Byne’s decay on the d’Orbigny’s foraminifera collection at the MNHN, Paris: from the collection assessment to the reproduction of damage by artificial ageing

Alcide Dessalines d’Orbigny (1802–1857) was a micropalaeontology pioneer and his foraminifera collection, housed at the National Museum of Natural History, Paris, is undergoing Byne’s decay. This work was undertaken to evaluate the extent of damage and to better understand when it happened and why. Taking advantage of the E-ReColNat pictures taken of the collection in 2016, a semi-quantitative approach enabled us to estimate that approximately 25% of the specimens are severely affected and are no longer recognisable. The decay is related to the storage materials such as paper, cotton wool and cork used during the 19th century that emit volatile organic compounds (VOCs). Degradation products were identified by Raman spectrometry, thus highlighting major occurrence of the metastable tetragonal calcium formate [β-Ca(HCOO)2]. Orthorhombic calcium formate [α-Ca(HCOO)2] was also detected, yet in much lesser amounts, although it is expected to be more stable than its tetragonal polymorph. Magnesium formate dihydrate [Mg(HCOO)2∙2H2O] and calcium lactate pentahydrate [Ca(CH3CH-OH-COO)2∙5H2O] are also present as minor phases. The fact that no acetate or mixed acetate/formate salt was detected remains particularly puzzling, knowing that acetic acid is a major VOC emitted by cellulosic materials. The study of archival accounts indicates that the decay had already started at the beginning of the 20th century and spread afterwards. It also shows that the collection was stored in several places that presented both high humidity conditions and temperature fluctuations. Taking advantage of these considerations, an artificial ageing experiment was designed to reproduce the decay on newly acquired palaeontological material.