Study of the pigments elementary chemical composition of a painting in process of attribution to Gainsborough employing a portable X-rays fluorescence system

The investigated painting, named as “The woodman” by its owners, is in process of authenticity verification as a Thomas Gainsborough (XVIII century) painting and is under investigation at the Laboratory of Conservation Science (LACICOR), CECOR/EBA/UFMG. The authentication process is still in course. The measurements were carried out in the place where the painting was on custody, with a portable X-rays fluorescence (XRF) system constituted of a X-rays tube with Ag anode, a Si-PIN diode detector, nuclear electronic chain and a specially designed mechanical system for the detector and X-rays tube positioning, that enables angular and XYZ movements of the excitation-detection system. The employed voltage and current intensity of the X-rays tube were 17 kV and 3 μA, respectively. The time of acquisition for each measurement was 500 s. XRF spectra were analyzed using the AXIL-WinQXAS software. Three measurements in each of the following regions of the painting were done: face, leaves, arm, sky and firewood. The carried out analysis indicated the following pigments: White (lead white and calcium sulfate, identified by the elements Pb, Ca and S), Blue (Prussian blue, identified by the key element Fe), Red (Vermilion, identified by the elements Hg and S) and Brown (mixture of Fe and Mn oxides, identified by the elements Fe and Mn). Elements belonging to modern pigments (after XVIII century) corresponding to the same colors were absent in the analyzed spectra.