A multi-analytical investigation of the materials and painting technique of a wall painting from the church of Copacabana de Andamarca (Bolivia)

The Andean church of Our Lady of Copacabana de Andamarca in Bolivia was built in 1723. Its walls are made of adobe bricks and are decorated with paintings dated from mid 18th century. Before a restoration process involving the governments of Bolivia and the Federal Republic of Germany, seven microsamples were extracted from representative colors of one of the wall paintings inside the church. The aim of our research was to characterize the chromatic palette and investigate the painting technique of this Andean colonial wall painting. To approach these goals, an integrated investigation comprising Raman and FTIR-ATR spectroscopy, optical microscopy (OM), scanning electron microscopy with X-ray microanalysis (SEM-EDS), gas chromatography (GC), and gas chromatography mass spectrometry (GC-MS) was carried out. The results indicated the use of a mixture of two basic copper sulfates of mineral origin, brochantite and antlerite, as the green pigment, adding relevant information to the palette of green pigments in colonial art. Yellow, orange and red ochre, abundant pigments in the Andean region, were also characterized. Observation by optical microscopy of cross-sections of the embedded microsamples and analysis of organic binders by GC and GC-MS pointed to a secco technique and the use of a mixture of egg and vegetable oil (tempera grassa) as the pigment binder. In conclusion, our results allowed to establish the pigment palette and offered new insights into the painting technique of Andean wall paintings. (C) 2016 Elsevier B.V. All rights reserved.