The removal of iron from waterlogged archaeological wood: efficacy and effects on the room temperature wood properties

ABSTRACT

Present results provided new information on the practice of removing iron from waterlogged wood using chelating agents. Two series of samples were selected: small waterlogged wood samples of Quercus spp., Pinus sylvestris L. and Pinus pinaster Aiton, and a portion from the dismantled shipwreck Huguangjiao I. Iron extractions were carried out using disodium ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). Samples were characterized by environmental scanning electron microscopy coupled with dispersive energy spectrometry, micro-Raman spectroscopy, atomic absorption spectroscopy, Fourier transform infrared spectroscopy and dynamic mechanical analysis (DMA), the latter used to evaluate viscoelastic properties. The extraction efficiency of both products was good, although it depended on the wood state of preservation, being higher in more decayed material. Still, the extraction procedures induced a limited effect on the decayed wood tissue, affecting both cell wall chemical composition and physical characteristics. Moreover, a significant difference existed between the two agents. In decayed hardwoods, they had an impact on both E’ (decrease) and tanδ (increase), mostly apparent for DTPA. The difference between DTPA and EDTA was also more evident when the frequency was varied in DMA tests. In contrast, the well-preserved softwood was not affected by the considered treatments.

KEYWORDS:

• EDTA
• DTPA
• treatments
• iron extraction
• dynamic mechanical analysis
• viscoelastic properties of wood

Acknowledgements

This work is part of the PhD thesis of Elisa Pecoraro. The analysed wood samples have been taken from small portions of the material collected during several years of research on waterlogged archaeological wood carried out at CNR-IBE (formerly CNR-IVALSA). All authors are very grateful to the various conservation authorities that provided the material during these years: Soprintendenza Archeologia della Toscana, Soprintendenza Archeologia, Belle arti e Paesaggio per il Comune di Venezia e Laguna and CORILA (Consorzio Ricerche in Laguna). Hainan Museum is appreciated for supplying sample XHI-174. The authors express their sincere gratitude to Nathalie Guichard (CEISAM, Chimie Et Interdisciplinarité, Synthèse, Analyse, Modélisation, Nantes University, France) for her support with AAS, and Jean-Yves Mevellec and Nicolas Stephant (Institut des Matériaux Jean Rouxel of Nantes, France) for their help with FTIR and SEM-EDS.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 For a technical problem, the containers containing both DTPA and EDTA solutions after two months of extraction were broken during transport to the laboratory for analysis. Therefore, the related data could not be reported.

Additional information

Funding

E.P. acknowledges support from Consiglio Nazionale delle Ricerche through Short-term Mobility (STM) Fellowships, call 2015. C.P.-M., G.L. and E.G. also would like to thank the French Ministry of Culture, through the “Direction Régionale des Affaires Culturelles des pays de la Loire” (DRAC) for their financial support. Financial supporters had no involvement in the study design, collection, analysis and interpretation of data, writing of the report, and decision to submit the article for publication.