Characterization of Wall Paintings of the Harem Court in the Alhambra Monumental Ensemble: Advantages and Limitations of In Situ Analysis

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.

New Insights into the Medieval Hispano-Muslim Panel Painting: The Alfarje Found in a Balearic Casal (Spain)

“…Observed with polarized light, the particles exhibit pleochroism typical of azurite. In Figure 3 b accessory minerals that usually accompany azurite, such as quartz, calcite, and clayey minerals, are also seen [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. Natural cinnabar (HgS) is recognized by the characteristic intense red-orange color of its particles, which also exhibit high relief, prismatic habit, and angular shape due to the crushing process, as shown in Figure 2 a–c and Figure 3 c [ 15 , 35 ].…”

“…The study of the binding media used in the plasterworks from the hall of the king and the hall of the beads was performed by GC-MS [ 21 ]. The pigments used in the Lions Courtyard and the Hall of Ambassadors were studied through a multi-technique strategy that combines optical microscopy with SEM-EDX, Fourier transform infrared (FTIR), μFTIR, Raman and μRaman spectroscopies, and GC-MS [ 22 , 23 , 24 , 25 ]. Mudéjar monuments, such as the Casa de Pilatos palace (Seville), have been analyzed by portable X-ray fluorescence (XRF), SEM-EDX, optical microscopy, μRaman, and μFTIR [ 26 ].…”

A Skin to Live in: Geometric Parietal Paintings in the Residential Architecture of al-Andalus

“…Some of them might have been applied with the secco-technique (cf. Arjonilla et al 2022) to cover the blank spaces in geometric panels using tempera paint. This mixed technique would allow the meticulous detail required by small, complex motifs that were traced with greater detail and required more time to execute, but they are not as frequently preserved (cf.…”