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3M Thermo-Fax
Tool identification

Name of tool: Thermo-Fax
Alternative name: Thermofax
Inventors/Designers: Carl S. Miller
Marketed by: 3M (Minnesota Mining and Manufacturing Company)
Design date: 1940-1945
Marketing date: 1950
Type of application: photocopier

Historical notice

As a doctoral student at the University of Minnesota in the 1940s, chemist Carl S. Miller tried to invent a simple means of reproduction to avoid having to transcribe his notes and the multiple versions of the thesis he was writing. He had noticed that a dead leave lying on the snow left imprints that varied in clarity with the temperature difference between the two surfaces. It was this observation that led him to discover the basic law of thermography, a procedure he patented later that decade. After being hired by the Minnesota Mining and Manufacturing Company (3M), Miller began to conduct research on pigments, while continuing his work to prototype the first copier. As early as 1944, he presented a rudimentary model to 3M directors, who as a result allowed him to focus entirely on the design of a thermal fax machine based on carbon-treated paper. The Thermo-Fax was marketed in 1950 and sold extremely well until the mid 1960s.

Brief list of components

Mechanical belt, infrared lamp, chronometer. Printing materials: paper treated with a carbon-based chemical formula (any surface treated with carbon).

Operating procedure

The Thermo-Fax generated a brownish print that reproduced the approximate grey scale of an original. Carbon paper was placed on the reproduction surface and passed across an opening in the external component of the machine. The mechanical belt then guided the paper towards the infrared lamp housed inside the machine. The dark zones absorbed the heat, while the clear zones reflected it. In this way, the carbon adhered only to those areas exposed to the heat to produce the image. A chronometer would speed up or slow down the rotation of the belt, thus varying the exposure time to the infrared rays.

Effects and functionalities

Brownish print reproducing the approximate grey scale of an original.

Vincent Bonin © 2007 FDL