Sironić, Andreja; Matulić Bilač, Žana; Španjol-Pandelo, Barbara; Krajcar Bronić, Ines
(2021)
Dating wooden artefacts treated with resins.
In: Miloglav, Ina, (ed.) Book of Abstracts, 9th International Scientific Conference Methodology and Archaeometry, MetArh. Zagreb, Faculty of Humanities and Social Sciences of the University of Zagreb, p. 43
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Abstract
The wooden Romanesque Crucifix from Collection of Sacral Art in Poreč has been restored 1994-1999 in Conservation department of Split when the multidisciplinary research detected that original Christus triumphans has been transformed into Cristus dolorens in the early 18th century. Project Ars lignea: the Woodcarving Art Heritage of the North Adriatic from 1300 until 1600 (the University of Rijeka) involved the new possibility of radiocarbon dating of original wood (poplar). A sample was taken from the Christ's corpus. The procedure of radiocarbon dating of wood, performed at the Zagreb Radiocarbon Laboratory, usually involves the so-called A-B-A or acid-base-acid chemical preclearing. The sample was inspected by microscope in order to remove larger foreign material, washed with ultrapure water and then subsequently treated by HCl, NaOH solution and again by HCl. This procedure removes carbonates and large organic molecules present in soil: fulvic and humic acids. However, it does not remove organic varnishes or other synthetic materials that might have been applied to the artefact. Since these coatings contain organic molecules, dating may lead to erroneous dates. When the coating is obvious, or there are indications that the artefact had been treated with synthetic coatings, a series of organic solvents is used for washing the sample before A-B-A procedure. The washing starts with a non-polar solvent, followed by a solvent with higher polarity and eventually ends with the most polar solvent, i.e. water. Here we present a case of a wood sample taken from the Christus dolorens that did not seem to have been treated with coatings. However, its 14C activity and δ13C value proved it was treated with resins of fossil origin. In repeated measurements, it was proved that the procedure of solvent cleaning we use is efficient in removing the coating contaminates.
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