Back Home	Seminar on Records and Archives in Society
Course This Week Past Readings History Archives Projects	Silvia Hansman, HIST 0647, Spring1999 Owen David,"Copies in seconds: a Popular History of Photocopying", Atlantic Monthly, February 1986, 64-73. How Photocopying works... ..."Every photocopier that uses ordinary paper employs some version of the basic xerographic technology embodied in the Haloid XeroX 914. At the heart of this technology is a specially treated surface, usually in the shape of a cylinder, that is known as the photoreceptor. In the 914 the photoreceptor was made of the element selenium. Like a balloon that has been rubbed against a wool sweater on a cold day, selenium is capable of holding an electrical charge. Unlike a balloon, selenium is capable of holding this charge only in the dark. If you shine a light on a charged piece of selenium, the charge will vanish from every part that is illuminated. If you shine the light on a printed page so that an image of the page is projected onto a charged selenium drum, the drum will retain its charge in those places where no light falls (that is, in those places corresponding to the dark ink on the page) and lose it everywhere else. If you then sprinkle the drum with an oppositely charged powdered ink, the ink will stick to the charged parts of the selenium surface, in the same way that house dust sticks to a staticky balloon. This produces on the surface of the drum an exact mirror image of the original printed page. The drum rolls over a piece of paper, transferring the image to it. The copy is made permanent in a device called a fuser, a small heater that melts the powdered ink and binds it to the page..." Back to review