Portable X-ray fluorescence (pXRF) has been demonstrated as a powerful tool to assign obsidian artifacts to sources. Newer instruments can even match artifacts from some regions to their sources in a matter of just seconds, not minutes. There remains, however, a reluctance to use pXRF instruments to characterize the sources themselves. Many past studies have used pXRF in a region where the sources have been well characterized using lab-based techniques. That is, earlier analytical work established compositional types for the obsidian sources, and pXRF was later used to sort artifacts into those types. This is due, at least in part, to notions that pXRF instruments are insufficiently accurate or reliable to characterize the sources. The motivations to use pXRF for characterizing sources are similar to those for sourcing artifacts: many more specimens can be analyzed without concern for the financial, practical, and legal considerations associated with instruments in distant facilities. This paper documents tests conducted to investigate the accuracy and reproducibility of pXRF data relative to five laboratory-based techniques (NAA, EDXRF, WDXRF, EMPA, and LA-ICP-MS) with a focus on Armenian obsidian sources. These tests demonstrate that there is no reason to believe pXRF is inherently inaccurate, unreproducible, or otherwise inadequate for source characterization. A case study of the Pokr Arteni source highlights the advantages of pXRF, including the capability to analyze large numbers of specimens, recognize variability, and elucidate field relationships. In these respects, pXRF can facilitate more sophisticated obsidian sourcing studies.
Bibliographical noteFunding Information:
I am indebted to dozens of individuals whose contributions made this study possible and practical. Pavel Avetisyan, Director of the Institute for Archaeology and Ethnography, National Academy of Sciences, Armenia is thanked for his on-going support of the projects in which I am involved. My co-directors on the Obsidian Resources and Landscapes of Palaeolithic Armenia project are Boris Gasparyan, Institute of Archaeology and Ethnography and Daniel S. Adler, Old World Archaeology Program, University of Connecticut. Fellow members of the Hrazdan Gorge Palaeolithic Project (directed by Adler, Gasparyan, and Benik Yeritsyan, Institute of Archaeology and Ethnography), particularly Keith Wilkinson, Beverly Schmidt-Magee, Philip Glauberman, and Yannick Raczynski-Henk, are thanked for their contributions to our shared research aims. I collected a portion of the Armenian obsidian specimens in this study with my collaborators Khachatur Meliksetian and Sergei Karapetian, Institute of Geological Sciences, National Academy of Sciences, Armenia. My sampling and surveying at the Arteni volcanic complex was assisted by Suren Kesejyan. Additional Southwest Asian obsidian specimens related to this study were collected by George “Rip” Rapp (University of Minnesota–Duluth), Tuncay Ercan (Directorate of Mineral Research and Exploration, Turkey), John Whittaker and Kathryn Kamp (Grinnell College), Albert Harutyunyan (State Engineering University, Armenia), Ruben Badalian (Institute of Archaeology and Ethnography, Armenia), Nino Sadradze and Givi Maisuradze (Institute of Geology, Georgia), Robert L. Smith (United States Geological Survey), James F. Luhr and Ivan P. Savov (Global Volcanology Program, Smithsonian Institution), and M. James Blackman (Smithsonian Institution). NAA and EDXRF data for a portion of these specimens were provided by Michael Glascock, Archaeometry Laboratory, University of Missouri Research Reactor. Mexican obsidians also used in inter-technique calibration were provided by Magen Coleman, who also collected comparative NAA and EDXRF data as part of her Master's research at the University of Missouri. The pXRF instrument that I used for the analyses in Sections 3, 4, 5, and 7 is owned by the Archaeology Department at the University of Sheffield with funding secured by Roger C.P. Doonan. The specimens used in Sections 5 and 6 were made by Vassilis Kilikoglou, National Centre for Scientific Research “Demokritos,” Greece. Liev Frahm assisted with their measurement in the test stand. For their analyses in Section 6 , the datasets were collected as a hands-on exercise by participants in the Marie Curie training course “Introduction to pXRF in Archaeology” held at the University of Sheffield in January 2013 and co-taught by me and Doonan, who indulged my suggestion that we conduct such a test as a component of our course. The course participants are sincerely thanked for their contribution to this study: Mainardo Asinelli, Lydia Avlonitou, Olivier Bonnerot, Andrea Ceglia, Andreas Charalambous, Elisavet Charalambous, Artemi Chaviara, Anastasia Cholakova, Ioannis Christodoulakis, Maria Dikomitou-Eliadou, William Gilstrap, Keith Haylock, Francesca Licenziati, Christina Makarona, Roberta Mentesana, Noémi Müller, Frederik Rademakers, Jessica Slater, Michael Smith, and Lente Van Brempt. Two of the four pXRF instruments that course participants used in Section 6 are owned by the University of Sheffield, and the other two were loaned for the course by Niton UK, thanks especially to John Hurley and Ken Granger. This research was also supported by the Department of Anthropology, Department of Earth Sciences, Electron Microprobe Laboratory, and Institute for Rock Magnetism at the University of Minnesota. Further support was provided by the Marie Curie Network FP7-PEOPLE-2010-ITN: New Archaeological Research Network for Integrating Approaches to Ancient Material Studies (NARNIA), which is coordinated by Vasiliki Kassianidou, Archaeological Research Unit, University of Cyprus. Doonan was leader for NARNIA Work Package 7 and also provided insightful comments on a manuscript draft that ultimately became Section 6 here. The editor and three anonymous reviewers are thanked for their helpful comments and critiques that improved the clarity of the final manuscript.
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- Field methods
- Obsidian sourcing
- Pokr Arteni
- Source characterization