Assuming that you don’t want to poison someone close to you with a gift, you’ll want to be very careful when selecting older books with green covers.

And if you do want to poison someone with a gift, well…I guess this article is for you, too (but we definitely don’t advise this course of action).

Winterthur Poison Book Project might have begun with one green tome and a curious mind, but so far, they’ve found 101 books tainted with arsenic just floating around in the world.

It’s down to a pigment called “emerald green,” which is made from copper acetoarsenite. Discovered in 1808 and manufactured as a pigment in 1814, it was used to color cloth book bindings and also as an insecticide.

The color was extremely popular in both Britain and America in the 1850s, says Melissa Tedone, Conservator and Lab Head for Library Materials Conservation at Winterthur Museum, Garden, & Library.

“These bindings are very common in libraries and private collections.”

The book that began her interest in the subject was an 1857 copy of Rustic Adornments for Homes and Taste, which had a “black, waxy excretion on the surface” and color that was “flaking off really easily.”

Analysis with X-ray fluorescence and Raman spectroscopy revealed the presence of arsenic.

If you work with older books on a regular basis, you should wear nitrile gloves and wipe down surfaces they come into contact with using a disposable cloth – because arsenic poisoning is quite serious.

Short-term symptoms include nausea, diarrhea, and numb and tingling extremities. Long-term exposure can induce skin lesions, cancer, and death.

So double check those books you’ve been handed down, friends.

They might be gathering more than dust.