Micromorphological and chemical elucidation of the degradation mechanisms of birch bark archaeological artefacts

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• 作者：Sibilla Orsini ; Erika Ribechini ; Francesca Modugno ; Johanna Klügl…
• 关键词：Archaeological birch bark ; Suberin ; Triterpenes ; SEM ; GC/MS ; Oxidation ; Depolymerisation
• 刊名：Heritage Science
• 出版年：2015
• 出版时间：December 2015
• 年：2015
• 卷：3
• 期：1
• 全文大小：3,419 KB
• 参考文献：1. Ribechini, E., Direct Mass Spectrometric Techniques: Versatile Tools to Characterise Resinous Materials, in Organic Mass Spectrometry in Art and Archaeology, M.P. Colombini and F. Modugno, Editors. 2009, John Wiley&Sons Ltd. Chichester (UK). p. 75-5.
  2. Modugno, F. and E. Ribechini, GC/MS in the Characterisation of Resinous Materials, in Organic Mass Spectrometry in Art and Archaeology, M.P. Colombini and F. Modugno, Editors. 2009, John Wiley&Sons, Ltd. Chichester (UK). p. 215-35.
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• 刊物主题：Materials Science, general;
• 出版者：BioMed Central
• ISSN：2050-7445

文摘

Introduction Since ancient times, the unique properties of birch barks (Betula genus) have made them a material of choice for producing both everyday-life and artistic objects. Yet archaeological birch bark artefacts are rare, and little is known about the chemical transformations undergone by bark (chemically composed mainly of suberin and triterpenes) in archaeological contexts. Understanding the chemical modifications induced by ageing is essential for selecting suitable preservation and conservation approaches. Thus, the main aim of this research is to assess the preservation and state of degradation of archaeological findings made of birch bark: a Neolithic bow case recovered from a melting ice patch in the Bernese Alps (Switzerland) and a waterlogged birch bark vessel discovered at Moossee Lake (Canton of Bern, Switzerland). Scanning electron microscopy (SEM) and gas chromatography/mass spectrometry (GC/MS) were used to obtain information at micro-morphological and molecular levels on the state of degradation of the birch bark findings. GC/MS analysis followed two different sample preparations, alkaline hydrolysis and solvent extraction, in order to investigate respectively the hydrolysable and soluble constituents, and to test whether part of the suberin structure was depolymerised by the long period of burial. Results and conclusions SEM investigations on archaeological birch bark samples have shown that the extent of degradation of the microstructure is much higher in waterlogged birch bark than in birch bark preserved in ice. GC/MS analysis revealed that at a molecular level, the birch bark was quite well preserved. In both the archaeological environments, ice patch and lake water, various reactions had taken place leading to the depletion of reactive and sensitive compounds such as unsaturated acids and epoxy-compounds. In addition, archaeological birch bark had undergone depolymerization and oxidation reactions leading to the appearance of free suberin monomers and of oxidised triterpenes (betulone and lupenone). GC/MS data also seems to suggest that the birch bark preserved in the waterlogged site had a more pronounced degradation both in terms of oxidation and depolymerisation.