Characterization of pigments and binders in a mural painting from the Andean church of San Andr\xe9s de Pachama (northernmost of Chile)

Eugenia P Tomasini,Marcela Sepúlveda,Gabriela Siracusano,Magdalena Pereira,Sebastián Gutiérrez,Diana M Castellanos Rodríguez,Marta S Maier,Fernando Guzman,Carlos Rúa Landa,Valeria Careaga,José Cárcamo

doi:10.1186/s40494-018-0226-x

Abstract

The Andean church of San Andrés de Pachama is located in the highland of the northernmost of Chile, near the limit with Bolivia and next to the Ruta de la Plata. This commercial route contributed in the past to the transport and commerce of various raw materials, such as silver, from the Andean mountains region to the Pacific Ocean coast and then to the European market. The walls inside the church are decorated with paintings from the end of the eighteenth century that reproduce religious motivs together with flowers, fruits, and birds. In this study, micro samples taken from one of the mural paintings have been analysed to acquire information on the artistic materials and the painting technique previous to the restoration of the paintings. Analysis by micro-Raman spectroscopy complemented with scanning electron microscopy–energy dispersive X-ray spectroscopy, attenuated total reflection infrared spectroscopy, X-ray diffraction, and high-performance liquid chromatography with diode-array detection allowed the identification of orpiment, vermilion, indigo, smalt, antlerite, hematite, carmine lake, and wood charcoal as pigments as well as gypsum as the ground layer. Lipidic and proteinaceous materials extracted from the microsamples were identified by gas chromatography coupled to mass spectrometry and indicated the use of a mixture of egg and siccative oil as binders and a secco painting technique involving animal glue as the plaster primer. Smalt and the prized cochineal lake are reported for the first time in an Andean colonial mural painting.

Highlights

The village of Pachama is located at 3423 masl in the region of Arica-Parinacota in the northernmost of Chile and is one of various colonial towns founded along the Ruta de la Plata, a commercial route used since the sixteenth century for the transport of silver ore, commodities from Castilla and other goods from the Cerro Rico of Potosí to the Pacific Ocean [1, 2]
Calcium sulfate with different levels of hydration was detected by micro-Raman spectroscopy with characteristic bands at 418, 501, 611, 627, 676, 1017, 1111, 1130, and 1160 cm−1 (Fig. 3)
Raman spectrum of the yellow layer on the cross-section (Fig. 6) showed characteristic bands of orpiment at 293, 311, and 355 cm−1 [32, 33] together with bands at 1008 and 1017 cm−1 ascribed to Orange The orange paint in PCH03 was composed by a mixture of orpiment and hematite, in accordance with the elemental composition determined by scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS) (Fe, S, As) (Table 2) and micro-Raman spectroscopy

Summary

Introduction

The village of Pachama is located at 3423 masl in the region of Arica-Parinacota in the northernmost of Chile and is one of various colonial towns founded along the Ruta de la Plata, a commercial route used since the sixteenth century for the transport of silver ore, commodities from Castilla and other goods from the Cerro Rico of Potosí to the Pacific Ocean [1, 2]. Pigments Blue Two samples (PCH02 and PCH09) of different hues of blue (Table 1) were collected from the wall painting and analyzed by SEM–EDS and micro-Raman spectroscopy.

Results

Conclusion