Rapid identification of cellulose nitrate and cellulose acetate film in historic photograph collections

Abstract Cellulose nitrate transparent plastic film was used by photographers and movie filmmakers from its release in the 1880s to the 1950s. The storage of this material is a challenge for cultural institutions because of its instability and hazardous nature, as nitrate is highly flammable and deteriorates over time. Historically, cellulose acetate gradually began to replace cellulose nitrate as it is not flammable. Despite its non-flammable properties, leading to cellulose acetate being called ‘safety’ film, over time it became clear that it also deteriorates in hazardous ways. Identification of cellulose nitrate and cellulose acetate in collections is necessary for preservation and risk management to collections and humans. Both cellulose nitrate and cellulose acetate are found in gallery, library, archive and museum photographic collections. As a result, identification and management of this material might be the responsibility of curators, librarians, archivists, collection managers, registrars or conservators, depending on the institution staffing and structure. Currently, there is no single identification method readily available to heritage institutions that meets the requirements to identify and distinguish between cellulose nitrate and cellulose acetate reliably, non-destructively and rapidly. In this study samples from both the Sydney University Museums and Australian National Maritime Museum collections have been analysed using infrared total reflectance spectroscopy, a novel approach which demonstrates great potential for rapid and non-invasive identification particularly when combined with multivariate statistical analysis methods. Principal component analysis (PCA) allowed for non-subjective data mining and the development of a model which is hoped to be used in the future for predicting sample identification. After calculation of the PCA model, the novel application of the Parsimax orthogonal rotation method potentially provides a means of determining the level of chemical deterioration in the cellulose nitrate film.