Xerography.

Patented method for document copying. By 1940, Chester F. Carlson had demonstrated his method of electrostatic copying, or “electrophotography” as he called it, on a small scale. With an assistant he hired at his own expense, he developed a sort of kit that he could use to show his process to others. At the heart of his method was a photoconductive layer of sulfur on a zinc plate. The sulfur layer could be electrostatically charged by rubbing it with a silk cloth. Seeking sponsors for further development, Carlson contacted companies such as International Business Machines (IBM), the Charles Bruning Company, and several others without obtaining any definite commitments. In 1944, Carlson contacted the Battelle Institute in Columbus, Ohio, and made a favorable impression with his demonstration.