Sampling problems in the radiocarbon dating of old mortars and plasters with the “pure lime lumps” technique

Rita Vecchiattini, Giovanni Pesce, Gianluca Quarta, Lucio Calcagnile

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Several scientific papers describe the radiocarbon dating of lime mortars and plasters [Folk and Valastro, 1976; Van Strydonck et al., 1992; Hale et al., 2003; Nawrocka et al., 2005]. In many cases, these lime based mixtures are dated by using pieces of organic materials contained within the mix such as charcoal, wood or straw. However, this type of application can only provide post-quem chronological information. The results obtainable, in fact, are not connected with the hardening process of lime but with the formation process of the organic material embedded in the mixture and this can be a quite important limitation, in the archaeological interpretation of the results obtained by radiocarbon dating. Rarer and with not yet fully reproducible results are the papers dealing with the radiocarbon dating of calcium carbonate contained in the mortars as binder phase. In this case, the 14 C dating is carried out directly on the calcium carbonate precipitated during the hardening process of lime by the reaction between calcium hydroxide and atmospheric carbon dioxide. As the content of 14 C contained in the newly formed calcium carbonate reflects the 14 C concentration in the atmosphere at the time of hardening, this material can be used for the radiocarbon dating of old mortars and plasters. Although the method is quite simple in its basis principle, relevant issues come from the contamination problems of the dated samples with other carbon sources. Grains of carbonate sand or underburned pieces of the same limestone used to produce the lime, that are originally mixed with the binder cannot be, in fact, completely removed from the mixtures. These materials do not contain radioactive carbon 1 but behave as the carbonated lime during the analyses. For this reason, the radiocarbon dating of old lime-based mixtures has not yet been used intensively over the past decades. Over the past years, this problem led to the development of new techniques for the sample preparation (e.g. Sonninen and Junger, 2001) and among these techniques, the so called “pure lime lumps” represents a fast and reliable method. The technique is based on the use of lumps of pure lime, very often embedded in old lime based mixtures as material for the radiocarbon dating. Because these lumps are made of pure lime [Bugini and Toniolo, 1990] any contamination problem is avoided [Pesce and Ball, 2012]. However, despite the remarkable results already achieved with this technique [Pesce et al., 2009; Pesce et al., 2012; Pesce et al., 2013], the sample collection is still a very important issue for a successful application of the radiocarbon dating. This paper describes the main sampling problems faced during a research on the accuracy and precision of the “pure lime lumps” technique, founded by the University of Genoa 2 and carried out together by the University of Genoa and the and CEDAD in Italy and the University of Bath in the United Kingdom. Results of this research were presented at the 21 st International Radiocarbon Conference, held in Paris from 9th to 13th July 2012.
Original languageEnglish
Title of host publicationOnline Proceedings of the Conference BUILT HERITAGE 2013 Monitoring Conservation and Management
EditorsM. Boriani, R. Gabaglio
Place of Publicationonline
PublisherPolitecnico di Milano
Pages1066-1074
Number of pages9
ISBN (Electronic)9788890896101
Publication statusE-pub ahead of print - 18 Nov 2013
EventBuilt Heritage 2013: Monitoring Conservation Management - Milan
Duration: 18 Nov 2013 → …

Conference

ConferenceBuilt Heritage 2013: Monitoring Conservation Management
Period18/11/13 → …

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