Microporous electrospun nonwovens combined with green solvents for the selective peel-off of thin coatings from painting surfaces.

Over the last few decades, significant research efforts have been devoted to developing new cleaning systems aimed at preserving cultural heritage. One of the main objectives is to selectively remove aged or undesirable coatings from painted surfaces while preventing the cleaning solvent from permeating and engaging with the pictorial layers. In this work, we propose the use of electrospun polyamide 6,6 nonwovens in conjunction with a green solvent (dimethyl carbonate). By adjusting the electrospinning parameters, we produced three distinct nonwovens with varying average fiber diameters, ranging from 0.4 µm to 2 µm. These samples were characterized and tested for their efficacy in removing dammar varnish from painted surfaces. In particular, the cleaning process was monitored using macroscale PL (photoluminescence) imaging in real-time, while post-application examination of the mats was performed through scanning electron microscopy. The solvent evaporation rate from the different nonwovens was evaluated using gravimetric analysis and Proton Transfer Reaction- Time-of-Flight. It was observed that the application of the nonwovens with small or intermediate pore sizes for the removal of the terpenic varnish resulted in the swollen resin being absorbed into the mats, showcasing a peel-off effect. Thus, this protocol eliminates the need for further potentially detrimental removal procedures involving cotton swabs. The experimental data suggests that the peel-off effect relates to the microporosity of the mats, which enhances the capillary rise of the swollen varnish. Furthermore, the application of these systems to historical paintings underwent preliminary validation using a real painting from the 20th century.

Non-resonant inelastic X-ray scattering for discrimination of pigments.

Inelastic X-ray scattering (IXS) spectroscopy has been used in many fields of solid-state physics and theoretical chemistry as an accurate and quantitative probe of elementary excitations. We show that non-resonant IXS spectra in the energy loss range below 100 eV exhibit a strong contrast across a wide range of commercially available pigments, opening new routes for their discrimination. These signatures combine plasmonic transitions, collective excitations and low energy absorption edges. We have performed IXS to discriminate different artists' pigments within complex mixtures and to quantitatively determine rutile and anatase polymorphs of TiO2. The integration of experimental data on pigment powders with suitable ab initio simulations shows a precise fit of the spectroscopic data both in the position of the resonances and in their relative intensity.