Molecular characterization of copaiba balsam as used in painting techniques and restoration procedures

An overview of the use of copaiba balsams in paint media and in restoration practice is given. Twenty-eight samples of copaiba balsam, which were obtained from pharmacies, artists' materials suppliers, various museums and archives, were analysed by gas chromatography mass spectrometry (GCMS) in order to identify their sesquiterpene and diterpenoid constituents. Two types of copaiba balsam could be distinguished, which probably originate from Copaifera langsdorfii L. and Copaifera multijuga Hayne. In particular, the 'historical' samples, which were taken from old remnants of copaiba balsam provided by museums and archives, were produced by C. langsdorfii L., whereas the samples which are still commercially available probably originate from C. multijuga Hayne. The analyses of the 28 samples of copaiba balsam indicated that almost all of them had been adulterated with a Pinus balsam. Copaiba balsam is not stable and changes by evaporation, oxidation and polymerization. Natural aging tests showed the complete evaporation of the sesquiterpenes and the oxidation of some diterpenoid acids but also revealed various stable diterpenoid acids, which were used as marker molecules for the presence of copaiba balsam. This is illustrated by the analytical results of the samples from three paintings. 'The Girl with the Pearl Earring' by J. Vermeer (Mauritshuis, The Hague), 'Unknown Lady with a Carnation' by F. Bol (Staatlichen Museen, Kassel) and 'Farming Village at Twilight' by V. van Gogh (Rijksmuseum, Amsterdam).