Use of mid-infrared fiber-optic reflectance spectroscopy (FORS) to evaluate efficacy of nanostructured systems in wall painting conservation

Abstract

Mid-infrared fiber-optic reflectance spectroscopy (Mid-IR FORS), a sensitive, non-invasive technique for determining chemicals present on a surface, has been used to test efficacy of oil-in-water microemulsions and micellar solutions in cleaning of painted surfaces. The target of the application of these innovative nanostructured systems was the selective removal of an undesired polymeric layer from a fresco surface. The experiments were carried out by first coating frosted glass slides and painted mortar simulating a real fresco with four acrylic and vinyl polymer varnishes commonly used in wall painting restoration. Spectra of the samples were then collected by means of microreflectance single-beam infrared spectroscopy and Mid-IR FORS before and after the application of the aqueous dispersed systems based cleaning agents. Sharp, strong peaks due to the stretching of the estereous C=O bond of the polymers in a wavelength range between 1730 and 1750 cm^-1 were used as marker for the presence of these organic materials. Through Mid-IR FORS semiquantitative spectroscopy, the efficiency of the treatment has been clearly demonstrated, indicating that the nanotechnology approach represents a new, safe, and very efficient way of removing aged polymers from fresco surfaces.