Identification of black and white antique photographs via non-destructive microscopic and spectroscopic techniques coupled with chemometric approaches

In this study, we investigated three types of black and white antique photographs, namely salt print, albumen photograph, and silver gelatin photograph, utilizing multiple techniques. Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy and spectroscopic imaging, confocal light and laser microscopy, X-ray Fluorescence (XRF), and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) were employed to characterize these antique photographs, providing structural and chemical information. Chemometric methods including Principal Component Analysis (PCA) and k-means clustering were utilized to analyze the ATR-FTIR spectroscopic imaging data obtained from the surface and cross-sectional samples of the photographs, respectively. Successful differentiation of the three antique photographs and chemical characterization of different layers within each photograph were achieved. These results demonstrate a promising approach for the non-destructive and efficient identification of various photographs with distinct manufacturing processes.