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.

This work presents the results of the study of plasterwork decorations located on the stalactite vaults of the Hall of the Kings in the Alhambra (Granada, Spain) by means of Raman micro‐spectroscopy. Field investigations were carried out in situ using a portable Raman spectrometer during a conservation campaign in a completely non‐invasive manner. In addition, taking into account the results obtained, a well‐directed sampling was carried out to obtain complementary information by means of laboratory studies. Despite several practical problems during the non‐invasive field studies (like difficulties for probe positioning and vibrations of the scaffolding), almost all the pigments present in the decorations of the Hall were identified using excitation at 785 nm: cinnabar, minium, carbon black, natural lapis lazuli and synthetic ultramarine blue. In addition, evidence of different degradation mechanisms of the red pigments was obtained in situ. On the contrary, the identification of blue‐greenish and green pigments had to be performed on microsamples using a Raman microscope with excitation at 514 nm in the laboratory. In samples with blue and green areas, azurite severely degraded to clinoatacamite was identified. These were probably the remains of the oldest blue decorations. In addition, a technique for green decorations consisting on copper chlorides mixed with a small amount of lapis lazuli was identified. Other degradation products, identified in the laboratory regardless of the color of the pigment, were calcium oxalates. Finally, the laboratory studies also enabled the investigation of the stratigraphy of the pictorial layers. In this way, the presence of re‐decorations with overlaying layers of pigments even of different colors was revealed. Copyright © 2014 John Wiley & Sons, Ltd.

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A complete study of the decayed gilded decorations of the stalactite vaults in the Hall of the Kings in the Alhambra complex (Granada, Spain) has been carried out for the first time. Preliminary investigations were carried out in situ using a portable Raman spectrometer and enabled the identification of tin (II) oxide in the black areas nearby the golden flakes. This suggested the presence of an altered tin foil. Then, a comprehensive characterization of these decorations was achieved through the use of complementary nondestructive techniques working on microsamples. Two main metallic structures were identified by means of scanning electron microscopy coupled to energy dispersive X‐ray spectroscopy: (1) a thin (1–2 µm) gold leaf (probably original), and (2) redecorations with a laminated structure formed by a gold leaf placed over a thicker (10–15 µm) tin foil. Synchrotron Fourier‐transform infrared microspectroscopy revealed the use of proteinaceous glue to fix the gold leaf directly on the plasterwork, whereas in the case of the laminated structures, either glue or a natural resin was found. Raman microspectroscopy provided insight into the main decay processes affecting the gildings: the detachment of the metals due to the alteration of the organic materials employed as adhesives (forming calcium oxalates) and the oxidation of the tin foil. In addition, two technologies of false gilding have been encountered. One was based on a tin foil tinted to look like gold by means of a varnish (composed of a drying oil and a natural resin), and the second was made up with a tin–copper alloy (bronze) that appears severely degraded to copper oxalate and tin (II) oxide, as revealed by Raman microspectroscopy. Copyright © 2014 John Wiley & Sons, Ltd.

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