Painting the picture of toxic pigments in Canadian natural history collections

Abstract Victorian paper-wrapped microscope slides produced in Canada were examined to assess health risks and handling requirements associated with arsenic and heavy-metal-based pigments. A subset of slides, including one unwrapped control, was analysed using portable X-ray fluorescence. Arsenic was detected at low levels across most samples, consistent with its use as a glass clarifying agent. Two green wrappers showed elevated Cu–As signals consistent with an arsenical pigment, most plausibly emerald green, while other slides exhibited combinations of heavy metals associated with historical pigments and paper fillers. These results highlight the chemical heterogeneity of 19th-century decorative papers and the interpretive limitations of pXRF when analysing layered, composite materials. Additionally, visually similar materials are found to differ in composition, reinforcing the need for object-specific analysis within historic collections. The historical usage of these pigments is discussed, particularly the arsenical compounds, with a focus on their occurrence in Canadian collections.