These days, we tend to give arsenic a fair bit of prominence – the element isn’t known as the ‘king of poisons’ for nothing. Its toxicity stems from its similarity to phosphorus, an essential nutrient for life, which allows arsenic to invade and disrupt important chemical reactions in the body. The element is also happy to mix with others, often forming deadly, undetectable powders with no taste or smell.
Yet this versatility is what made arsenic so ubiquitous in a variety of Victorian-era products, from home decor and wallpaper to clothing and books. When combined with copper oxide and lime, it produces an eye-catching compound called copper acetoarsenite, or emerald green.
“At the time, emerald green was the strongest and brightest green dye available and it was a very popular color among consumers,” says Melissa Tedone, conservator at the Winterthur Museum in Delaware. “No alternative dye could even come close to the intensity of the color.”
Toxic emerald green
In bookbinding, its use as a dye allowed arsenic to spread far and wide. Because it was used at a time when manufacturers produced books in large and small-scale bindings using machines, Tedone estimates that up to tens of thousands of books were bound in emerald green between the 1840s and 1860s. (Our understanding of 19th century bookmaking is limited, thanks to closely guarded trade secrets.)
Although a series of accidental arsenic poisonings sparked debate about the substance’s safety towards the end of the era, she continues, manufacturers are unlikely to have quickly abandoned the tint until there was a strong demand.
So in 2019, Tedone and his colleagues began testing hundreds of books from Winterthur and the Library Company of Philadelphia. About half of them contained lead; others revealed different heavy metals, such as chromium and mercury. But just over 10% contained arsenic emerald green – a much greater health risk for librarians, collectors and researchers. This danger is not only due to the toxicity of arsenic, but because the powder tends to flake off easily from a bond and into the air when disturbed.
“Arsenic shift is invisible to the naked eye,” Tedone explains, “so a person handling an arsenic book wouldn’t necessarily see green pigment shift onto their hands or other surfaces.”
Read more: Why arsenic poisoning is more than a murder mystery
Identify pounds of arsenic
In response, the Conservatives launched the Poisoned book project, an “ongoing investigation to explore the materiality of Victorian publishers’ bindings”. They use a number of non-destructive analytical techniques to identify books of arsenic without damaging them: When X-ray fluorescence spectroscopy detects arsenic and copper together, a second method called Raman spectroscopy can confirm the presence of emerald green.
“It’s an important part of cultural heritage work to analyze and better understand the collections that we care about,” says Tedone, chief curator of the Poison Book Project. “However, we absolutely do not want to damage these materials in the name of research!”
More recently, the project has expanded to include crowd-sourced data. Thanks to the work of researchers from more than a dozen other institutions and private collections, 101 pounds of arsenic have so far been identified, Tedone says. To help to the huge company, the Poison Book Project distributes bookmarks with safety warnings and pictures in different emerald green colors. By August, the project had distributed more than 1,500 bookmarks in 49 states and 19 countries around the world.
(Credit: Winterthur Library/Collection of Printed Books and Periodicals)
While anything short of consuming an entire Toxic Tome would lead to a severe case of arsenic poisoning, exposure to copper acetoarsenite the particles can further irritate the eyes, nose and throat. For librarians and researchers, repeated interactions can cause more serious internal symptoms such as dizziness and nausea. For these reasons, if you suspect you’re handling an emerald green bound Victorian book, be sure to wear nitrile gloves, avoid touching your face, and wipe down all surfaces when you’re done. Then consider ask a color swatch bookmark just to be sure!