Pigment identification by scanning µ-XRF/µ-XRD

Amongst the techniques employed for pigment identification on art objects such as paintings or painted decorations in historical documents or artefacts, X-ray fluorescence analysis (XRF), Scanning Electron Microscopy with Energy-dispersive X-ray detection (SEM-EDX), Color Spectroscopy and other are frequently used. For more specific pigment identification however, the use of X-ray diffraction and RAMAN spectroscopy is required. While the former method is based on the identification of crystalline materials present, the latter uses the vibrational fingerprint of the compounds present to identify coloured materials with high specificity. However, in RAMAN spectroscopy, in many cases, these vibrational fingerprints are obscured from view due to the presence of a very strong fluorescent background in the spectra. Especially when complex mixtures of small grains of (coloured) inorganic pigments are to be characterized while being present in a matrix of one or more binding media, obtaining clear RAMAN fingerprint data is challenging and sometimes very difficult. The focussed visual or near-infrared laser beams that are employed for Raman spectroscopy also deposit considerable heat in the investigated materials. In order to compare the specificity and ease of use of (scanning) m-XRD with that of µ-RAMAN spectroscopy, the pigments used in a painted decorative border on one folio of a 16th centur