Identification and characterization of basic copper sulfates as mineral green pigments in Andean colonial mural paintings: Use of temperature‐controlled stage for the study of thermal induced antlerite degradation

Abstract

This work describes the characterization of green pigments in wall paintings from the Andean churches of San José de Soracachi and Santiago de Callapa in Bolivia, located on an ancient colonial commercial route known as the Silver Route. To approach our goal, microsamples extracted from the mural paintings and mineral samples, from a mine of the same area, were studied by using micro-Raman spectroscopy complemented with micro-energy-dispersive X-ray fluorescence spectroscopy (μ-EDXRF) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) analysis. The use of gypsum as the preparation layer was detected, and it suggests a secco painting technique. Antlerite, a basic copper sulfate, was identified suggesting a preference for its use as green pigment in the mural paintings of Andean churches that may be related to the local availability of this mineral. Indeed, this study revealed the presence of heterogeneous particles of the basic copper sulfate together with aluminosilicates, quartz and iron oxides among others, which points to a mineral origin of the green pigment because the same compounds were found in the samples taken in the mine. Because a phase transition has been noticed during the Raman analyses, due to a high power of the laser radiation, some tests have been carried out, varying the laser power, and coupling the Raman spectrometer to a temperature-controlled stage to verify under which conditions the degradation of the mineral sample of antlerite occurs

Methodologies for the Characterization and Identification of Natural Atacamite as a Pigment in Andean Colonial Painting

“…The main bands identifying this mineral are 148 and 119 cm −1 , corresponding to O-Cu-O bending; 262 cm −1 to lattice modes; 362 cm −1 to Cu-Cl stretching; 513 cm −1 to CuO stretching; and 819, 911, and 973 cm −1 to O-H deformation [19,20]. Additionally, one of the samples (ANC05 (AN) in Figure 3) shows bands at 144, 262, 411, 481, 597 986, 1070, and 1168 cm −1 , corresponding to another copper compound, antlerite (Cu3SO4(OH)4) [21], which has already been identified in Andean mural paintings [3,4,22] and has recently been found together with atacamite [23].…”

“…Heritage 2023, 6, FOR PEER REVIEW 2 During our investigations on the materials used in Andean Colonial art, some objects studied were shown not only to contain materials of European origin but also materials that were already known in pre-Hispanic times. Although European painting manuals circulated in America, our research work in the last decade has demonstrated the use of local minerals such as atacamite, cerussite, brochantite, antlerite, and lapis lazuli as pigments [1][2][3][4]. Atacamite, a basic copper chloride (Cu2Cl(OH)3), was identified and characterized for the first time in Spanish American Colonial art in a gilded and polychrome sculpture manufactured from maguey wood of Our Lady of Copacabana (1583) within the Viceroyalty of Peru [5,6], by applying Raman microspectroscopy and SEM-EDX as complementary techniques [1].…”

Tribute to Derek Long: An instant snapshot of the development of Raman spectroscopy and its application in the fields of instrumentation and methodology, solid‐state materials, cultural heritage, DFT modeling and applications in biology, microbiology, and medicine

“…Tomasini et al ( Identification and characterization of basic copper sulfates as mineral green pigments in Andean colonial mural paintings. Use of Temperature‐controlled stage for the study of thermal induced antlerite degradation , CONICET, Brazil) [ 27 ] describe the characterization of green pigments in wall paintings from the Andean churches in Bolivia, located on the ancient Silver Route. Microsamples extracted from the mural paintings and mineral samples were studied by using micro‐Raman spectroscopy complemented with micro‐energy‐dispersive X‐ray fluorescence spectroscopy (μ‐EDXRF) and scanning electron microscopy with energy‐dispersive X‐ray spectroscopy (SEM‐EDS) analysis.…”