Thermofax

Thermo-Fax (very often Thermo fax) is 3M`s trademarked name for a photocopying technology which was introduced in 1950. It was a form of thermographic printing and an example of a dry silver process. It was a significant advance as no chemicals were required, other than those contained in the copy paper itself. A thin sheet of heat sensitive copy.
Found on http://en.wikipedia.org/wiki/Thermofax
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