INVENTOR CHESTER F. CARLSON re-creates the experiment that marked the advent of xerography. The original machine never worked well, but it provided the technological prototype for today's photocopiers. 

The term "xerography," the use of photoelectric phenomena to transfer an image from one sheet of paper to another, comes from the Greek words for "dry" and "writing." Chester F. Carlson, a New York City patent attorney who had studied chemistry at the California Institute of Technology, first demonstrated this technique 58 years ago in a makeshift laboratory above a bar in Astoria, Queens, N.Y. 

Over the next six years, more than 20 companies turned down Carlson's proposals to develop the technology. In 1944 Battelle Memorial Institute, a nonprofit research organization, entered into a royalty-sharing arrangement with Carlson. Battelle eventually signed a development contract in 1947 with Haloid Company, a Rochester, N.Y., firm that produced photographic paper and later became Xerox Corporation. The first xerographic machine came onto the market in 1949, but it was slow, dirty and hard to use. Not until 1959 did Xerox introduce an office copier, the 914, which became the basis for the current multibillion-dollar industry. 

BIRTH OF XEROGRAPHY occurred on October 22, 1938, in Astoria, Queens, N.Y., when Carlson used the process to print this notation on a glass slide using India ink.

Credit: Xerox Corporation; Barry Ross (drawings) 

PHOTOCOPIER moves a document from the handler to the glass platen (not shown), where the pattern of the image is projected by lamps, mirrors and lenses onto a photoreceptor belt (or drum). The electrostatic charge on the belt fades in areas receiving light from the projected image. Magnetic rollers brush the belt with dry ink (toner), which because of its static charge clings to the image area on the belt. A sheet of copy paper approaching the belt is also given a static charge sufficiently strong to draw the image pattern in the toner away from the belt. Rollers then apply heat and pressure to fuse the toner image into place. For color copying, a multistep process is used, which scans the image through color filters and then applies separate toners for magenta, cyan, yellow and black.

Credit: Xerox Corporation; Barry Ross (drawings) 

DRY COPYING exploits the principles that materials with opposite electrical charges attract one another and that some materials conduct electricity better after exposure to light. In the basic xerography process, a photoconductive surface receives a positive electrical charge (a). An image is then exposed on the surface; because the illuminated sections (the nonimage areas) become more conductive, their charge dissipates (b). Negatively charged powder spread over the surface adheres through electrostatic attraction to the positively charged image area (c). A piece of paper is then given a positive charge (d) and placed over the surface, where it attracts the negatively charged powder (e). Finally, heat fuses the image as etched in powder to the paper (f).