What is lithography and offset lithography

Lithography, comes from Greek : lithos meaning stone and grapho meaning to write. Invented in 1796 as a method of printing on limestone and originally using oil or fat.

Lithography uses the principle that oil and water don't mix as the basis of the printing process. A flat stone such as limestone or a metal plate is treated so that the image area attracts oil-based inks and the wet non-image areas repel the oil-based inks. In lithography, the printing surface is flat with both image and non-image areas at the same level on the printing plate.

One of the most commonly used printing process' to create reproductions, today, is a method called Offset Lithography. How this process works is first transferring an image photographically to thin metal, paper, or plastic plates. Rollers apply ink and water to the plates. Since oil and water don't mix, the oil-based ink doesn't adhere to the non-image areas. Only the inked image portion is then transferred to a rubber blanket (cylinder) that then transfers the image onto the paper as it passes between it and another cylinder beneath the paper. The term offset refers to the fact that the image isn't printed directly to the paper from the plates, but is offset or transferred to another surface that then makes contact with the paper.