spaceSpace and Physics

University Discovers Its Library Books Hold A Deadly Secret


Tom Hale

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist

Fairly understandably, the librarians have since moved the poison books into a specialized ventilated cabinet. Matteo Provendola/Shutterstock

Poison-laced library books sound like part of a murder mystery plot, or perhaps an elaborate plan to get out of doing college work, but they are just another day's work for some scientists in Denmark. 

Researchers from the University of Southern Denmark have recently uncovered that some of the 16th- and 17th-century books in their library collection held a deadly secret. Using a high-energy X-ray imaging technique, they discovered that the covers of some volumes were made using a green pigment laced with arsenic.


The analysis of three 16th- and 17th-century books showed that the covers were made out of recycled medieval manuscript fragments, as is quite common among certain books from this time. The researchers wanted to see if it was possible to read and identify the original Latin texts. However, the text was obscured by a thick layer of green paint, so they headed to the lab and used a technique known as X-ray fluorescence analysis (micro-XRF) to peer through and see what was underneath. 

Much to their surprise, the analysis inadvertently revealed that the green paint was, in fact, arsenic.  More precisely, they believe the arsenic-containing pigment might be either “Paris green,” which is copper(II) acetate triarsenite, or “emerald green,” also known as copper(II) acetoarsenite.

Arsenic is particularly dangerous because its toxicity doesn’t diminish over time – even after centuries have passed. If elevated concentrations of this stuff end up in your body, it can lead to diarrhea, vomiting blood, blood in the urine, cramping muscles, hair loss, stomach pain, and more convulsions.

Writing for The Conversation, the researchers explain: “This chemical element is among the most toxic substances in the world and exposure may lead to various symptoms of poisoning, the development of cancer and even death.”


Despite its toxic properties, arsenic was widely used in paints and dyes throughout the 19th century. As such, it’s common to find it present in a high number of old paintings, decorations, wallpaper, and textiles. However, the researchers actually believe that arsenic was not chosen for the aesthetic value, in this case.

“In the case of our books, the pigment wasn’t used for aesthetic purposes, making up a lower level of the cover. A plausible explanation for the application – possibly in the 19th century – of Paris green on old books could be to protect them against insects and vermin,” the researchers said.

Fairly understandably, the librarians have since moved the poison books into a specialized ventilated cabinet and hope to digitize the full volume to minimize physical contact in the future.


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