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Projeto de investigação
DESENVOLVIMENTO DE PADRÕES EM PAPEL PARA A ANÁLISE QUANTITATIVA DE DOCUMENTOS HISTÓRICOS
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Monte Carlo simulation of portable XRF setup: Non-invasive determination of gold leaf thickness in indo-Portuguese panel paintings
Publication . Pessanha, Sofia; Manso, Marta; Antunes, Vanessa; Carvalho, Maria Luisa; Sampaio, J. M.; LIBPhys-UNL; Elsevier
In this work, we present the combined use of in situ X ray Fluorescence spectroscopy and Monte Carlo simulation using PENELOPE code for the completely non-invasive determination of gold leaf thickness in artworks using lead white as mordant. The methodology used is based on the detection of different characteristic lines of Pb in the X ray fluorescence spectra, attenuated trough the gold leaves, and determining the thickness of gilding by comparing their attenuation. Firstly, this methodology was calibrated using model samples of simple stratigraphy, namely pure Au leafs of 1, 2 and 2.5 μm thickness covering a Pb infinitely thick sheet. The modelled X ray setup was then used to study the gilding thickness of three panel paintings belonging to the Museum of Christian Art in Old Goa (India): two paintings, from the 18th century, concerning to the same series but different themes: Our Lady of Sorrows (MoCA1) and Our Lady of Seven Sorrows (MoCA2), and a third painting entitled Monstrance (MoCA3), from the 17th century. These panel paintings were analyzed to understand the differences and similarities between techniques, according to the time/epoch and technique of its manufacture. The obtained values for MoCA2 tend to be slightly lower than for MoCA1, however, the t student test revealed that the differences were not statistically different (p = .37). Regarding the MoCA3 painting, the average thickness was determined to be statistically different (p < .001) and higher than for the other two paintings. These results emphasize the use of different techniques concerning gold leaf beating. In the 17th century painting it was verified the use of a thicker gold leaf while in the group of the 18th century gold leaf was thinner and manufactured with a similar thickness in both paintings. These results are in consonance with the accuracy of leaf beating technology, increasing with the experience acquired during the ages.
New insights into the red and green pigments in the illuminated foral charter of Setubal (1515) by combined use of μ-Raman and X-ray fluorescence spectrometry
Publication . Guerra, Mauro; Carvalho, Maria Luisa; Le Gac, Agnès; Manso, Marta; Mortari, Camila; Longelin, Stephane; Pessanha, Sofia; LIBPhys-UNL; DF – Departamento de Física; DCR - Departamento de Conservação e Restauro; AIP - American Institute of Physics
The richly decorated foral charter attributed by D. Manuel I of Portugal, in 1515, to the village of Setubal, was studied using Energy Dispersive X-ray Fluorescence spectrometry and Raman micro-spectroscopy. An in situ characterization of the pigments used in the production of this masterpiece showed a very different pigment palette choice when compared to other similar Manueline charters. The red and green pigments are particularly puzzling, as the widely used mercury- and copper-based pigments, vermillion and malachite, respectively, were not found in the illuminated frontispiece. Instead, the cheaper lead-based pigment minium was used in the King's flag, while a mixture of copper sulfates was found for the green color, identified by means of micro-Raman spectroscopy. This result led to a new look at the conception that only one Royal workshop existed for the elaboration of Manueline foral charters.
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Fundação para a Ciência e a Tecnologia
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SFRH/BPD/70031/2010