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Aging and yellowing of triterpenoid resin varnishes - Influence of aging conditions and resin composition

Dietemann, Patrick, Higgitt, Catherine, Kalin, Moritz, Edelmann, Michael J, Knochenmuss, Richard and Zenobi, Renato (2009) Aging and yellowing of triterpenoid resin varnishes - Influence of aging conditions and resin composition. Journal of Cultural Heritage, 10 (1). pp. 30-40. ISSN 1296-2074


The aging of natural triterpenoid resins used as varnishes on paintings is still insufficiently understood. Although progress has been made, questions concerning the aging pathways in light vs. darkness, or the correlation of oxidation with yellowing, remain open. The influence of aging conditions, primarily the amount of light, but also resin composition, on the aging process were investigated. The aging reactions are followed using a variety of mass spectrometric and spectroscopic techniques. Aging processes in dammar and mastic varnishes are shown to be more dynamic and extensive than had generally been believed. In unaged bulk resins, large quantities of radicals develop within weeks after application as a varnish, due to the greatly increased surface-to-volume ratio. This is true for all aging conditions, including aging in darkness, and is accompanied by considerable oxidation as well. After a few months, most of the initial triterpenoids are oxidized. Natural aging in light and darkness leads to the same main aging products. All these findings point to the conclusion that aging largely proceeds by the same pathways in both light and darkness, mainly autoxidation. Without light, enough radicals are formed to maintain extensive autoxidation, although more slowly. Thus, differences between light and dark aging mechanisms are much smaller than often believed. In mastic, the absence of the polymeric constituents is found to enhance oxidation, but reduce yellowing. It appears that the polymer acts as a natural radical stabilizer, favoring the pronounced intrinsic yellowing tendency of mastic. The manipulation of resin composition might lead to improved aging properties of triterpenoid resin varnishes

Item Type: Article
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Additional Information: Author can archive post-print (ie final draft post-refereeing); Publisher's version/PDF cannot be used
Keywords: Natural resins; Triterpenoid resins; Varnish; Aging; Mass spectrometry of resins; Electron paramagnetic resonance spectroscopy of resins
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Date Deposited: 22 Feb 2010 11:49
Last Modified: 22 Feb 2010 11:49


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