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Innovations: Xerography

Xerography is a form of copying invented by American Chester Carlson in 1937. Carlson based his method on the property of some materials to increase their ability to conduct electricity when exposed to light (known as photo-conductivity). The xerographic process exposes a photosensitive surface to light reflected through or from the image to be copied. Next the surface is dusted with a dry powder developer that adheres to the charged areas creating a copy of the image. The copy is then transferred to paper and fixed with heat. Carlson's process reproduced black and white images well, but not images, such as photographs, with any shading. Ken Metcalfe and Bob Wright of the Defence Standards Laboratory (formerly the Munitions Supply Laboratory) in Adelaide studied xerography to adapt it for industrial and military use. In 1952 they began to use liquid developers which, because they contained more pigment particles than the dry developers, allowed copying of images containing continuous tones. Metcalfe and Wright's invention allowed the development of colour copying by overprinting consecutive images using different coloured liquid developers.

A success that everyone copied
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