Poly(vinyl alcohol)-borax films as cleaning agents for icons

Abstract

The efficacy of poly(vinyl alcohol) and borax (PVA-b) films to remove varnishes of natural resins from paint samples is studied. Samples prepared according to the egg tempera technique were varnished with mastic, dammar (triterpenoid resins), sandarac, copal, colophony (diterpenoid resins), and shellac and were subjected to artificially accelerated UV-aging conditions. The efficacy of the PVA-b films to remove the aged varnishes, thus cleaning the sample surfaces without using any organic solvent, is evaluated using optical microscopy in visible and UV light, optical coherence tomography, Fourier transform infrared spectroscopy, and Raman spectroscopy. The characterization of the PVA-b films is extended to rheological measurements, whereas water contact angle and pH measurements provide evidence about the formation of polar, hydrophilic groups during aging. Concerns related to potential side effects of the suggested cleaning method are addressed such as the effect of the PVA-b film on the egg tempera paint layer and the possible film residue left on a sample surface after the removal of the PVA-b film. It is reported that the method provides very good results in the removal of the triterpenoid resins and shellac, whereas the removal of the diterpenoid resins is accompanied by noticeable side effects. The suggested cleaning method was applied to remove old shellac varnishes from two icons which date to the nineteenth c. Τhe varnish in one of the two icons was in a very poor condition consisted of a very dark layer of shellac and dirt with intense craquelure. In this case, the cleaning process was modified and reinforced by heating the PVA-b film in situ.