Fig. 1: Degraded glass objects of the cultural heritage conserved in atmosphere since their date of production.

Set of two degraded glass objects of the Musée des Arts Décoratifs, Paris, showing the advanced stage of crizzling (stage 4). a, b Degraded glass ewer, inv. 23431 (H. 19 cm). c, d Fragment of a glass support of oil and vinegar flasks, inv. 22,747 (H. ~5 cm). ^©C2RMF, A. Maigret. b and c optical microscopy images showing the formation of small flakes of hydrated glass and their detachment from the surface. e–h SEM images (back-scattered electrons) of the edge of a resin-coated and polished sample of the glass fragment. The alkalies (K, Na) are depleted in the hydrated layer, explaining the contrast on SEM images, but their depletion is partial (Table 1). ^©C2RMF, F. Alloteau. The pink color is due to the atmospheric alteration through the oxidation of manganese in the hydrated layer (solarization phenomenon). The micrometric holes may have been induced by the polishing step, they reveal the mechanical fragility of the hydrated layer and probable submicrometric porosity. Scale bars are b and c 1000 µm, e and g 10 µm, f and h 1 µm. Panels c–e are reproduced with permission from ref. ¹³, Editions Hermann, 2019.