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Non-destructive techniques for in situ studies of easel paintings: development and application of a X-ray micro-fluorescence confocal system

Otros títulosTécnicas no destructivas para el estudio in situ de pinturas de caballete: desarrollo y aplicación de un sistema de micro-fluorescencia de rayos X confocal
AutorLaclavetine, K.
DirectorRespaldiza, M. A. ; Ager, F. J.
Fecha de publicación2015
EditorUniversidad de Sevilla
ResumenThis PhD thesis entitled “Non-destructive techniques for in situ studies of easel paintings: development and application of a confocal X-ray micro-fluorescence system.” with the supervision of Prof. Miguel Ángel Respaldiza and Dr. Francisco J. Ager was focused on physics applied to Cultural Heritage. The main goal of this research was to design and characterize the capabilities of a portable confocal μXRF system that allows the noninvasive in situ analysis of easel paintings in combination with other spectroscopic and multispectral techniques, more specifically, XRF, IRR and UV-induced visible fluorescence. The potential of this device was proved in a particular problem in the fields of Cultural Heritage and Art History: the characterization of the techniques and the palette of the 16th century Spanish painter Alonso Vázquez and the confirmation of the authorship of some unsigned paintings, on the basis of material study. For this purpose, a methodology involving those techniques was proposed. The first part of this PhD thesis was dedicated to the design, development and in situ application of several setups (PIRR, X-Panda and μXRF-CONCHA devices). A big effort was made to design in situ working setups allowing the study of artworks directly in the places of exhibition. It provides access to unique items that cannot leave their storage or exposition room. This work concerned not only the methodological application of the techniques and characterization of the setups but also the mechanical engineering and computing developments. Several routines based on LabVIEW platform were developed in order to control the portable devices. A particular interest was focused on the treatment of the obtained data. A specific methodology was applied in order to achieve the analysis of XRF spectra obtained by CXRF using PyMCA software. Moreover, particular attention was paid to the production of mosaics of up to hundreds of IRR images comparing three software packages (VARIM, Autopano Giga and Microsoft ICE). In fact, obtaining a unique image of the entire artwork showed to be crucial in order to enhance the strategy applied in the analysis by other techniques such as XRF and CXRF. The constructed μXRF-CONCHA device is the first of its kind in Spain and one of a few available around the world. It is also probably the first CXRF setup with the ability to perform in situ analysis. Before to start the analysis of artworks, a series of experimental paint multilayers made like old paintings were studied with IRR and CXRF setups. The second part of the research consisted in developing specific methodologies in order to analyze more complex paintings. On one hand, a comparison study of the performance of three IRR technologies (Si-CCD, InGaAs and Vidicon tube) was done. The Si-CCD camera have to be used together with a UV-visible light cut-filter in order to provide results comparable to those obtained with InGaAs and Vidicon cameras. The results obtained proved that the three IRR technologies allowed the observation of preparatory drawings made in carbon black. This study also achieved the classification of the IR reflectivity of several inorganic pigments. The results showed that it is possible to discriminate different inorganic pigments with the same color observing IRR images. They confirmed the possibility of a first interpretation about the pigments presents based on IRR images. On other hand, the experimental samples were studied with the μXRF-CONCHA device. The results were successfully compared with two other CXRF systems, the LouX3D at the C2RMF in Paris and the CXRF set-up at AGH University of Science and Technology in Krakow. This
intercomparison study confronted the composition and sequence information obtained. The results achieved with the three devices are similar in spite of some technical differences. The in-depth measurements showed that the μXRF-CONCHA set-up allows to carry out the compositional analysis with depth resolution in a nondestructive way. In most of the cases, it was possible to characterize the composition and sequence information of the multilayered samples. However, sometimes the data interpretation revealed to be quite complex. Absorption effect is the principal limitation of this technique. The problem when considering 16th century paintings is the use of pigments composed of heavy elements (e.g. Pb or Hg) which masked the signals from the ground layer or the priming layer. As the last part of this PhD, seven paintings attributed to Alonso Vázquez were studied. This artist left paintings on both sides of the Atlantic, although unfortunately, several examples preserved, particularly in Mexico, are decontextualized and remain unsigned. As Alonso Vázquez was among the first Spanish painters to work in New Spain, the study of his Mexican artworks is important to Art History in order to assess his real influence on the evolution of the art in Mexico. In order to compare the paintings, this study took as reference the artworks with confirmed authenticity defining the techniques and palette of this artist. The IRR study revealed very few preparatory drawings carried out by carbon black. All these drawings were used in geometric elements difficult to produce without drawing them first. The paint application revealed to be sharp, the border of the bodies and clothes were corrected using the same mixture of dark pigments used in the decorated adjacent parts. More pentimenti are observed on decorative items such as dishes, cutlery, pots, etc. The complementary results obtained with UV and IRR were used in order to select the area study of XRF and CXRF. A novel methodology was proposed and validated in the XRF data interpretation in order to normalize the results and be able to compare them. The XRF results allowed a synthesis of the pigments detected on each artwork (lead white, vermilion, tin-lead yellow, massicot, ochres, azurite, green Cu-based pigment, umber). The different tones were obtained by applying the same mixtures with some variations from one painting to another. Comparing the five artworks from Seville, the palette of inorganic pigments used is very similar. This study confirmed the attribution of both the “Inmaculada”
and the “Sagrada Cena”. Based on the Sevillan study, the results obtained from the two Mexican paintings showed that the palette detected on the “Martirio de San Hipólito” is consistent with the artworks from Seville while the palette on the “Virgen de las Uvas” differs drastically. In the case of the “Virgen de las Uvas”, the blue and green colors cannot be explained by the use of inorganic Cu-based pigments as observed on the artworks from Seville. The results excluded “Virgen de las Uvas” and confirmed the attribution of the “Martirio de San Hipolito” as the first Mexican painting attributed to Alonso Vazquez by both archaeometric and art historical studies. Moreover the integrity of the composition showed by IRR and XRF suggested that the representation of Hernán Cortés is contemporary to the “Martirio de San Hipolito”. Consequently the portrait of the Spanish conqueror may be the oldest known. In-depth profiles were focused on painting areas free of heavy elements. The presence of ground and priming layers revealed by in-depth CXRF scans were compared to SEM-EDS study. The ground layers were made of Ca. In the case of the priming layer, both techniques revealed the use of red ochre priming with exception of the “Sagrada Cena” which in-depth scans showed the presence of a second Pb-based priming layer. The use of two kinds of priming in a same artwork may be present in other artworks of Alonso Vazquez and could be studied in future. CXRF demonstrated its sefulness when the interpretation of XRF results is not trivial due to the presence of several pigment layers. Finally, CXRF was proven to be a very promising technique for performing depth-resolved chemical analyses. Although some limitations could appear when heavy element based pigments are present. In the study of old paintings, it can provide complementary results to the classical extraction of stratigraphic micro-samples providing an alternative noninvasive analysis. CXRF combined with IRR and XRF gives to the archaeometric study the ability to define the inorganic pigments palette and techniques used by painters.
DescripciónTesis doctoral presentada por Kilian Laclavetine. Programa de doctorado de Física Nuclear, en el Departamento de Física Atómica, Molecular y Nuclear de la Universidad de Sevilla.
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