Researchers discovered three poisonous books in a university library in Denmark while they were doing archiving work of finding text hidden within covers of old books.

The books were determined to be coated in arsenic. What was the purpose of covering them with paint that was laced with the deadly poison?

Books Coated In Poison Discovered

In a post on The Conversation, the University of Southern Denmark's Jakob Povl Holck and Kaare Lund Rasmussen narrated how methodical archiving work resulted in the discovery of three poisonous books.

Holck and Rasmussen were analyzing the books because library archivists determined that their covers were made from recycled materials, namely fragments of medieval manuscripts such as copies of Roman and canonical law. European bookbinders from the 16th and 17th century used to place fragments within bindings to improve the strength of the bases of books but for modern archivists, they may be treasures.

According to Rasmussen, after the Danish Reformation in 1536, many Catholic books were destroyed. However, some of the parchments survived when they were used to rebind books, and they are now waiting to be discovered.

Holck and Rasmussen were attempting to read the Latin text in the bindings of the three books but were unable to because of a thick layer of green paint that made it impossible to identify them. The researchers decided to use X-ray fluorescence analysis, or micro-XRF, to try to discern the ink of the text that what was beneath the paint.

The scanning technique revealed a surprising discovery. The paint contained arsenic, a highly toxic and naturally occurring substance, exposure to which results in symptoms such as intestine and lung irritation, stomach ache, nausea diarrhea, skin lesions, and may lead to death.

Why Were The Books Poisonous?

It is easy to imagine the poisonous books being used for murderous purposes, but the real reason why they were coated in arsenic is actually a practical one.

The paint that was used on the books was called Paris green, and it was also used in paintings in Europe in the early 19th century. This means that many pieces in museums today also contain arsenic. The painters stopped using Paris green in the second half of the century, but it continued to find other applications.

In the case of the poisonous books, it was evident that the paint was not used for aesthetic purposes because only a portion of the covers was coated. The researchers believe that the books were painted with Paris green to protect them from being eaten by insects and vermin.

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