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Blame the paper itself. Old fax machines used thermal paper coated with a colorless dye and a developer that reacted to heat to form the printed image. That reaction is not permanent: it slowly runs in reverse, so the print fades. Meanwhile the paper yellows as its cellulose oxidizes. Photocopying old thermal faxes onto plain paper is the standard way to save them.
| Coating layer | What it does | What goes wrong |
|---|---|---|
| Leuco dye | Colorless until heated; forms the black image when the print head warms it | The colored form slowly reverts, so the image washes out |
| Developer (bisphenol compounds) | Reacts with the dye to trigger the color change | Migrates and degrades; plastic sleeves accelerate the loss |
| Base paper | Thin, smooth roll paper that feeds through the machine | Oxidizes and yellows with age, heat, and light |
Speed and simplicity. Thermal fax machines had no ribbon, no ink, and no toner: a row of tiny heating elements pressed against the paper turned the image on wherever it touched. Offices loved it because the machine had almost nothing to run dry. The tradeoff was baked in from the start: the "ink" was a chemical state of the paper itself, not a pigment sitting on top of it. Anything that disturbed the chemistry: heat, sunlight, humidity, friction, solvents, even the plasticizers in vinyl sheet protectors, would blur, darken, or bleach the print.
Because the color-forming reaction reverses on its own. The dye stays in its colored form only while the chemistry holds; over time it drifts back toward colorless. Heat and light speed this up, but it happens in the dark too, just slower. This is why a fax filed in 1998 can come out of a folder in 2026 looking like a blank, yellowed sheet. Archivists noticed the problem early: a 1993 New Scientist report described libraries and businesses discovering that their thermal-fax records were quietly self-erasing, which is why archives have long treated thermal prints as temporary media.
That is a different chemistry problem. Paper is mostly cellulose, and cheaper thermal rolls contain lignin and acidic residues. Oxidation breaks the cellulose chains down, producing colored byproducts: the familiar tea-stain yellow of old paperbacks. Heat, humidity, and acidic surroundings accelerate it, which is why faxes stored in attics or near radiators yellow fastest. The two processes run in parallel, so an old fax is fighting decay on two fronts at once: the image dissolving and the sheet discoloring beneath it.
Barely. Modern fax machines print with ink or toner on ordinary paper, and online faxing skips paper at the sending end entirely: the document travels as a digital file and lands as a plain-paper printout at the recipient's machine. LetterAgent sends faxes from your AI assistant with a per-fax quote, the page count verified, and one payment before anything is sent, to US and Canadian fax numbers. Fax is available in testing while activation is in progress, so it is described as in testing rather than guaranteed.
Ready to fax it? Fax with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is sent.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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