GC-MS characterization of proteinaceous and lipid binders in UV-aged polychrome artifacts

This paper presents an analytical procedure based on gas chromatography separation and mass spectrometric identification, which allows the determination of natural resins, waxes and lipids in the same microsample (< 1 mg). By this way, the chemical characterization of dammar and mastic resins, used on their own and also in mixture with wax and oils in paint varnishes, is achieved. The triterpenoid composition of raw commercial resins was compared with that of samples collected from reference varnish layers prepared at Opificio delle Pietre Dure (Florence, Italy): a profound change in the varnish chemical composition was found after only 6 months exposure to daylight. The identified terpenoid compounds which resulted more stable to oxidation and polymerization are pentacyclic triterpenoids, such as <alpha>- and beta -amyrone and 28-norolean-17-en-3-one. The presence of these compounds in varnish samples from the Madonna col Bambino by Coppo da Marcovaldo tend of 13th century), currently being restored at Opificio delle Pietre Dure (Florence, Italy), enabled us to identify dammar and mastic resins.