Learning Resources

Photocopying machine

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.