Gold in the Alhambra: study of materials, technologies, and decay processes on decorative gilded plasterwork

Abstract

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.

Raman and Fourier transform infrared microspectroscopies reveal medieval Hispano–Muslim wood painting techniques and provide new insights into red lead production technology

“…These bands are typically associated with natural resins formed by complex mixtures of esters and polyesters of polyhydroxy acids. These features strongly resemble those obtained by our group in gilded decorations on plasterwork in the Alhambra . In certain false gildings, we found tin foil tinted to look like gold by means of a varnish composed of oil and natural resin.…”

“…These features strongly resemble those obtained by our group in gilded decorations on plasterwork in the Alhambra. [28] In certain false gildings, we found tin foil tinted to look like gold by means of a varnish composed of oil and natural resin. Thus, we can hypothesize that some areas of the ceiling were decorated with tin-based false gildings and these could be remains of the mordant employed to fix the metal or the varnish.…”

Raman spectroscopy of minerals and mineral pigments in archaeometry

“…In the last period, 2014/2015, we can cite further relevant studies on wall paintings of two Greek Byzantine Churches from Kastoria, northern Greece (Iordanidis et al); pigments in the wall paintings at Jokhang Monastery in Lhasa, Tibet, China (Li et al); a wall painting attributed to Ambrogio Lorenzetti in the St Augustine Church in Siena, Italy (Damiani et al); the pigments in dome wall paintings by Correggio in Parma cathedral (Bersani et al); 17th century mural paintings, Dominican Convent of Nossa Senhora da Saudacao, Montemor, Portugal (Gil et al); medieval Nubia wall paintings from Saras, Old Dongola and Banganarti archaeological sites (Syta et al); wall paintings in Pompeii (Madariaga et al); wall paintings from Qasr El‐Ghuieta Temple, Kharga Oasis, Egypt (Mahmoud); the wall paintings from the Baños de Doña Maria de Padilla in the Alcazar of Seville (Perez‐Rodriguez et al); binder compositions in Pompeian wall paintings from Insula Occidentalis (Gelzo et al); gilded plasterwork in the Hall of the Kings in the Alhambra complex, Granada, Spain (de la Torre‐López et al); wall paintings in the San Francisco Church, Santiago, Chile (Araya et al); the wall paintings in the Churches of Panagia and Theotokos built in the settlements of Patsos and Meronas at Amari Rethymno, Crete (Cheilakou et al); wall painting fragments from Roman villas of the Sabina area, Rome (Paladini et al); the wall paintings from the Hellenistic hypogeum of Apaforte‐Licata, Agrigento, Sicily (Aquilia et al); wall paintings in the Villa of the Papyri in Herculaneum (Amadori et al); and decorative fragments from the hypocaustum in the Roman villa of El Ruedo, Almedinilla, southern Spain (Mateos et al).…”

Applications of Raman spectroscopy in art and archaeology

“…The study of the decayed gilded decorations of the stalactite vaults in the Hall of the Kings (Alhambra complex, Granada, Spain) has been carried out for the first time by de la Torre-López et al [15] First, the in situ analysis by portable Raman spectroscopy enabled the identification of tin(II) oxide in the black areas nearby the golden flakes, suggesting the presence of an altered tin foil. Then, these decorations were characterised through the use of complementary non-destructive laboratory techniques on microsamples.…”