Bruce Fowler, Class of '66 -I do not recall the name of the beast, if ever I knew it. We used them when I was in graduate school and then in the early years of paid work to make viewgraphs. The machine used some form of thermographic process. The ink on the page, being dark, had greater heat capacity than the paper. One covered the page of original composition with a sheet to be transferred to. These transfer sheets were relatively flimsy and came in paper or plastic (transparent) versions. My experience was primarily with the latter since Xerox machines were already in early diffusion. The combination of original and transfer were fed into a slot where they were taken into the bowels of the machine where the two were heated appropriately and the inked information on the original was transferred. Proper calibration was needed to assure contrast separation.
I had little experience with this technology for copying, primarily using to make viewgraphs. Their use was limited to small meetings of a singular instance. For larger meetings or several instances, more robust media was necessary, in which case the options were photographic viewgraphs - viewgraphs made using photographic means, or 35mm slides.
Another bit of memorabilia derives from the requirements on the ink used on the original composition. Since "quick and dirty" viewgraphs tended to be made by hand in those days - the alternative was to pay for a commercial artistic technician to make them - the preferred method of inking was to use a Rapidiograph pen with India ink. Since I had little call to compose engineering drawings, this was about my only use of such an instrument outside of note taking in graduate school.
From Wikipedia
Thermo-Fax (very often called Thermofax) is 3M's trademarked name for a photocopying technology which it 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 what was contained in the copy paper. A thin sheet of heat sensitive copy paper was placed on the original document to be copied, and exposed to infrared energy. Where the image on the original contained carbon, the image absorbed the infrared energy and was heated. The heated image then transferred heat to the heat sensitive paper producing a blackened copy image of the original.
The Thermofax process was temperamental. The coated paper tended to curl, and being heat-sensitive, copies were not archival. The darkness setting was tricky to adjust, and drifted as the machine warmed up. Copy darkness often varied across a page, some portions of the text being too light and others too dark. Since the heat absorption of ink does not necessarily correlate with its visible appearance, there were occasional idiosyncrasies; some inks that looked nearly black to the eye might not copy at all, and an exposure setting that worked well for some originals might require a change to make usable copies with another.