Infrared spectrometry can be used to determine the organic structure of an unknown material, including photographic materials such as gelatin and collodion. Diffuse reflectance FTIR can be used as a completely non-destructive technique for characterizing the surface of objects such as photographs. However, reflectance spectra differ from transmission spectra. Collodion and gelatin are easily differentiated, while gelatin and albumen are more difficult to differentiate. A more extensive survey of the range of historic photographic materials is planned.