Carbonation of <italic>fresco</italic> mural paintings with a dolomitic mortar: Fid-Bau Portal

Carbonation of fresco mural paintings with a dolomitic mortar

Oriols, Núria / Salvadó, Nati / Pradell, Trinitat / Jiménez, Núria / Cotte, Marine / Gonzalez, Victor / Butí, Salvador

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.

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Highlights • Short and long term carbonation process in dolomitic mortars • Influence of Mg²⁺ 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