Abstract
Microscope slide collections represent extremely valuable depositories of research material in a natural history, forensic, veterinary, and medical context. Unfortunately, most mounting media of these slides deteriorate over time, with the reason for this not yet understood at all. In this study, Raman spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, and different types of light microscopy were used to investigate the ageing behaviour of naturally aged slides from museum collections and the experimentally aged media of Canada balsam and Permount™, representing a natural and a synthetic resin, respectively, with both being based on mixtures of various terpenes. Whereas Canada balsam clearly revealed chemical ageing processes, visible as increasing colouration, Permount™ showed physical deterioration recognisable by the increasing number of cracks, which even often impacted a mounted specimen. Noticeable changes to the chemical and physical properties of these mounting media take decades in the case of Canada balsam but just a few years in the case of Permount™. Our results question whether or not Canada balsam should really be regarded as a mounting medium that lasts for centuries, if its increasing degree of polymerisation can lead to a mount which is no longer restorable.
Highlights
Worldwide, natural history collections, forensic institutes, veterinary institutes, universities, and medical hospitals house millions of microscope slides with entire specimens, body parts of a specimen, or histological sections for both reference and research purposes [1,2,3]
We studied naturally aged microscope slides from different collections and museums with the help of Raman spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, and different types of light microscopy to identify the mounting medium, measure the absorbance, and relate the deterioration artefacts to physicochemical changes during ageing
The mounting media of 12 microscope slide samples from natural history collections were determined using a Raman spectroscopy method previously described by Schmid et al [24]
Summary
Natural history collections, forensic institutes, veterinary institutes, universities, and medical hospitals house millions of microscope slides with entire specimens, body parts of a specimen, or histological sections for both reference and research purposes [1,2,3] Such reference collections are indispensable for the description of new species by comparing them with known species, identifying unknown specimens, for teaching, and for studying diseases and parasites. We studied naturally aged microscope slides from different collections and museums with the help of Raman spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, and different types of light microscopy to identify the mounting medium, measure the absorbance, and relate the deterioration artefacts to physicochemical changes during ageing.
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