Thickness Calculation of Pigment Layers and Gold Leaves Using <scp>XRF</scp> and <scp>MA</scp> ‐ <scp>XRF</scp> Data

ABSTRACT In this work, XRF and MA‐XRF data were used to estimate the thickness of Chromium Oxide (Cr₂O₃) pigment and gold leaf applied over Lead White (2PbCO 3 .Pb(OH) 2 ). The thickness determination was based on the differential attenuation of the Pb‐Lα and Pb‐Lβ characteristic X‐rays, which allows correlating the overlying material layer with the Pb(Lα/Lβ) ratio. The analytical development of the equations relating thickness to this ratio involves parameters that are difficult to determine, such as the attenuation coefficient of the material for the incident energy of the X‐ray tube. To handle this limitation, XRF spectra were modeled under realistic experimental conditions, allowing the generation of data for different thicknesses of Chromium Oxide pigment and gold leaf. Simulated XRF spectra were used to construct calibration curves of Pb(Lα/Lβ) versus d (thickness), which were subsequently applied to experimental XRF and MA‐XRF data. The thicknesses estimated from the calibration curves were compared with those obtained from stratigraphic cross‐sections by Optical Microscopy and Scanning Electron Microscopy. The proposed methodology also enabled the generation of topographic images from MA‐XRF data, showing the distribution of Chromium Oxide pigment and gold leaf applied over Lead White.