Romantic restorations in the Alhambra monument: Spectroscopic characterization of decorative plasterwork in the Royal Baths of Comares

The polychrome plasterwork decorations of the Room of the Beds in the Royal Bath of Comares of the Alhambra monumental ensemble have been studied using Raman microspectroscopy and complementary techniques. This area keeps the testimony of the controversial restorations carried out in the 19th century in an attempt to imitate the lost original appearance of the authentic Nasrid plasterwork. Raman spectroscopy and energy dispersive X-ray fluorescence have been employed to identify the pigments and extenders. Scanning electron microscopy-energy dispersive X-ray spectroscopy has been used to gain additional information about the morphology of the painting layers. Additionally, infrared microspectroscopy provided insight into the nature of the organic materials employed as binders. Vermillion, synthetic ultramarine blue, hematite, and carbon black were clearly identified in red, blue, brown, and black decorations by Raman spectroscopy. Green decorations were executed with a copper-arsenic pigment that could not be unambiguously identified although the presence of Raman bands typical of arsenate stretching bands could point to alteration processes of copper arsenite pigments. Regarding the execution technique, the pictorial layer was applied over a preparation layer of white lead that also contained barite using a proteinaceous binder. The presence of anglesite and other phases related to hydrocerussite alteration due to humidity and salts was also evidenced. Finally, a comparison of the materials found in this redecoration with those identified in original Nasrid decorations has been performed, revealing noticeable differences in both the materials and the execution technologies.