ABSTRACT
Non-invasive techniques (X-ray fluorescence, XRF, and Raman spectroscopy) were used for the study of the Hispano Muslim wall paintings. Principal component analysis (PCA) was performed on the semi-quantitative XRF results directly provided by the in-built factory calibrations with minimum user manipulation. The results obtained were satisfactory and highlighted differences and similarities among the measurement points. In this way, it was possible to differentiate the decorations carried out on gypsum plasterwork and the wall paintings over lime plaster. The color palette, revealed by combining the results from XRF and Raman spectroscopies, comprised the pigments hematite, lapis lazuli, cinnabar (in poor conservation state), and possibly, carbon. Evidence of past interventions was also provided by PCA on XRF data, which detected the presence of Pb, Ba, and Zn in some areas. Furthermore, the preparation layers have been studied in detail on cross-sections of two microsamples. Several layers of lime plaster with a compact microstructure have been observed. The characteristic of the pictorial layer and the identification of calcium oxalate point to the use of a secco-technique. The main alteration identified was a gypsum surface layer covering the painting and signs of plaster deterioration due to gypsum migration to more internal areas. Finally, the comparison with the observations made by restorers in previous interventions on these paintings revealed the importance of the representativeness gained with the in situ study, which enabled the analysis of a high number of areas.
ABSTRACT
A totally non-invasive in situ investigation in one of the main halls of the Palace of the Lions in the Alhambra (Granada, Spain) has been carried out. Analyses were made with a fiber-optic portable Raman microspectrometer placed on scaffolding platforms at a height of ca. 12 m above the ground level during the period of conservation works. The objects of this study are the decorated plasterworks in the seven vaults of the Hall of the Kings. Together with the results, the different practical problems related to the positioning of the instrumental setup and the influence of the local environment during the analysis are discussed. In general, high quality spectra were obtained despite difficulties for micro-probe head positioning and sometimes the vibrations of the corresponding scaffold. Different typical antiquity pigments have been identified: cinnabar, minium, carbon black and lapis lazuli. Furthermore, the luminescence pattern from lapis lazuli found in most blue decorations has allowed the establishment of the natural origin and provenance of the pigment. Apart from this natural lapis lazuli, synthetic ultramarine blue was also found in one of the vaults showing up a recent restoration. In addition, some degradation products of cinnabar and minium were identified, with the major advantage of providing real-time information to the conservators during their work.
