Ageing behaviour and pyrolytic characterisation of diterpenic resins used as art materials: colophony and Venice turpentine

Abstract

The ageing behaviour of two diterpenic resins traditionally used as artists’ materials, colophony and Venice turpentine, was investigated with different spectroscopic and chromatographic techniques. In particular, three types of ageing (natural, artificial external conditions with a xenon lamp, artificial indoor conditions with fluorescent tubes) were applied to laboratory samples to study their effects on chemical structures. Thermally-assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC/MS) was employed for careful characterisation and for identification of markers compounds on the vergin resins and in the course of ageing. The most significant changes were detected in the initial part of ageing, and the principal degradation products coming from oxidation, polymerisation and cleavage reactions identified. The high intensity of xenon lamp irradiation was found to cause, apart from oxidation and polymerisation reactions, further degradation of the chemical structure with molecular fragmentation. From the analytical point of view, the differentiation between colophony and Venice turpentine with THM-GC/MS appears to depend on differences in the lower molecular weight resin components.