Integrated Analytical Techniques for the Characterization of Painting Materials in Two South American Polychrome Sculptures

摘要

In this study, we present work on two sculptures produced in the Jesuit Missions in Paraguay in the 18th century. A combination of analytical techniques was applied for the characterization of pigments and plasters. First, cross-sections of the samples were examined by optical microscopy and SEM-EDX. Then, application of transmitted FTIR spectroscopy for selecting samples confirmed the presence of gypsum (Ca2SO4.2H2O) used as the preparation layer. Copper resinate was identified in one of the sculptures by a combination of FTIR, SEM-EDX and gas chromatography, together with its characteristic colour as observed in the cross-sections of the samples. The red pigments were identified as vermilion, hematite and minium, together with the organic pigment madder lake identified by HPLC-DAD in one of the sculptures. All these chemical results become more significant and relevant when we considered them in light of the results obtained from research on historical documents and old treatises used in the region.