planography

Planography is a printing process in which the image is created on a completely flat surface, or planographic plane. In planography, the image area is not raised or incised; instead, ink adheres to the image areas while the non-image areas are kept damp to repel ink. The key principle is the immiscibility of oil-based inks and water on the flat printing surface, which allows a continuous tonal range without relief or incised grooves.

The best-known form of planography is lithography, invented by Alois Senefelder in 1796. Lithography relies on drawing or treating a flat stone or metal plate with a grease-containing material to form the image; the surface is then dampened with water, and oil-based ink is applied. The ink sticks to the greasy image areas and is repelled by the water on the non-image areas, producing a print.

In modern practice, the term planography often encompasses offset lithography, where the image on the plate is first transferred to a rubber blanket and then to paper. This indirect transfer allows high-volume printing with reduced wear on plates and improved consistency. Contemporary lithographic plates may be metal or polymer, and digital workflows enable computer-to-plate production.

Planography is favored for its ability to reproduce smooth tonal transitions and both text and images on a flat substrate. It remains widely used in commercial printing for books, magazines, newspapers, and packaging.