Planografie

Planografie, or planographic printing, is a printing method in which the image is produced on and transferred from a flat surface. The key principle is that the printing surface remains level and non-recessed or non-raised; ink is applied to the flat surface in the image areas while the non-image areas are kept damp and repel the ink. This contrasts with relief printing, where the image is raised, and with intaglio, where the image is incised below the surface.

The most common planographic process is lithography, invented by Alois Senefelder in the late 18th century. Lithography relies on the chemical contrast between oil-based ink and water on a grease-receptive image drawn on a flat substrate, historically limestone and later metal or polymer plates. The surface is kept damp so water repels the ink on non-image areas. In modern lithography, a dampening system provides the water, and inked image areas transfer to a blanket cylinder before being pressed onto paper in offset lithography.

Planography encompasses several variants. Offset lithography, the dominant commercial form today, uses a rubber blanket to transfer the image from the plate to the paper, enabling high-speed, consistent printing and easy adaptation to different substrates. Other planographic methods were developed for art printing or specialized applications, but lithography remains the principal example of planographic printing.

Applications include books, newspapers, posters, packaging, and fine art prints. Advantages of planography include flat-image quality, fine detail, and efficiency for large runs; disadvantages involve the need for precise dampening control and specialized machinery.