A Jet Propulsion Laboratory researcher has used modern infrared imaging technology to reveal previously invisible details on fragments of the Dead Sea Scrolls.

In the project, Dr. Gregory Bearman used a solid-state sensor and computer image-processing to examine fragments from the scrolls, a collection of 2,000-year-old manuscripts found in caves on the Dead Sea.

"This approach allows us to see details that are invisible using traditional photography on film," said Bearman. "Archeology is just beginning to learn about digital imaging technology, and it should prove to be a very powerful tool."

Bearman describes his work in a paper presented November 20 at a meeting of the American Academy of Religion/Society of Biblical Literature in Washington, D.C.

Co-authors working with him included Dr. Bruce Zuckerman of the University of Southern California, Ken Zuckerman of West Semitic Research and Joseph Chiu of the California Institute of Technology. Also collaborating on the project was the Ancient Biblical Manuscript Center in Claremont, Calif.

Discovered in the 1940s and 1950s, the Dead Sea Scrolls include thousands of fragments in Hebrew, Aramaic and Greek written on sheepskin and other materials. The scrolls encompass a variety of religious literature and are believed to have been left by a Jewish community living near the Dead Sea from about the 2nd century B.C. to the 1st century A.D.

Because of their great age and exposure to elements after discovery, some of the scrolls have deteriorated and are mostly impossible to read with the naked eye. The black ink typically cannot be distinguished from the blackened parchment.

Scholars for many years have used film-based infrared photography as a way of revealing the scrolls' invisible characters. That technique, however, is limited by the nature of infrared film.

"A camera using infrared film with a conventional filter will see continuously from the visible spectrum out into the infrared spectrum," Bearman explained. "That has proven successful in revealing some of the scrolls' content, but in some cases text is still not visible.

"What digital infrared imaging allows us to do is to look at the scrolls in a narrow wavelength band," he added. "In some cases this reveals detail which a film-based camera looking at a broader wavelength spectrum cannot see."

Infrared films using a conventional filter, for example, are sensitive to light from the red end of the visible spectrum -corresponding to a wavelength of about 700 nanometers -- out into the infrared range to 900 nanometers.

"In our work we found that the parchment of the Dead Sea Scrolls is more reflective than the ink in the range of about 800 to 1,000 nanometers, which explains why cameras using those films and filters have been fairly successful," Bearman said.

"In some cases, however, text remains obscured when imaged in this wavelength range," he added. "We may be able to see it, however, by using a charge-coupled device (CCD) digital camera that looks at the document in the 1,000- to 3,000-nanometer range, much farther in the infrared than film."

That was the case when Bearman and his colleagues used their imaging equipment on a Dead Sea Scrolls fragment lent by the Getty Conservation Institute, from a document called the Genesis Apocryphon.

To the naked eye, the fragment appears to have been completely ruined over time, with any vestige of text obliterated. Film-based infrared photography, however, reveals a series of largely illegible characters in one portion of the fragment.

When the researchers imaged the fragment with a CCD camera in the 900- to 1,000-nanometer wavelength range, they obtained higher contrast images than is possible with film, said Bearman.

"On part of the fragment, the text is covered by a parchment flap that remained stuck when the scroll was unrolled," he added. "By looking at this portion with a CCD camera in the 1,000- to 3,000-nanometer spectral range, we can make out another word of text which is invisible to either film-based or CCD imaging in the 800- to 1,000-nanometer range."

In addition, the researchers used their equipment to examine several Greek papyri -- text written on strips cut from the stems of marsh plants -- that are more recent than the Dead Sea Scrolls.

According to Bearman, his team used an "off-the-shelf" infrared camera using a CCD sensor, combined with a frame grabber and computer workstation.

Further archeological research would be enhanced, he said, by building a system that would optimize imaging sensitivity at selected wavelengths.

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