planography
A form of printing from a flat surface, as opposed to a raised or incised one.
planography: printing from a flat, chemically prepared surface
Planography is a printing method in which the image and non-image areas exist on the same plane, differentiated only by their chemical properties rather than physical relief or depression. The printing surface is neither raised (as in letterpress) nor recessed (as in gravure), but flat throughout. The most common and industrially significant form is lithography, where oil-based ink adheres to greasy image areas while water-based fountain solution keeps non-image areas repellent to ink.
The term derives from Greek planos (flat) and graphia (writing or drawing). Unlike relief printing, where unwanted material is removed, or intaglio printing, where ink fills recessed lines, planographic processes rely on the mutual repulsion of oil and water. Traditional lithography uses limestone or specially grained aluminum plates; the artist draws with a greasy lithographic crayon, then chemical processing fixes the image and conditions the blank areas to reject ink during printing.
Modern planographic printing is dominated by offset lithography, where the image transfers from a treated metal plate onto a rubber blanket, which then transfers it to paper. This indirect path offers significant advantages: the rubber surface conforms to uneven substrates, reduces plate wear, and allows printing on rough materials. Most commercial multicolor printing, from packaging to newspapers, relies on offset lithography despite the process requiring careful control of ink-water balance.
Because planographic printing depends on chemical rather than mechanical differentiation, image quality is highly sensitive to water content, ink viscosity, and temperature. Too much water causes the non-image areas to accept ink; too little causes emulsification and spreading. Skilled press operators monitor and adjust fountain solution composition continuously during production runs. Modern presses incorporate conductivity meters and automated dampening systems to maintain tight tolerance.
Planography sits between the precision of gravure (which can reproduce fine detail but is expensive to set up) and the simplicity of flexography (which is fast but limited in tone range). It remains the preferred process for fine art prints, high-quality commercial reproduction, and applications where both speed and image fidelity matter. Digital plate imaging has made setup faster and more repeatable, though the fundamental chemistry of the process has changed little since Alois Senefelder's invention around 1796.