Characterization of iron oxide-based pigments by synchrotron-based micro X-ray diffraction

The characterization of iron in microsamples by conventional X-ray diffraction is difficult due to its low concentration in thin layers and its low reflecting power relative to other phases. Synchrotron radiation can provide unique information because of high intensity, sample penetration, small beam diameter and fast data collection. In this study, micro X-ray diffraction (μ-XRD) data were obtained of two samples taken from wall paintings at San Agustinʹs Church in Cordoba. Crystalline iron phases such as goethite, lepidocrocite and hematite in the cross-section of the painting thin layers were identified, with a good spatial resolution. Conventional XRD only detected hydrocerussite and cerussite rather than the full range of iron phases found in the μ-XRD experiments.