Environment-induced risk assessment as a preventive conservation strategy for an effective long-term management of safety cinematographic archives

The primary challenge faced by cinematographic archives preserving cellulose acetate motion picture films is managing the onset and evolution of Vinegar Syndrome, a chemical deterioration process where acetyl groups undergo hydrolysis, releasing acetic acid and triggering an autocatalytic chain reaction. While standards and guidelines recommend maintaining low temperature and relative humidity in storage to slow this process and ensure long-term film stability, in archives the adoption of these measures is often constrained due to limited resources. A review of the scientific literature highlighted that tools developed for the monitoring of Vinegar Syndrome have limitations. Archivists currently rely on visual inspection and on Acid Detection (AD) Strips, which change colour based on acetic acid concentration in the air within the film can. The evaluation is based on comparing the strip colour with a discrete scale affecting accurateness. Studies were conducted to objectively evaluate the Vinegar Syndrome progress by calculating the Degree of Substitution (DS), that represents the number of acetyl groups per anhydro-glucose unit in cellulose acetate polymer. As hydrolytic deacetylation advances, the DS tends to decrease. This research aims to identify an objective approach to monitor Vinegar Syndrome in cellulose acetate film archives. A relationship between microclimate storage conditions, acetic acid emission and film DS was investigated. The Cineteca Nazionale - Centro Sperimentale di Cinematografia (Italian National Film Archive) and the Arquivo Nacional das Imagens em Movimento - Cinemateca Portuguesa (Portuguese National Film Archive) were selected as case studies. Thermo-hygrometric observations collected at the two film archives over many years were used to characterize microclimate. Existing dose-response relationships and damage functions were used to estimate chemical and mechanical climate-induced risks. Then, an empirical relationship between colorimetric measurements of AD Strips and acetic acid concentrations was estimated through laboratory tests to provide an objective film hierarchical classification in real case studies. Finally, DS was derived using portable Attenuated Total Reflection (ATR) Fourier-Transform Infrared (FT-IR) spectroscopy to assess the chemical state of film support. A database including film metadata, ATR FT-IR spectra, strip measures, and additional information was structured to be used as baseline dataset to conduct analysis. It was found that no consistent relationship between acetic acid emission and DS value was identified, complicating DS’s reliability as a standalone marker of Vinegar Syndrome evolution. In conclusion, this research advances current Vinegar Syndrome monitoring procedures for archival cellulose acetate film collections, aiming to improve early-warning detection. The approach was successfully tested in two cinematographic archives and applied by film archivists and conservators.