Non-Invasive Characterisation of Bromoil Prints by External Reflection FTIR Spectroscopy

The bromoil process, developed in 1907, was a photographic technique highly esteemed by pictorialist photographers for its capacity for image manipulation, which aligns its expressiveness with traditional pictorial techniques. Despite the artistic and technical value of bromoils and their prevalence in renowned collections, there is little research on their composition and structural characteristics. This study uses non-invasive external reflection FTIR spectroscopy to characterise 16 bromoil prints dating from the 1920s to 2010. FTIR spectroscopy allowed the discrimination of key components such as cellulose, gelatine, pigments, and oils, elucidating the structural and compositional complexity of bromoil prints. The study presents new perspectives on the traditionally recognised structure of bromoil prints, based on FTIR spectroscopy results along with evidence from microscopic examination, particularly regarding the role of certain strata in their identification. These results suggest a need to reconsider the understanding and characterisation of bromoil prints in relation to the currently available literature. This research also proposes a measurement model adapted to the studied samples and addresses the advantages and limitations found in the different types of equipment used. It thus proposes a key methodology for the identification and provides a source for the physicochemical studies of photographic processes.