Glass alteration in 19th century glass photographic plates: Potential role in gelatin delamination

The Smithsonian Institution's National Museum of American History houses the largest remaining collection of inter-positive composite glass plate images from the production of Eadweard Muybridge's Animal Locomotion series. These photographs, which are approximately 150 years old, exhibit a wide range of degradation phenomena and products, including alteration of the glass plates. Compositions of both the image-bearing glass plates and support glass panels were obtained through quantitative scanning electron microscope–energy-dispersive spectrometry. Electron imaging of cross-sectioned samples of the image-bearing glass plates reveals a visible sodium-depleted glass alteration layer. Furthermore, electron imaging shows delamination of the image-containing gelatin layer and captures evidence that suggests that interfacial stresses between the glass alteration layer and the unaltered glass contribute to the delamination of this layer along with the overlaid gelatin.