xerography

Dry, electrostatic method of producing images, without the use of negatives or sensitized paper, invented in the USA by Chester Carlson in 1938 and applied in the Xerox photocopier.

An image of the document to be copied is projected on to an electrostatically charged photo-conductive plate. The charge remains only in the areas corresponding to its image. The latent image on the plate is then developed by contact with ink powder, which adheres only to the image, and is then usually transferred to ordinary paper or some other flat surface, and quickly heated to form a permanent print.

Applications include document copying, enlarging from microfilm, preparing printing masters for offset litho printing and dyeline machines, making X-ray pictures, and printing high-speed computer output.