Fungal biosorption of silver particles on 20th-century photographic documents

摘要

Microbial deterioration is a common problem in photographic collections and is considered a major cause of loss of documents. However, few studies so far have been addressed to biological damage on these materials. Several species of naturally occurring fungi can cause infections on the gelatin-silver emulsion of both positive and negative photographic material, producing defacement and loss of mechanical and aesthetical properties of the objects. In this study a particular phenomenon, spontaneouslycaused by fungi on 20th-century photographic films and positive supports, was documented by means of variable pressure scanning electron microscopy (VP-SEM) combined with electronic dispersion spectroscopy (EDS). This technique allowed the observation ofentire, unaltered films without metallisation thus with a not invasive approach. The ability of some fungi to alter the distribution of silver crystals in the gelatin emulsion was described thanks to a backscattered electrons detector that showed differences in the atomic number of the visualised objects, giving rise to an appreciable contrast in case of different chemical composition.