Solvent extraction of organic compounds from oleo-resinous "megilp" paint media

'Megilp' was a gelled medium widely recommended and used during the late 18th and 19th centuries. It is a mixture of lead-treated drying oil and mastic varnish and was used by artists for both impasto and glazing. These media are associated with a tendency to darken and with particular vulnerability to solvents during cleaning. Megilp samples, naturally aged, light exposed, and thermally aged, were immersed for 24 hours in each of the series of solvents: iso-octane, xylene, dichloromethane, acetone, ethanol and water. The substances extracted from the megilps were analysed by direct temperature-resolved mass spectrometry (DTMS) and gas chromatography/mass spectrometry (GCMS). Their high sensitivity to the various solvents has been demonstrated. The extracted materials consisted mainly of fatty acids, diacids, oxidised triterpenoid compounds, triterpenoids, diglycerides, lead, polymerised resin-oil networks. The chemical constituents and their distribution in the leached megilp samples varied according to the solvents used, the relative proportions of oil and mastic in megilp mixtures, the manner of ageing and the lead compound included as drier.