Recognition of copals in aged resin/ oil paints and varnishes
The polymer fractions of three copals and sandarac were examined with direct temperature-resolved mass spectrometry (DTMS) and pyrolysis - gas chromatography-mass spectrometry (Py-GCMS) with thermally assisted methylation using tetramethylammonium hydroxide (TMAH). They were found to consist mostly of polymers of communic acid and communol. Congo copal contained ozic acid and some enantio-biformene and ozol. A new analytical approach for the identification of polymer fractions in small and insoluble paint samples is introduced. The procedure involves a two-step Py-GCMS technique with on-line derivatisation with TMAH in the first step. In the second step, traces of polymer fractions in small complex samples are analysed. A copal/oil varnish was studied. The characteristic copal components had disappeared to a large extent in the manufacturing process and especially during ageing. However, some characteristic marker compounds could still be found.
van den Berg, K.-J, van der Horst, J, & Boon, J.J. (1999). Recognition of copals in aged resin/ oil paints and varnishes. In 12th Triennial Meeting Lyon 29 August - 3 September 1999 ; Vol. II, ICOM-CC ICOM Committee for Conservation (pp. 855–861). James.