Photocopiers

Few inventions have transformed office life as much as ‘Xerography’. Before photocopiers came on the market, if you wanted a copy of a document you had three alternates: copy it out on a typewriter or by hand, have it photographed, or take it to a printer. The first was long-winded, the second and third costly and the third also useless if you only wanted a single copy.

American physicist Chester Carlson worked on the answer to this problem in the 1930s. He devised a process in which an electrostatic charge is induces on a surface, which varies the charge is induced on a surface. Light from the original is reflected on to the surface, which varies the charge. When the ‘toner’, a coloured dust, is charged and blown over the surface, it is attracted to the pattern of the image but rejected by the background, resulting in a copy.

Carlson filed a patent for a copying machine in 1939. But it was over ten years before the copier was marketed.