Study on the effects of chemical cleaning on pinaceae resin-based varnishes from panel and canvas paintings using pyrolysis-gas chromatography/mass spectrometry

Cleaning of varnish coatings is one of the most critical steps in the restoration treatment of paintings and characterization of physical and chemical processes involved in this practical procedure has attracted interest of scientists in the field of conservation. Evaluation of chemical cleaning methods based on the application of organic solvents and detergents on Pinaceae resin-based varnishes from panel and canvas paintings has been successfully carried out using pyrolysis-gas chromatograpy/mass spectrometry (Py-GC/MS). The proposed method includes the on-line derivatization of the diterpenoid resin using hexamethyldisilazane (HMDS). Analyses performed on a series of model varnish indicate that a different dissolution effect takes place on the abietadiene and pimaradiene compounds present in the pinaceae resin depending on the chemical properties of the cleaning agent. Finally, the reported procedure has been used for assessing the cleaning trials carried out prior to the restoration of the Magdalena Tryptich (Master of Alzira, 16th century, Valencia, Spain) and the canvas painting “Inmaculada” (Alonso del Arco, 1665-1670, Málaga, Spain) and for assessing the effects of an old cleaning treatment performed on a 17th century diterpenoid resin-based varnish occurring on the canvas painting collection from the Saint Joseph Church (Taormina, Italy).