Monitoring of pictorial surfaces by mid-FTIR reflectance spectroscopy: Evaluation of the performance of innovative colloidal cleaning agents

This study reports the use of mid-FTIR reflectance spectroscopy to evaluate the efficiency of an innovative method to remove aged polyacrylic resins from porous carbonate surfaces. Acrylic copolymers have been extensively used in recent decades as protectives and consolidants of frescoes. However, their aging produces both yellowing and serious degradation of painted layers, necessitating their removal. The evaluation of the performance of a method aimed to remove such aged polymers is often a crucial and critical problem. The innovative technique proposed here is based on the use of mid-FTIR reflectance spectroscopy in optical fibers to check the reliability of an innovative colloidal cleaning agent, namely an oil-in-water microemulsion, constituted of a four-component system consisting of water as the continuous phase, sodium dodecyl sulfate as the surfactant, 1-pentanol as the cosurfactant, and pxylene as the dispersed phase. The efficacy of this innovative method has been tested first in the laboratory and then on the surface of a Renaissance fresco by Spinello Aretino in the Cappella Guasconi at San Francesco Cathedral (Arezzo, Italy). Through mid-FTIR reflectance spectroscopic measurements performed in situ, the efficiency of the treatment has been proved, demonstrating that the nanotechnology approach represents a new, safe, and very efficient way of removing aged polymers from fresco surfaces.