Middlesex University researchers make ‘first ever’ discovery of arsenic in Victorian microscope slides

New study recommends guidelines for safe handling of 19th century artefacts in museums and private collections

Middlesex University researchers have discovered, they believe for the first time, the presence of arsenic in Victorian-era ‘papered’ microscope slides.

The research, published last week in the Journal of Cultural Heritage, tested a sample of 27 antique slides and found arsenic present in the decorative paper covering 25 of them. The paper labels were in a variety of colours, although arsenic was only found in those that had green, and some red, pigments.

The study’s authors, Dr Leonardo Pantoja Munoz, a Technical Tutor in Analytical Chemistry, and Dr Huw Jones, Associate Professor of Environmental Chemistry, made the discovery during research into historical pigments. They believe their investigation is the first of its kind and could have implications for how public and private collections of 19th century slides are handled, stored or disposed of.

It is also reminiscent of the Poison Book Project, a research programme to find potentially toxic pigments in bookbinding components. Earlier this year, four books were removed from France’s national library in Paris over concerns their covers may be laced with arsenic. The 19th century volumes, printed in Britain, all are presumed to contain emerald green covers.

Dr Jones said: “Our research highlights a previously unrecognised occupational and environmental hazard associated with historical slides. In our paper, we emphasise the importance of responsible handling, storage, and disposal practices for slides potentially containing arsenic pigments, especially those that are green or red-coloured, to minimise health and environmental risks.”

During the mid-19th century, a practice emerged of attaching colourful decorative paper to glass slides to hold specimens in place and provide written information about the type of specimen and the preparer’s name. At the time, arsenic-containing chemicals were commonly used for a bright emerald pigment to colour paint, wallpaper, book covers, and even sweet wrappers until safer alternatives were found.

“Our research will be of interest to institutions as well as private collectors holding Victorian-era papered slides, as well as anyone with an interest in the history of arsenic and more broadly in toxicology in terms of occupational and environmental hazards."
Dr Leonardo Pantoja Munoz

Dr Pantoja said: "It also adds to recent studies highlighting the presence of arsenic in other items of historical interest, such as 19th century book bindings in library collections.”

The research involved three stages: identifying in laboratory studies the presence of arsenic in slides, conducting an online survey to estimate their prevalence in UK collections, and recommendations on how to mitigate any risk to health.

The researchers used and compared a variety of techniques in laboratories at Middlesex University to determine the presence of arsenic, including X-ray fluorescence, Raman and optical emission spectroscopy to identify the composition of small proportions of the paper wrapping.

Their recommendations for museums and private collectors include encouraging researchers to use digitised examples rather than original slides where possible, certain procedures when handling original emerald green slides such as using gloves at all times and using hard wipeable surfaces when examining slides, routine cleaning of microscopes after use, and ensuring all staff are trained for handling activities.

Dr Pantoja said: “Estimating the true prevalence of arsenic-containing slides across collections is challenging. Most museums haven't analysed their slides for arsenic because this issue hasn't been previously reported.

“Despite these uncertainties, our initial investigation suggests that up to 10% of slides in museum collections might be affected. Considering estimates of historical slides exceed nine million in UK collections alone, this finding warrants further investigation and highlights the importance of safe handling practices in museum and private collections.”

Dr Jones added: “The risk needs to be assessed on a case-by-case basis. Handling one slide is very unlikely to be harmful, but if you are opening up a stored box of 100 you might want to take precautions as you could be inhaling arsenic from dust particles where the paper covers have degraded.

“Based on our preliminary findings, it is appropriate to raise awareness among museum staff, researchers, microscopy societies, and amateur microscopists for the safe handling of these valuable historical artefacts.” 

• The Hidden Arsenic Legacy In Mid-19th Century Papered Microscope Slides is published the Journal of Cultural Heritage. 
• Photo Credit: Dr Leonardo Pantoja Munoz.