Photocopying machine, also called Photocopier, any device for producing copies of text or graphic material by the use of light, heat, chemicals, or electrostatic charges. The need for a process other than wet photographic reproduction for copying documents stimulated the invention of various techniques, notably the diffusion-transfer and dye-line processes, during the early 1950s. In the diffusion-transfer process a master copy is made on a translucent sheet, which is placed on light-sensitized negative paper and exposed to light. The negative is then placed in contact with a sheet of positive transfer paper and fed into a developer. When the two sheets are peeled apart, the image is transferred to the positive paper. The dye-line process also requires a translucent original but only one sheet of sensitized paper. This process uses ammonia fumes rather than liquid to develop the image, obviating problems of paper shrinkage.