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X-ray Technology Sheds Light On Ancient Stone Inscriptions

August 17, 2005
Cornell University
Cornell University scientists and humanists have teamed up to demonstrate a novel method for recovering ancient text by zapping and mapping worn inscriptions using X-ray fluorescence imaging and the Cornell High Energy Synchrotron Source. XRF is a nondestructive chemical analysis technique that is widely used in geology, archaeology and materials science.

This is a scan of a group of letters on CIL VI 12139. The top panel is the photographic image. The middle panel is the iron fluorescence; while there is iron fluorescence visible, it becomes very weak in areas that have been significantly worn away. The bottom panel is lead fluorescence. Even in areas that have been significantly weathered, the fluorescence is strong enough to clearly read the text.
Credit: Image courtesy of Cornell University

ITHACA, N.Y. -- In an unusual collaboration among scientistsand humanists, a Cornell University team has demonstrated a novelmethod for recovering faded text on ancient stone by zapping andmapping 2,000-year-old inscriptions using X-ray fluorescence (XRF)imaging.

The research, carried out at the Cornell High EnergySynchrotron Source (CHESS), applies a nondestructive chemical analysistechnique widely used in geology, archaeology and materials science.

"X-rayfluorescence imaging has the potential to become a major tool inepigraphy [the study of incised writing on various surfaces, includingstone]," said Robert Thorne, professor of physics and co-author of anarticle in a German journal titled "Recovering Ancient Inscriptions byX-ray Fluorescence Imaging." "It's just so much more powerful thananything that's been used in the past."

The article describes thefirst successful application of XRF imaging to the study of ancientstone inscriptions between 1,800 and 2,400 years old. It will bepublished in August in Zeitschrift fur Papyrologie und Epigraphik(journal for papyrology and epigraphy) , one of the world's leadingjournals on ancient texts. The discovery could herald an importantbreakthrough in the study of ancient cultures.

"Inscribed textsare of considerable interest to the linguist and philologist," saidKevin Clinton, Cornell professor of classics, a co-author of thearticle. "Because of the information contained in them, they areinvaluable sources for the historian, archaeologist, art historian andevery student of institutions and life in the ancient world."

Thefindings result from a multidisciplinary effort among Cornell's facultyand graduate students in the departments of Physics, Applied Physicsand Classics, as well as members of CHESS -- where the XRF imagingexperiments were conducted.

"A synchrotron is a high-intensityX-ray machine," said Donald Bilderback, associate director of CHESS anda Cornell applied physics professor, also a co-author. "It's over amillion times more intense than the tube X-ray sources used in medicalimaging and in standard XRF analysis."

At CHESS, a high-energy,ultra-intense X-ray beam is produced by the electrons and positronsthat circulate inside the synchrotron at almost (99.9999995 percent)the speed of light. This X-ray beam was fired at three inscribed marblestones loaned from Columbia University's Butler Library. Just as with afluorescent lighting tube in which higher energy ultraviolet light isconverted to lower energy visible light by atoms coating the insidesurface, atoms illuminated near the surface of the stone emitted lowerenergy fluorescent X-rays. By using a spectrometer to analyze theenergies and intensities of these rays, the concentrations of traceelements in the stone were determined. Because the synchrotron's X-raybeam was so intense, these trace-element measurements could be quicklyrepeated as the stone was scanned back and forth in the beam, producinga map or image of each element's concentration.

The choseninscriptions -- one in Classical Greek and two in Latin -- eachpresented different levels of wear. XRF imaging detected minute amountsof iron, zinc and lead in the inscribed regions, among other elements.Iron chisels were commonly used to inscribe the stones, and the letterswere usually painted with pigments containing metal oxides andsulfides. These may account for the iron and lead, but the source ofthe zinc is a mystery. In the most worn stone, the trace elementsmeasured by XRF clearly revealed the contours of the original letters,even where they were no longer visible to the eye. For modestly wornstones, XRF imaging will help to decipher texts and may provide newinformation on how the inscriptions were made.

"This meansrestoring thousands of stones, including, possibly, part of the lawcode of Draco," said Clinton. Draco was a seventh-century Athenianpolitician who codified the law of Athens. "It applies to practicallyany kind of public document you can think of, including many laws,decrees, religious dedications and financial documents."

What'smore, an XRF device can be made portable (though collecting the datawill be significantly more time consuming than at a synchrotron X-rayfacility).

A brief history of a collaboration

In theMediterranean alone, there are an estimated half-million Greek andLatin inscriptions on stones in various states of decay and legibility.The collaboration that led to XRF restoration grew from conversationsbetween Clinton and his colleague Nora Dimitrova, a Cornellpostdoctoral associate in classics. They asked Cornell physicistBogomil Gerganov if there were any new scientific methods fordeciphering worn text. While teaching at the Weill Cornell MedicalCollege in Doha, Qatar, Gerganov raised the issue with Thorne, who wasvisiting Doha in March 2003. Thorne, also physics course director forthe pred-med program in Qatar, was familiar with Bilderback's successin applying XRF imaging to paintings and immediately saw its potentialfor inscriptions.

Back in Ithaca, Thorne met with Clinton,Dimitrova, Bilderback and John Hunt, an expert in microanalysis at theCornell Center for Materials Research. A preliminary measurement byBilderback and his research associate Rong Huang in March 2004 gaveencouraging results. Physics graduate student Judson Powers then joinedthe team. With help from CHESS staff scientist Detlef Smilgies, Powerstook over the lion's share of the work and is first author on theteam's publication.

The only thing missing: some ancientinscribed stones. No problem. Clinton and Dimitrova had identifiedsuitable samples at the Butler Library and contacted Columbia colleagueRoger Bagnell, who arranged for a loan.

By July 2004 the team had proven the principle of XRF imaging in the field of epigraphy.

Thorne finds no small amount of wonder in the process.

"Herewe are reading stones that were inscribed with iron chisels 100generations ago, using invisible rays that are produced by relativisticanti-matter," he said, referring to the synchrotron's role in theexperiments.

These first experiments were supported by Cornell'sOffice of the Vice Provost for Research and by the Department ofClassics with additional support from the National Science Foundation(NSF). The collaboration recently received a grant from the Samuel H.Kress Foundation to continue the work. CHESS is supported by the NSFand the National Institutes of Health.

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