What is offset printing?
In commercial printing, offset printing, also known as offset lithography or litho-offset, is a commonly used printing technique in which an inked image on a printing plate is printed on a rubber cylinder before being transferred (i.e., offset) to paper or other medium. The rubber cylinder allows for a wide range of printing applications, including wood, fabric, metal, leather, and rough paper. Ira W. Rubel of Nutley, New Jersey, discovered the process by accident in 1904 and quickly built a press to use it.
The subject to be printed in offset printing is neither elevated above the surface of the printing plate (as in letterpress) nor sunk below it (as in screen printing) (as in intaglio, or gravure, printing). Instead, it is flush with the plate’s surface, classifying offset as a planographic printing method.
Etched metal plates, water-repellent (e.g. oil-based) inks, water, blanket cylinders, and impression cylinders are all used in the offset lithography process.
Oily inks only adhere to the sections of the plate that contain the images and text. Oil-based inks are repelled by a thin layer of water applied to the plate’s blank areas. The ink on the plates is first transferred to a “blanket” cylinder coated in rubber. When the inked blanket cylinder rolls over the paper, the ink reaches the paper.
Impression cylinders were used on many presses to exert pressure to the paper while the ink was transferred to the surface. Sheets are also moved through the presses with the use of impression cylinders.
Each color of ink used in the offset printing process necessitates the creation of distinct plates and blanket rollers.
For varied run lengths and substrate requirements, numerous variations of presses, plates, and inks are employed. Some publishing houses, for example, may print millions of copies of a magazine. Other printers might print 250 huge sheets to be folded into multi-page pamphlets.