Application of gamma irradiation for the decontamination of historical glass plate photographic negatives

Abstract Ionizing radiation is an effective method for fungal decontamination of photographic heritage materials; however, its application to glass plate negatives may induce optical darkening due to radiation-induced defects in the glass matrix. This study investigates the influence of temperature during gamma irradiation and the potential of UVB light exposure as a non-thermal bleaching strategy. Historical glass plate negatives were irradiated at 6 kGy under room temperature and dry-ice cooling, while common soda–lime–silica glass samples were used as analogues to quantify optical changes. Low-temperature processing mitigated color alterations without affecting decontamination efficacy, whereas UVB exposure promoted partial recovery of transparency in a dose-dependent manner. The combined approach offers a viable strategy for balancing biocidal effectiveness and optical preservation in glass-based photographic heritage.