Imaging the Dead Sea Scrolls for conservation purposes
The Israel Antiquities Authority (IAA) recently decided to employ modern digital imaging and imaging spectroscopy to study the Dead Sea Scrolls. High-resolution color and IR images will be provided to text scholars for use in transcription and translation. Stored at the ideal temperature and humidity in an environmentally controlled vault at the Israel Museum in Jerusalem, the scrolls must occasionally be removed. Traditionally, scholars work with film negatives on a light box, removing the actual fragments only when the negatives are insufficient to their needs. However, exposure to environmental changes may cause the scrolls to degrade. This new project is driven by two main goals, both of which rely heavily on modern imaging technology. The imaging project will create a complete and accessible online database of high-resolution images that will eliminate the need for physical handling of the scrolls. In a concurrent prospective study, imaging spectroscopy will be applied to selected scrolls aimed at detecting changes in the reflection spectra as potential markers of parchment deterioration. This is a large project because there is a lot of original material to image.
A better name for the scrolls may be the ‘Dead Sea Fragments,’ since the collection comprises few comparatively intact scrolls. Rather, 15,000 fragments are mounted on about 1500 inventory plates. All have to be imaged in at least two modes and then entered into a database to track the images and link them with the vast existing literature, catalogs, and visual material.
Following their discovery in 1948, the scrolls were photographed in the early 1950s, primarily using IR film and Kodak filters. It has long been known that IR imaging dramatically improved legibility of the scrolls that were impossible to read with the naked eye. In 1993, spectral imaging explained why IR imaging of the scrolls was successful,1 which paved the way to improve and simplify imaging techniques. Changes in the relative reflectance of the ink and parchment were responsible for the decline in legibility (i.e., deterioration of the contrast between ink and parchment). As the parchment darkens the contrast decreases and it turns into the ‘finding the black cat at midnight’ problem. It is unknown why the parchment reflectance changes with time. For monitoring purposes the IAA will repeatedly, perhaps biannually, image a set of test fragments at visible and near-IR wavelengths for analysis. The spectral data in the visible will monitor changes in color2 while the full range up to 1000nm will reveal any additional changes.
In the last two weeks of August 2008, the IAA conducted a two-week pilot imaging project. Using borrowed and leased equipment we set up three imaging stations in an ISO-compatible (ISO: International Organization for Standardization) dedicated room at the Israel Museum across the hall from the scrolls' environmental vault (see Figure 1).
The project will have three imaging stations. High-resolution color imaging using a large-format digital back (such as the PhaseOne P45) will deliver a 39 megapixel image. The field of view is ~ 8×11in.2, which allows imaging of most plates at 600 dots per inch in one shot. Concurrent IR imaging will facilitate improved text legibility. Imaging at a single wavelength longer than 900nm provides excellent results,1 so there is no need for further spectral imaging. Illumination will be provided by 940nm LEDs. The camera is a monochrome version of the PhaseOne P45 without the Bayer filters. The high-resolution digital back is necessary to adequately resolve the text. The technology choice for spectral imaging has yet to be made. A Cambridge Research and Instrumentation Inc. 650–1100nm Nuance multispectral-imaging system was used in the pilot project.
The project will also develop the use of spectral imaging combined with spatially modulated illumination to measure the parchment's water content. Humidity is one of the most significant drivers of parchment degradation. If it is too dry, the parchment dries, shrinks differentially, and then tears. On the other hand, if the parchment is too humid or wet, the collagen will turn to Jello. We have collaborated with a research group at the University of California (Irvine) to combine spectral imaging with a method that separates scattering from absorption as photon-loss mechanisms so that Beer's law is applicable. This has been applied to tissue and skin, for example, to measure edema. Since parchment is, after all, skin, these approaches should be extensible to measure and map the water content.
We have applied similar imaging to a pottery shard (ostracon) with the oldest-known Hebrew inscription.3 The shard, comprising five lines of text, dates from approximately 3000 years ago. It was excavated in July 2008 and partially imaged during the pilot project. The imaging revealed and clarified the text, prompting the IAA to bring the ostracon to the USA in November 2008 for additional imaging.
The pilot imaging project was performed in collaboration with Simon Tanner (Kings College Digital Consultancy), Tom Lianza (Xrite) and Julia Craig-McFeeley (Oxford University). Simon Tanner and the author of this article serve on the IAA-established international steering committee for this project.
Until his recent retirement, Gregory Bearman developed imaging instrumentation at NASA's Jet Propulsion Laboratory (California Institute of Technology). He was a pioneer in applying modern imaging technology to archaeology and has worked with the IAA since 1994.