The University of St Andrews' detection tool uses visible near-infrared (vis-NIR) spectroscopy to identify emerald green pigment through its unique "fingerprint" in the visible spectrum.12 The device shines different colors of light onto book bindings and measures the reflected light pattern, with emerald green displaying a distinctive reflectance pattern at 515 nm wavelength that clearly differentiates it from other green pigments.23 This technology was validated against more complex analytical methods including Raman spectroscopy, which identifies emerald green through characteristic bands at specific wavelengths, and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS), which analyzes elemental composition.23

While other institutions have relied on X-ray Fluorescence Spectroscopy (XRF) to detect copper and arsenic in book bindings4, the St Andrews approach offers significant advantages. The portable spectrometer, originally designed to identify minerals in rocks for geological applications, has been repurposed into an affordable, user-friendly tool that requires minimal training and can screen books in "a fraction of a second."13 This accessibility democratizes toxic pigment detection, allowing even small institutions with limited resources to accurately identify hazardous books in their collections without expensive specialized equipment.12

Arsenic-containing pigments were widely used in book bindings during the 19th century, with emerald green (copper acetoarsenite) being particularly prevalent. This vibrant green pigment was applied to bookcloth, paper covers, endpapers, leather onlays, and even textblock edges1. The poisonous substance wasn't limited to 19th-century publications—researchers have discovered arsenic-rich green paint on 16th and 17th-century book covers as well2. While the toxic properties of arsenic were known during the Victorian era, the affordability and popularity of emerald green (also called Paris green) led to its widespread use despite the health risks3.

The dangers posed by these arsenical books are significant for those who handle them regularly. The pigment is extremely friable, meaning it easily flakes off into an invisible dust that can cause irritation to the eyes, nose, and throat, along with potential dizziness, nausea, and more serious health effects with repeated exposure14. The Poison Book Project, started in 2019 at the Winterthur Museum, has confirmed over 100 books containing Paris green across libraries worldwide5. Interestingly, in some cases, the arsenic wasn't just decorative—it may have been deliberately applied to prevent insect damage, essentially functioning as a bookworm repellent6.

Spectroscopic techniques provide distinctive "fingerprints" that reliably identify emerald green in historical artifacts. Vis-NIR spectroscopy reveals emerald green's unique pattern in the 470-565 nm range, characterized by negative values in the second derivative of reflectance and three distinct peaks at 574, 595, and 617 nm1. This pattern clearly differentiates emerald green from other green pigments, creating a reliable identification method. For validation, Raman spectroscopy identifies emerald green through characteristic bands at 951, 539, 492, 371, 242, 217 cm⁻¹ and other specific wavelengths12.

Multiple complementary techniques enhance identification accuracy. SEM-EDS analysis confirms emerald green's presence by detecting its elemental composition, particularly copper and arsenic3. FTIR spectroscopy helps identify not only pigments but also associated organic components like binders and varnishes that might affect degradation patterns4. This multi-analytical approach creates a comprehensive fingerprinting method that allows institutions to rapidly and non-destructively identify potentially toxic books without specialized expertise, making collection safety assessments more accessible to libraries of all sizes3.