Determination of materials and techniques involved in the mural paintings of San Miguel Church, Argentina

The research conducted on the mural paintings of the dome and aisles of the San Miguel Church, Buenos Aires, Argentina, is herein described in this work. Based on the results attained from the stratigraphic analysis, the technique implemented by the architect and artist Augusto Ferrari was secco. The composition of the mortar in the majority of the samples collected was gypsum (CaSO4 · 2 H2O) and calcite (CaCO3), whereas the preparation layer was mainly characterized by the presence of gypsum and cerussite (PbCO3). In addition, the red pigments were characterized in all cases as hematite (Fe2O3) whereas orange and ochre colors were achieved by mixing chrome yellow (PbCrO4), chrome orange (PbCrO4·PbO), and gypsum and barite (BaSO4). Moreover, all the range of blue samples found in this mural paintings were characterized as lazurite (Na8 [Al6Si6O24] Sn). Finally, the gildings were composed of a superficial layer of gold of approximately 5-μm thickness, followed by a layer of hematite and chrome yellow. The latter was also employed as a yellow pigment in all of the analyzed works of art. In conclusion, it was demonstrated that the use of complementary and microdestructive spectroscopic methodologies is a very useful tool to determine not only the materiality but also the execution technique of the painting in order to assess, in an interdisciplinary approach, the future restoration and preservation strategies.