Carbonation of fresco mural paintings with a dolomitic mortar. (July 2022) - Oriols, Núria
Abstract: An innovative approach involving a collection of experiments to mimic and assess the different conditions (at selected time-pH-[Mg 2+ ]-humidity) existing during the carbonation process in dolomitic mortars is proposed with a combination of micro-analytical imaging techniques, namely: optical and electron microscopy, micro-Fourier-Transform Infrared spectroscopy, Raman spectroscopy and synchrotron-based micro X-ray diffraction. The carbonation process was studied from short time scale to long time scale and from simple aqueous saturated solutions to fresco mock-up samples. These techniques allowed identifying both crystallized and amorphous components and revealing their in-depth distribution in multi-layered systems. The presence of Mg 2+ influences the microstructure and composition of dolomitic mortars, resulting in the presence of aragonite concurrent to calcite. In later stages, i.e. once Ca 2+ has transformed into carbonate, brucite can lead to the formation of magnesium carbonates and hydroxycarbonates. The results contribute explaining the lability of old dolomitic mortars observed in historical fresco paintings. Graphical abstract: Unlabelled Image Highlights: Short and long term carbonation process in dolomitic mortars Influence of Mg 2+ in the microstructure and composition of the dolomitic mortar Multi-time scale experiments complemented by a multi-technique characterization High resolution synchrotron radiation μXRD maps Impact of dolomitic mortars in fresco paintings