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Testing the Effectiveness of Protocols for Removal of Common Conservation Treatments for Radiocarbon Dating

Published online by Cambridge University Press:  09 August 2017

Fiona Brock ,
Michael Dee ,
Andrew Hughes ,
Christophe Snoeck ,
Richard Staff  and
Christopher Bronk Ramsey
Fiona Brock*
Affiliation:
Cranfield Forensic Institute, Cranfield University, Defence Academy of the United Kingdom, Shrivenham, Oxon, SN6 8LA, United Kingdom
Michael Dee
Affiliation:
Research Laboratory for Archaeology & the History of Art, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, OX1 3QY, United Kingdom Centre of Isotope Research, Faculty of Science & Engineering, University of Groningen, Energy Academy Europe Building, Nijenborgh 6, 9747 AG Groningen, The Netherlands
Andrew Hughes
Affiliation:
Pitt Rivers Museum, University of Oxford, Oxford, OX1 3PP, United Kingdom
Christophe Snoeck
Affiliation:
Research Unit: Analytical, Environmental & Geo-Chemistry, Dept. of Chemistry, Vrije Universiteit Brussel, ESSC-WE-VUB, Pleinlaan 2, 1050 Brussels, Belgium
Richard Staff
Affiliation:
Research Laboratory for Archaeology & the History of Art, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, OX1 3QY, United Kingdom Scottish Universities Environmental Research Centre (SUERC), University of Glasgow, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, G57 0QF, United Kingdom
Christopher Bronk Ramsey
Affiliation:
Research Laboratory for Archaeology & the History of Art, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, OX1 3QY, United Kingdom
*
*Corresponding author. Email: f.brock@cranfield.ac.uk.
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Abstract

To achieve a reliable radiocarbon (14C) date for an object, any contamination that may be of a different age must be removed prior to dating. Samples that have been conserved with treatments such as adhesives, varnishes or consolidants can pose a particular challenge to 14C dating. At the Oxford Radiocarbon Accelerator Unit (ORAU), common examples of such substances encountered include shellac, the acrylic polymers Paraloid B-67 and B-72, and vinyl acetate-derived polymers (e.g. PVA). Here, a non-carbon-containing absorbent substrate called Chromosorb® was deliberately contaminated with a range of varieties or brands of these conservation treatments, as well as two cellulose nitrate lacquers. A selection of chemical pretreatments was tested for their efficiency at removing them. While the varieties of shellac and Paraloid tested were completely removed with some treatments (water/methanol and acetone/methanol/chloroform sequential washes, respectively), no method was found that was capable of completely removing any of the vinyl acetate-derived materials or the cellulose nitrate lacquers. While Chromosorb is not an exact analog of archaeological wood or bone, for example, this study suggests that it may be possible to remove aged shellac and Paraloid from archaeological specimens with standard organic solvent-acid-base-acid pretreatments, but it may be significantly more difficult to remove vinyl acetate-derived polymers and cellulose nitrate lacquers sufficiently to provide reliable 14C dates. The four categories of conservation treatment studied demonstrate characteristic FTIR spectra, while highlighting subtle chemical and molecular differences between different varieties of shellac, Paraloid and cellulose nitrate lacquers, and significant differences between the vinyl acetate derivatives.

Keywords

chemical analysiscontaminationradiocarbon AMS dating
Type
Research Article
Information
Radiocarbon , Volume 60 , Issue 1 , February 2018 , pp. 35 - 50
Copyright
© 2017 by the Arizona Board of Regents on behalf of the University of Arizona 

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