Acetic acid detection and cinematographic archives

The preservation of cultural heritage collections is directly and indirectly influenced by environmental conditions (microclimate and air pollution). While monitoring microclimate conditions has become a common practice and is regulated by standards and guidelines, the practice of measuring gaseous pollutant concentrations (organic and inorganic chemical compounds) in indoor spaces housing collections is still poorly carried out. A comprehensive review of the scientific literature conducted by the authors over the 1990-2021 period has evidenced that acetic acid is the primary organic air pollutant monitored in indoor spaces housing collections. We have identified 22 scientific articles where acetic acid was monitored in 32 case studies worldwide belonging to the category of: museums/galleries (15), book archives/libraries (8), worship places (7), and palaces/castles (2). Incredibly we have found that acetic acid monitoring was never conducted in cinematographic archives, although it is well-known that cellulose di- and tri-acetate support of motion picture films can be affected by Vinegar Syndrome, responsible for the emission of acetic acid and triggered by the same chemical compound. It was found that, among the instruments employed for acetic acid detection (both active and passive samplers), the only direct-reading instrument used in literature was the Gastec dosimeter tube; all other methods were based on laboratory analysis (e.g., liquid, gas or ion chromatography) of samples collected after in situ exposure (e.g., charcoal filters, silica gel or Tenax TA tubes, Radiello air samplers, Palmes tubes, and samplers by Swedish Environmental Institute and Norwegian Institute for Air Research). Devices commonly used by film archivists were never mentioned. For this reason, this contribution will present these devices and their use in cinematographic archives. In fact, acetate films are traditionally inspected by film archivists through the deployment inside the film can of dye-coated paper strips, whose reading is based on color change in relation to pH change, i.e., to the emission of acetic acid by film deterioration. There are two manufacturers of these strips: Acid Detection Strips® that are produced by the Image Permanence Institute and Danchek Strips® that are commercialized by Dancan Cine Film Service S.L. The former employed worldwide, the latter mostly in Europe. Ad hoc laboratory test was conducted to compare the performance of these strips and to explore methods for quantifying the color change readings. In addition, some investigation performed by the authors in European film archives (in quarantine and long-term storage rooms) will be presented and discussed. Although measuring acetic acid concentration is not a common research topic, this contribution has brought together the existing literature and completed the framework of current technologies employed in the field of preventive conservation, especially in cinematographic archives.