Materials and techniques used in high-baroque stucco decorations by Baldassarre Fontana in Kroměříž Chateau, Czech Republic

This study investigates the materials and construction techniques employed in the Baroque stucco decorations of the Ground Halls at Kroměříž Château, executed by one of the most renowned stucco-makers of the time, Baldassare Fontana and his workshop. Sixteen samples were analysed using a combination of optical microscopy, SEM-EDS, XRD, thermal analysis, and acid dissolution technique to characterize binders, aggregates, and layer compositions. The results revealed a deliberate selection of high-purity calcitic lime, sourced from Devonian limestone near Přerov, and gypsum likely from the Ketř-Opava basin, both of which were processed with minimal impurities. Two distinct mortar types were identified: a lime-gypsum-sand core modelling mortar and a lime-rich fine finishing stucco mortar. The analysis highlighted layered construction techniques. The presence of crushed marble in some specific decorations suggests a change of the recipe and indicates that the decoration of the halls was not carried out in one single phase, and perhaps some parts were not executed under Fontana’s auspice. The analytical results also point out the technological features linked to the adaptations to local material conditions. Surface coatings were initially limited to white limewash, with later interventions introducing coloured paint layers, identifiable by zinc white pigments. The findings shed light on the material practices of 17th-century stuccatori and offer a foundation for further conservation and historical research.