Mass spectrometry of resinous compounds from paintings: characterisation of dammar and naturally aged dammar varnish by DTMS and HPLC/GC-MS

Several mass spectromeric techniques direct temperature mass spectrometry (DTMS), gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) in combination with GC-MS were applied in order to obtain information at the molecular level about the ageing processes occurring in dammar resin used as a varnish on easel paintings. Fresh dammar, aged dammar varnish from Rembrandt's 'Jewish Bride', and naturally aged dammar varnish obtained from several paintings were compared. A new reversed phase HPLC method was developed for separation of fresh dammar and aged dammar varnishes. Rapid fingerprinting of the fresh and aged dammar was achieved with DTMS using low voltage electron impact ionisation (EI) and ammonia chemical ionisation (CI) techniques. Structural changes due to ageing could be identified as side chain modifications of the dammarane skeleton. Artificially light-aged dammar shows a different DTMS spectrum which suggests a difference in degradation mechanism compared to milder conditions on paintings.