If you’re like me, not a day goes by that you don’t either photocopy, receive a fax, or print on a laser printer. In each case you’re using xerography (“dry writing”), one of the most remarkable inventions of the 20th century–and a technology we might not have if not for the dogged perseverance of its inventor, Chester Carlson.
David Owen writes about the history of xerography in the current issue of Smithsonian Magazine.
James Watt of steam-engine fame invented the first mechanical copier in 1780. Users wrote the document they wanted to copy with special ink, then used the press to press a moistened sheet of translucent paper against the inked surface. Some ink would penetrate the translucent paper, which could then be read from the back.
3M’s 1950 Thermo-Fax shone infrared light through an original document onto a sheet of special paper coated with heat-sensitive chemicals. Other chemical-based forms of copying followed. All resulted in copies that smelled funny, faded or turned brown, or kept trying to curl up–or all three.
Chester Carlson, born poor in Seattle in 1906, decided in high school the best way to make something of himself was to invent something useful. After earning a physics degree from CalTech, he was hired in 1930 by Bell Labs in New York City as a research engineer. In 1936, while taking night classes at New York Law School and copying by hand long passages from library law books he couldn’t afford to buy, he began to think about the need for a method of making copies of existing documents–and came up with an idea based on photoconductivity.
A photoconductive material conducts electricity better when light is shining on it. Carlson’s notion was to find a material that was an insulator in the dark and a conductor in the light, apply a thin layer of it to an electrically grounded metal plate, and then, in the dark, to apply a uniform static electric charge to the coated surface. Projecting an image of a printed page onto that surface would change the conductivity of the coating, causing the charge to drain away from the illuminated areas, while the dark areas, corresponding to the text on the page, to remain charged. The plate could then be dusted with an oppositely-charged powder, which would be attracted to the charged areas, forming a visible, reversed image of the original. The powder could then be transferred to a clean sheet of paper and fused onto it to make a copy.
Carlson applied for a patent on October 18, 1937–but it took years for his idea to become reality.
Sulfur has photoconductive properties, but Carlson’s first kitchen experiments succeeded only in annoying his wife. In 1938 he set up a tiny laboratory, and hired unemployed Austrian physicist Otto Kornei as his assistant. On October 22, 1938, Kornei wrote “10.-22. -38 ASTORIA” on a glass microscope slide, then turned out the lights and rubbed his handkerchief over a sulfur-coated plate to give it static charge. He placed the slide face down on the plate and shone a bright light on it for a few seconds. Then he turned off the lamp, removed the slide, and dusted the plate with powder. The letters stood out clearly. Carlson pressed a piece of wax paper against the image so. Some of the powder stuck to the paper–and produced the world’s first xerographic copy (now in the Smithsonian).
Carlson spent the next six years trying to interest someone in his invention. More than 20 companies turned him down, including IBM, General Electric, Eastman Kodak and RCA. Finally, in 1944, a small non-profit R&D organization called the Battelle Memorial Institute invested a small amount. In 1947 a photographic company called Haloid paid Battelle $10,000 for a one-year license to produce a copier based on Carlson’s work. That copier, the 1949 Model A, required dozens of manual operations–nobody wanted it. But 10 years (and millions of dollars) later, Haloid (soon to become Xerox) produced the Model 914, which offered one-button copying.
Carlson worried that no one would ever need to make even a hundred copies a day–the minimum number he though was required for commercial success. But the first companies to get 914s promptly began turning out 3,000 to 4,000 copies a day. And the numbers have kept going up. In 1955, the entire world only made about 20 million copies. In 1964 the world made 9.5 billion copies. By 1984, the number was 550 billion. This year, the world will produce more than three trillion xerographic copies and laser-printed pages–around 500 for every person on the planet.
Not bad for an invention nobody wanted.
