Dual Spectrum thermal paper c. 1964-1970; Thermo fax front printing and back printing (not completely sure of the dates on these, but roughly the late 1950s, the 1960s and early 1970s). Used as copy paper in early copy machines, then as fax paper and later as plot printers and some electronic-whiteboard printers. It continues to be used as fax paper, receipt paper, automatic teller receipts, etc.
Thermal paper is the type most of us know as fax paper, receipt paper or sometimes NCR* although NCR is really carbonless, not thermal. The NCR company and engineers did, however, play a large part in the development of thermal paper along with Texas Instruments, Appleton, IBM and others.
Thermal paper is glossy, slippery/slick feeling stuff that discolors when we use a highlighter and fades faster “than freshman at a keg party” (haha, j/k I overheard this one at the pub and got a good laugh out of it). The backside of early thermal copy paper sometimes has a blue ‘flame’ image with a registered trademark. The flame actually looks more like agave or aloe, but then again I lived in the desert for 10 years. Funny enough, there is another version of this paper with a saguaro image on the backside. I’m still looking into that. If anyone knows about this – please comment!
An important aspect of fax paper and any other thermal paper is that it really does have a tendency to fade. These papers also react poorly to traditional manila file folders, exposure to light, marking or pressure/rubbing of any kind (i.e. scraping accidentally with another folder, cup or fingernail, etc.). Pull out any of your office files from a few years back (pre-laser fax) and take a peek at your docs. Pull out a thermal receipt from your bank, grocery store or other automated service. Chances are the image is fading, the paper is darkening or yellowing, or the image is otherwise damaged.
The chemical layers in these papers remain active long after they have been filed and stored. I won’t go into the exact chemical make-up of this paper but it might be easiest to say that the paper is coated with developer and a chemical dye. The chemicals are designed to react to heat, which triggers the dye and developer. (As an aside, there is some controversy around the BPAs levels and acceptable exposure).
Suffice to say that if you have something of value printed or copied on thermal paper – transfer it via digital scan, copy, photograph or otherwise because although it may have lasted the last 30 years there is no guarantee it will last another 30. This is probably not going to be your grocery receipts, but it might be a fax copy of your school records, a fax in your office you need to retain for records or other prints. There were also some photo booths and portable ‘fun’ printers in the 90s that used a similar paper.
*NCR is the acronym for the company name National Cash Register, but the acronym came to be used popularly to refer to carbonless copy paper that involves a different process and different chemical from thermal paper.
Appleton. (2011). http://www.appletonideas.com/Appleton/jsps/historytextmiddle.do?langId=&catalogId=239327&storeId=139327
Aaron Fine Chemicals. (2011). http://www.aaronfinechem.com/about.php
Environmental Working Group. (2012). http://www.ewg.org/
Texas Instruments. (2011). www.ti.com/corp/docs/company/history/lowbandwidthtimelinecsis.shtml
NCR. (2011). http://www.ncr.com/about-ncr
And a whole lot of personal experience with fax paper, NCR forms, weird chemical reactions and strange printing papers.