Thermofax

Thermofax was a thermal copying process developed by the 3M company in the 1950s. It was one of the earliest document copying technologies and was based on infrared light and heat-sensitive paper.

The Thermofax process worked by shining a bright infrared light onto an original document. Dark areas on the original absorbed more infrared radiation and therefore became hotter. This heat was then transferred to a specially coated copy paper, which was chemically treated to darken where it was heated. The resulting copy was a relatively low-resolution, often brownish or slightly blurry image.

While Thermofax machines were faster than mimeographing and other earlier copying methods, the copies produced were not of archival quality and tended to fade over time. Also, the special Thermofax paper was more expensive than plain paper, and only one copy could be made at a time. Due to these limitations, Thermofax technology was eventually superseded by other copying processes, most notably xerography.

Thermofax is now primarily of historical interest, representing an important step in the development of modern photocopying technology. The term "Thermofax" is sometimes used generically, though incorrectly, to refer to any early thermal copying process.