Preparation Methods and Accessories for the Infrared Spectroscopic Analysis of Multi-Layer Paint Films

Several traditional paint samples were prepared for infrared spectroscopic analysis in a number of different ways. The methods applied include the formation of KBr pellets, squeezing of dissected or multi-layer samples in a diamond cell, embedding in a modern resin, and a new method in which a paint cross-section is embedded in KBr and polished from both sides to obtain a thin layer. Microtoming of a paint cross-section embedded in a modern resin was not successful. The various samples were analysed by infrared spectroscopy to assess the usefulness of these sample preparation techniques in the field of paintings research. The amount of information that can be derived from the infrared spectra obtained appeared optimal for sample preparation methods that allow the application of transmission techniques. The results obtained for specular reflectance techniques were of lesser quality, while no diffuse reflectance spectra could be obtained. The results can best be traced to a specific layer or structure in an inhomogeneous paint system if the layer structure of the sample is left intact, i.e., using specular reflectance of an embedded cross-section or transmission of a thin section obtained by doubly polishing a cross-section embedded in KBr.