New insights into molecular evolution of oil/colophony varnishes: towards pyrolysis-gas chromatography/mass spectrometry-based quantitation: Evolution of oil/colophony varnishes

Mixtures of a drying oil with a Pinaceae resin are among the most widespread natural varnish formulations encountered in coating of artifacts. GC/MS and Py-GC/MS are to date the choice analytical methods in the cultural heritage field for their qualitative molecular identification.This research was carried out on reference varnish films made with various proportions of linseed oil and colophony aged naturally in the same conditions for one year. It aimed at (1) better understanding the influence of the various proportions of oil and resin on the molecular composition of the reference films, and (2) suggesting a Py-GC/MS semi-quantitative method applicable to micro-samples. Qualitative analysis of these reference varnishes and of a historical film is first presented. Then, semi-quantitative analysis of the reference films suggested that the reaction mechanisms involved in their ageing processes are highly related to each ingredient’s proportions. Linseed oil may have an activating role in oxidation reactions occurring on colophony compounds, and the conservation state of varnishes could thus be closely linked to the resin’s proportions. Such results provide new insights into molecular evolution of linseed oil/colophony varnishes, and the semi-quantitation seems useful to further explore mechanisms occurring between diterpenoids and fatty acids.