Carbonation of fresco mural paintings with a dolomitic mortar
Núria Oriols, Nati Salvadó, Trinitat Pradell, Núria Jiménez, Marine Cotte, Víctor González, Salvador Butí
Abstract
An innovative approach involving a collection of experiments to mimic and assess the different conditions (at selected time-pH-[Mg2+]-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 Mg2+ influences the microstructure and composition of dolomitic mortars, resulting in the presence of aragonite concurrent to calcite. In later stages, i.e. once Ca2+ 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.