Clay and alunite-rich materials in painting grounds of prominent Italian masters – Caravaggio and Mattia Preti

Abstract

Recently, the fine arts' research is increasingly carried out by non-invasive techniques, which do not require any sampling. However, some questions cannot be answered in this way. A typical example is the provenance analysis of the natural materials used in historical paintings. Another question is how much the provenance of the material is related to the provenance of the artwork itself (because of trade with pigments, painters' migration and their artistic preferences). Often, only painter's preference and intention are mentioned, and not economic factors and regional availability of the raw material. This is also the case of clay-based preparatory layers (grounds) on Caravaggio's paintings. In order to prove a connection of the ground composition with the place of the painting's creation, the painting grounds used by two prominent Baroque Masters Caravaggio and Mattia Preti have been investigated using X-ray powder micro-diffraction and Fourier transform infrared micro-spectroscopy in combination with micro-palaentological analysis. It was found that grounds applied by the same painter, but in two closely related regions – Italy and Malta, differ. While pottery clays were used in Italy, weathered Globigerina limestones were applied in Malta in combination with alunite-hematite material. It is the first time ever that such material has been identified as a main component in painting grounds.