X-Ray Fluorescence Investigations of Ancient
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X-RAY FLUORESCENCE INVESTIGATIONS OF ANCIENT GREEK AND LATIN EPIGRAPHS A Thesis Presented to the Faculty of the Graduate School of Cornell University in Partial Fulfillment of the Requirements for the Degree of Master of Science by Judson Albert Powers January 2008 c 2008 Judson Albert Powers ALL RIGHTS RESERVED ABSTRACT Many ancient Greek and Latin epigraphs, once clear text on limestone and marble, have weathered and worn over the course of many centuries so that the words written on them are no longer legible. X-ray fluorescence, a common non- destructive chemical analysis technique, is extended to synchrotron-based X-ray fluorescence imaging, with which we can map the relative concentrations of many elements near the surface of a stone epigraph. We investigate the application of X-ray fluorescence imaging to these epigraphs. Initial results show an association between fluorescence intensity from trace elements near the surface of an epigraph and the presence of a glyph carved in the stone. Further, it is demonstrated that mapping this fluorescence intensity can, in some cases, improve legibility of the text beyond the capabilities of the unaided eye. Further investigations explore in more detail the usefulness of different trace elements for imaging text, potential origins of these trace elements, fluorescence intensity effects associated with the physical topography of the stone, and the application of statistical analysis techniques to X-ray fluorescence imaging data. We also apply our methods to an epigraph of uncertain provenance, demonstrating that the evidence provided by X-ray fluorescence indicates that it is a modern copy of another epigraph. BIOGRAPHICAL SKETCH Judson Powers began his studies in the fall of 1999 at Clemson University in Clemson, South Carolina. In 2003 he earned a Bachelor’s of Science in Computer Science and a Bachelor’s of Science in Physics, with departmental and general honors recognition from the Calhoun Honors College. During this time, he was involved in theoretical physics research under Dr. Joseph R. Manson, developing computer simulations of high-energy ion-surface scattering. This work was done in conjunction with Dr. Chad E. Sosolik’s experimental ion-surface scattering research under Dr. Barbara H. Cooper at Cornell. Judson also spent three months in the experimental labs of Prof. Dr. Karl-Heinz Reider and Prof. Dr. Saw-Wai Hla at the Freie Universit¨at in Berlin. Judson began his graduate studies in Cornell University’s Department of Physics in the fall of 2003, joining Dr. Robert E. Thorne’s research group late in the spring of 2004. Since, he has investigated the application of X-ray fluorescence imaging to ancient Greek and Latin limestone and marble epigraphs at the Cornell High Energy Synchrotron Source. iii ACKNOWLEDGEMENTS This work has been supported by the Office of the Vice Provost for Research and the Department of Classics at Cornell University, by the National Science Foun- dation (DMR 04-05500) and by the Kress Foundation. This work is based upon research conducted at the Cornell High Energy Synchrotron Source (CHESS) which is supported by the National Science Foundation under award DMR-0225180. I would like to acknowledge the support and assistance of the CHESS staff, including Arthur Woll, who allowed us use of his large scanning stage, Don Bilder- back, who first taught me about X-ray fluorescence, Rong Huang, who wrote and demonstrated his MCASPEC software, Darren Dale, who introduced me to PyMCA, and Detlef-M. Smilgies, who is responsible for most of the configuration, tuning, and maintenance of our experimental equipment and who has provided many invaluable ideas and insights. Kevin Clinton and Nora Dimitrova in the Cornell Classics Department have provided a wealth of information about the an- cient world and epigraphy. I have likewise received valuable information, advice, and assistance from John Chiment (Simple Interest), John Grazul (Cornell Cen- ter for Materials Research, CCMR), John Hunt (CCMR), Arthur Lembo (Cornell Crop and Soil Sciences), and Richard Stone (Metropolitan Museum of Art). A number of institutions have been so kind as to lend us valuable and irreplace- able artifacts: the Francis Lehman Loeb Art Museum at Vassar College (curator, James Mundy), the Department of Classics at Johns Hopkins University (curator, Eunice Maguire), the Department of Classics at New York University (chair, Prof. Michael Peachin), the Butler Library at Columbia University (via Prof. Roger Bagnall), and the Princeton Museum of Art at Princeton University (curator, J. Michael Padgett). iv TABLE OF CONTENTS BiographicalSketch.............................. iii Acknowledgements .............................. iv TableofContents............................... v ListofTables ................................. vii ListofFigures................................. viii 1 X-ray fluorescence recovers writing from ancient inscriptions 1 1.1 Introduction............................... 1 1.2 Experiment ............................... 2 1.2.1 X-rayfluorescence. .. .. 2 1.2.2 Experiment ........................... 3 1.2.3 Inscriptions ........................... 5 1.3 Results.................................. 9 1.3.1 CIL VI35066.......................... 9 1.3.2 IG II2 1969 ........................... 12 1.3.3 CIL VI12139 .......................... 14 1.4 Discussion................................ 17 1.5 Summary ................................ 19 2 X-ray fluorescence imaging analysis of ancient Greek and Latin epigraphs 21 2.1 Introduction............................... 21 2.2 GreekandLatinEpigraphs. 22 2.2.1 Types of epigraphs and their production . 22 2.2.2 Marble.............................. 24 2.2.3 Weathering, encrustation, and patinas . 24 2.2.4 Pigments ............................ 27 2.3 Method ................................. 28 2.4 PreviousFindings............................ 30 2.5 EpigraphsExamined .......................... 34 2.6 ElementsPresent ............................ 36 2.7 PresenceofTin ............................. 39 2.8 Trendsintraceelements . 41 2.9 Originofelements............................ 42 2.10 Correlation of calcium to inscribed text: two-detectordata ..... 43 2.11 Two-detectordata . .. .. 45 2.12 Principal components analysis . 51 2.13Conclusions ............................... 54 v 3 X-ray fluorescence imaging analysis of epigraph provenance 57 3.1 Introduction............................... 57 3.2 Method ................................. 59 3.3 Results.................................. 61 3.3.1 X-rayfluorescencespectra . 61 3.3.2 ComparisontootherXRFspectra. 65 3.3.3 Calcium fluorescence masking by trace elements . 68 3.3.4 X-rayfluorescenceimaging. 70 3.4 Discussion................................ 70 3.5 Conclusions ............................... 75 4 Principal components analysis versus two-detector measurements for X-ray fluorescence imaging of ancient marble epigraphs 77 A Equipment and setup at CHESS 81 A.1 Scanningstage ............................. 81 A.2 X-raydetector.............................. 83 A.3 In-hutchvideocameras. 83 A.4 Ionmonitors............................... 84 A.5 Beam-definingslits ........................... 84 A.6 Inhibitsignal .............................. 85 B Data Collection at CHESS 86 B.1 Preliminary measurements . 86 B.2 Per-epigraph setup and measurements . 86 B.3 Single-pointspectra. 87 B.4 Meshscans ............................... 89 B.5 In-hutchimagecapture. 90 C Acquired data 92 C.1 SPECoutput .............................. 92 C.2 Coordinates ............................... 94 C.3 MCAdatainMATLAB ........................ 95 D Principal Components Analysis 97 E Concentration and layer thickness estimation 100 F Data analysis software 106 F.1 MCASPEC ...............................106 F.2 PyMCA .................................106 F.2.1 Dataformat........................... 107 F.2.2 Capabilities ........................... 108 Bibliography 109 vi LIST OF TABLES 2.1 X-ray fluorescence data for elements of interest. ..... 31 2.2 Foreground and background element concentration in the epigraphs examinedat30keV. .......................... 38 2.3 Foreground and background element concentrations in the epigraphs examinedat17keV. .......................... 38 2.4 Trace element concentrations in JHU 1156b. .. 39 2.5 Qualitative association of fluorescence intensity with presence of inscribed text in single-element XRFI maps. 42 3.1 Approximate thickness of a trace element layer necessary to produce the observed fluorescence in the uninscribed background of the stone. 65 3.2 Calcium and common trace element fluorescence intensities for the NYU epigraph and six ancient Latin epigraphs. 66 3.3 Fluorescence intensities of less-common trace elements for the NYU epigraph and six ancient Latin epigraphs. 67 vii LIST OF FIGURES 1.1 CIL VI35066,photographicimage.. 6 1.2 IG II2 1969,photographicimage. 7 1.3 CIL VI12139,photographicimage.. 8 1.4 X-ray spectrum from an inscribed point and an uninscribed point on CIL VI35066............................. 10 1.5 The letter ‘D’ on the third line of Fig. 1.1, CIL VI 35066: optical image, iron fluorescence, and calcium fluorescence. .. 11 1.6 An intentionally erased area on CIL VI 35066, imaged optically and usingironfluorescence. 12 1.7 X-ray spectrum from an inscribed point and an uninscribed point on IG II2 1969.............................. 13 1.8 A letter Σ on IG II2 1969: optical image, iron fluorescence, calcium fluorescence. .............................. 14 1.9 X-ray spectrum from an inscribed point and