints known as lithotints. Only after the development of cheaper printing methods such as wood engraving and lithography did it become possible to print inexpensive illustrated medical textbooks. Although lithographs could be produced more easily, and generally more cheaply, than relief or intaglio illustrations, color was still expensive since it had to be applied by hand and so was used only for relatively upscale colored scientific and medical books.
During the nineteenth century, lithographers perfected the art of printing in color by using multiple stones to achieve very complex colored images through a process known as chromolithography. Cheap color printing was then available for the first time in the history of printing. While the most pervasive use of chromolithography was in advertising, it was also used extensively for making popular prints as well as for scientific and medical illustrations.