BOTANICAL ART IN PRINT - Planographic Prints
A planographic surface can be either a porous stone, such as limestone, or a metal plate. The process, also referred to as lithography, was invented in 1798 and is based on the fact that oil and water repel each other.
Unlike wood or metal engraving, the image for a lithographic print is drawn onto a flat piece of stone with a greasy crayon, pencil, or ink. The remainder of the surface, being porous, will absorb water. When the entire plate is wetted, the greased image will repel the water, and the porous areas will soak up the water. Oil-based ink is rolled onto the stone where it adheres to the greased image areas and is repelled by the wetted areas. When paper is applied to the stone, the greased inked areas are transferred to the paper to produce the lithographic image.
Lithography had two advantages over previous methods of printing. Lithographs were much cheaper to produce than etchings on steel or copper. But perhaps more importantly it was the only printing method that allowed artists to draw directly on the printing surface; artists were able to maintain a fine degree of control over their work by eliminating the need for an artisan to replicate their images on a working surface.
Color was applied to early lithographs by hand, but eventually the application of several colors became possible by utilizing multiple stones, each with a different area of color. Referred to as chromolithographs, these prints would pass through the printing press as many times as there were areas of color.