Use of a portable EDXRF system for pigment analysis of sculptures and mural paintings

This work it is shown the use of the portable EDXRF system of the Applied Nuclear Physics Laboratory (LFNA) of the State University of Londrina (UEL), for the pigments study of two wood sculptures and mural paintings of the Paroquia Imaculada Conceicao Church, Sao Paulo, SP, Brazil. The portable EDXRF system is constituted of a X-ray tube with Ag anode (operated at 17 kV and 2 μA for the sculptures measurements and at 17 kV and 3 μA for the mural paintings analysis), a Si-PIN detector (FWHM = 221 eV for the 55Fe(Mn) 5.9 keV line), standard nuclear electronic chain for X-ray spectrometry, a 8K multichannel analyser, a HP200LX palm top and a mechanical system for the positioning of detector and X-ray tube, which permits three degrees of freedom for the excitation-detection system movement. The excitation-detection time was 500 s for each measurement. For both sculptures, the analysis of the clothes areas indicated that the brown colour was obtained from a mixture of Fe and Mn oxides based pigments, due to the strong presence of the key elements Fe and Mn. In the analysed mural paintings, the following pigments were indicated due to the measured key elements: pale ochre - Fe hydrated oxide, Mn and Cr oxides, Zn and Ti oxides; blue . Prussian blue (Fe key element); beige . blend of Fe and Cr oxides with white of Zn and Ti oxides; green . hydrated Cr hydroxide or Cr oxide; pale yellow (mixture of Zn and Ti oxides); and red . Fe oxide. (author)