Selenium Never Forgets

Hugh G. White (G'Raffiti; reprinted with permission)

Lithosphere (April 1993); Fallbrook Gem and Mineral Society, Inc.; Fallbrook, CA

In the mid '30s, Chester Carlson invented a new method of copying images onto paper. Prior to that time, only a wet process similar to photography was used to make copies.

Carlson developed a dry process that transferred powdered ink, called toner, from an optically induced image on a negatively charged transfer device to a piece of positively charged paper. The toner was then heated which melted and fused it onto the paper.

In the process of perfecting his new copying technology, Carlson experimented with belts and plates as the transfer device. Neither of these worked very well. Finally, Carlson set upon the idea of using a coated drum as the transfer device. At first, in an attempt to imitate the photographic process, he used silver compounds to coat the drum. Eventually, Carlson chose selenium as the coating. The process, now known as xerography (from the Greek for "dry writing"), earned Carlson a patent -- and now everyone knows about Xerox copiers.

Later, when Carlson was asked to identify the most difficult part about inventing xerography, he stated that the hardest problem was finding the proper coating. He said, "The primary reason that we settled on selenium is its unique crystal lattice and the way that it retains an electrostatic charge indefinitely. We chose selenium because it truly is the element that never forgets."

The preceding article was published in the April 1993 issue of Lithosphere, the official bulletin of the Fallbrook [California] Gem and Mineral Society, Inc; Richard Busch (Editor).

Permission to reproduce and distribute this material, in whole or in part, for non-commercial purposes, is hereby granted provided the sense or meaning of the material is not changed and the author's notice of copyright is retained.

Last updated: 18 September 2002