Xerography

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Xerography (or electrophotography) is a dry photocopying technique invented by Chester Carlson in 1938, for which he was awarded U.S. Patent 2,297,691 on October 6, 1942. Carlson originally called his invention electrophotography. It was later renamed xerography from the Greek roots xeros "dry" and - -graphia "writing" to emphasize that, unlike reproduction techniques then in use such as cyanotype, this process used no liquid chemicals. Although Georg Christoph Lichtenberg invented a dry electrostatic printing process in 1778, Carlson''s innovation combined electrostatic printing with photography. Carlson''s original process was cumbersome, requiring several manual processing steps with flat plates. It was almost 18 years before a fully automated process was developed, the key breakthrough being use of a cylindrical drum coated with selenium instead ofa flat plate. This resulted in the first commercial automatic copier, released by Haloid/Xerox in 1960. Xerography is used in most photocopying machines and in laser and LED printers.