Commercial Ca(OH)2 nanoparticles for the consolidation of immovable works of art

Calcium hydroxide nanoparticles are effective components for the consolidation treatment of immovable works of art, such as carbonate stone and wall paintings that exhibit both surface and structural degradation. Several formulations have been recently developed, with different characteristics (dispersing solvent, particle size distribution and particle structure), which are expected to result in different long-term consolidating properties. In this contribution, the carbonation of a commercial Ca(OH)2 nanoparticle formulation (Nanorestore®) was characterized through Fourier transform infrared (FTIR) analysis. Nanoparticle films were laid on KBr pellets and stored at room temperature under controlled relative humidity and CO2 pressure. FTIR analysis was used to quantitatively detect the formation of calcium carbonate. Fitting of the experimental data allowed the description of the mechanism of carbonate nucleation and growth. The compatibility of the Nanorestore® formulation for wall painting consolidation was assessed through optical and electron microscopy, colorimetry and water absorption capillarity measurements. The formulation's effectiveness in consolidating powdering painted layers was assessed through application on site and on detached samples of Mesoamerican wall paintings belonging to the pre-Columbian archaeological sites of Ixcaquixtla and Calakmul (Mexico).