Artificial ageing of varnish triterpenoids in solution

A new photochemical method is presented for the artificial ageing of the tr iterpenoid resins dammar and mastic, which are commonly used as painting va rnishes. Varnish samples in solution are exposed to the radiation of a fluo rescent tube device. The solvents dichloromethane (DCM) and acetone, and th e photosensitisers Merocyanine 540 (MC540) and FotoFenton 2 (FF2) dissolved in acetonitrile (ACN) or DCM were found to generate reactive species, whic h induce similar oxidation and cross-linking processes in the triterpenoid samples as found in varnish films on paintings. This method provided inform ation on the oxidation mechanisms of the model compounds hydroxydammarenone (3) and oleanolic acid (8). Furthermore, evidence was found that the forma tion of high molecular weight material is important for the yellowing behav iour of triterpenoid varnishes. This method of solvent ageing can be succes sfully used for the preparation of cross-linked fractions of aged dammar an d mastic varnishes. (C) 2000 Elsevier Science S.A. All rights reserved.