I have heard it said by several insiders at several publishing houses that green books don’t sell. It’s true that you don’t see a whole lot of them, especially when compared with their red and yellow-jacketed cousins. It’s beyond me how one would undertake a rigorous study of this claim, but that’s what makes folk wisdom so great, and what lends it its power.

Another thing that helps propagate an unverifiable truth is a mysterious and dangerous backstory. What if, for instance, green books had been known to kill? Now we’re talking.

And that dangerous possibility has had librarians at the University of Southern Denmark talking as well — owing to the fact that X-ray analysis has revealed that three books in the university’s collection contain arsenic in the paint on their green covers.

Sarah Laskow provides some useful context at Atlas Obscura:

For years, in the 19th century, arsenic was considered dangerous to eat but safe enough to use in other ways, including as dye in postage stamps that were meant to be licked or in green dresses worn to fancy balls. It was regularly used as an ingredient in green paint, to help the color last longer. Now, though, we know that when arsenic is used in paint, it’s still very dangerous. It can form microscopic particles that can make their way into people’s lungs. In some circumstances, arsenic paint can even give off a poisonous gas.

Experts speculate that the books were painted poison green for utilitarian reasons: to ward off insects and other creatures that might nibble at the text. Sales deterrent and bug deterrent? Perhaps more centuries will pass before we know.

So common was arsenic in old textiles that there are even poison books about the dangers of poison books. Back in January, we wrote about one such freak of history:

Shadows from the Walls of Death in a nineteenth-century book comprising pages of wallpaper samples. Innocuous enough, you might think… until you learn each sample is saturated with arsenic. This is not as weird as it might sound — it turns out when arsenic is mixed with copper it can create some mightily pretty pigments, the best-known being Scheele’s Green and Paris Green.

Pair this with urban (suburban, really) legends about green M&Ms, and you begin to shape a whole canon of myths surrounding green dyes.