Henry Wilhelm,Founder and Director of Research and PublicationsWilhelm Imaging Research, Inc., Grinnell, Iowa, U.S.A.Co-Authors:Ken BoydstonChief Engineer and Color ScientistMegaVision, Inc., Ventura, California, U.S.A.Joe UzielCurator and Head of Dead Sea Scrolls UnitIsrael Antiquities Authority, Jerusalem, IsraelShai HaleveiChief Photographer and Head of Multispectral CaptureIsrael Antiquities Authority, Jerusalem, IsraelHigh-resolution multispectral imaging provides periodic full-image area, non-destructive and zero-contactmonitoring over both short and very long periods of time of cultural heritage materials, including photographs, paintings, fabrics, documents, books, tapestries, and other works of artistic and historicimportance with very large data sets consisting of up to ten thousand or more discrete colorimetric data pointsfor the short-term and long-term monitoring of full-tonal-scale – generally nonlinear – colorimetric changes (including in the UV and IR regions), in a fully time-integrated manner, that may take place over time in thefull image area and in the support material (front and back). Multispectral imaging can accurately monitor rates of degradation of optical brightening agents (OBAs) and can quantify gradual yellowish or other stain formation in photographs, including albumen prints, polyethylene coated (RC) papers, and other materials.
Multispectral imaging provides the ability to monitor glazed works periodically during exhibition without the necessity of removing glass or plastic sheets from their frames while the works remain on the wall. Likewise, works housed in anoxic frames may be monitored over the long term without opening the frames. Irregularities in image deterioration and/or staining brought about by localized variations with photographic materials and their chemical processing, washing, contamination during drying, or as a result of selenium, sepia, gold, or other chemical toning treatments, coating and varnish layers, laminates, and other steps employed in the creation and finishing of the work, integrated with the inevitably non-uniform contact with mounting, framing, and storage materials over time, and the effects of exposure to non-uniform lighting, environmental and “micro-climate” temperature and relative humidity conditions, can be assessed and compared over long periods of time in all areas of an image – including within very small image details.
Representative times currently required for a MegaVision camera-based high-resolution capture of an object are:
1 minute and 16 seconds for 16 sequential image captures with 16 different waveband illuminants (with no filter wheel captures), with an integrated lux exposure of 0.12 lux/hour (equivalent to <10 seconds of display at 50 lux), and 3 minutes and 15 seconds for 26 sequential image captures with 26 different waveband illuminants (capture time includes 10 filter wheel captures for a more comprehensive OBA degradation analysis), with an integrated lux exposure of 0.33 lux hour (equivalent to <1 minute of display at 50 lux). High-resolution multispectral camera captures provide extremely accurate color images that are superior to RGB captures. These images can be used to automatically generate lower-resolution RGB images for cataloging, websites, publications, posters, and other uses. These high-resolution images can also readily be used to make color-accurate facsimile prints for exhibitions and study. Multispectral imaging employed as a routine part of the acquisition and accessioning process provides a “time-zero” set of high-resolution spectral data for every object that can then be used for very-long-term monitoring.
This presentation will consider the formidable technical challenges of very-long-term monitoring in the context of the now more than 2,000-year-old Dead Sea Scrolls in Israel, and the ongoing programs to systematically multispectrally capture each scroll and scroll fragment, monitor, and preserve the delicateparchment scrolls and scroll fragments. During the coming hundreds or many thousands of years into the future, every single part of a multispectral imaging system and the associated computers, software and data storage systems, calibration targets – and our understanding of color science itself – will repeatedly become obsolete and must be replaced with new systems. Strategies thatwill ensure a continued high degree of accuracy relative to the original measurements are proposed.
Without a comprehensive multispectral monitoring program, conservators and other institutional caretakers will have little or no quantitative data concerning what has actually been happening to their collections as they age over time, and with the understanding that comes with that quantitative information, of how degradation may be slowed or halted by changes in display and loan policies, by the use of humidity-controlled refrigerated and sub-zero freezer preservation, and by other means, some of which are yet to be developed.
References:- Henry Wilhelm, “Monitoring the Fading and Staining of Color Photographic Prints,” Journal of the American Institute for Conservation, Vol. 21, No. 1, Fall 1981, American Institute for Conservation (AIC), Washington, District of Columbia, U.S.A., pp. 49-64.
- JPL (Jet Propulsion Laboratory, Pasadena, California), “Conceptual Design of a Monitoring System for the Charters of Freedom,” Jet Propulsion Laboratory Publication 83-102, March 15, 1984. The Jet Propulsion Laboratory is under the jurisdiction of the California Institute of Technology, and is administered and funded by the National Aeronautics and Space Administration (NASA), a U.S. Government Agency that began operations in 1958.
- Douglas G. Severson (The Art Institute of Chicago), “The Effect of Exhibition on Photographs,” Topics in Photographic Preservation – 1986 (compiled by Maria S. Holden), Vol. 1, pp. 38-42, 1986. American Institute for Conservation Photographic Materials Group, American Institute for Conservation (AIC), Washington, District of Columbia, U.S.A. Slightly revised, the article was reprinted in Picturescope, Vol. 32, No. 4, Winter 1967, pp. 133-135.
- Alan R. Calmes, “Monitoring the U.S. Charters of Freedom by Electronic Imaging,” (U.S. National Archives and Records Administration, Washington, District of Columbia, U.S.A.), Proceedings of the International Symposium: Conservation in Archives, National Archives of Canada in conjunction with the International Council on Archives, Ottawa, Ontario, Canada, May 10-12, 1988, pp. 243-251.
- John McElhone (National Gallery of Canada), “Determining Responsible Display Conditions for Photographs,” presentation at The Centre for Photographic Conservation Conference ’92: The Imperfect Image: Photographs, their Past, Present, and Future, Windermere, Cumbria, England, United Kingdom, April 6–10, 1992.
- Henry Wilhelm, “Monitoring the Fading and Staining of Color Photographs in Museum and Archive Collections,”
pages 239-266 in Chapter 7, “The Permanence and Care of Color Photographs: Traditional and Digital Color Prints, Color Negatives, Slides, and Motion Pictures,” by Henry Wilhelm withcontributing author Carol Brower, Preservation Publishing Company, Grinnell, Iowa, U.S.A., 1993. - W.A. Christens-Barry, K. Boydston, F.G. France, K.T. Knox, R.L. Easton, and M.B. Toth, “Proc. SPIE, San Jose, CA, 7249(8), 1-10 (2009).
- Marc Kaufman, “Jefferson changed ‘subjects’ to ‘citizens’ in Declaration of Independence,” The Washington Post, July 3, 2010. “It took research scientist Fenella France [using a MegaVision Multispectral Imaging and Analysis System] weeks to pull out each letter until the full word became apparent.” “Finding Jefferson’s erased word is the library’s greatest accomplishment using its new technology, but several other projects are in progress. The imaging device, for instance, found thumb and fingerprints on the Gettysburg Address using infrared light, and library researchers are seeking to determine whether they are President Abraham Lincoln’s…” “[Library of Congress Preservation Director, Dianne van der Reyden] said the research and discoveries illustrate why it’s so important to keep and protect original documents. The erased ‘subjects,’ she said, could have been detected only from Jefferson’s original draft.
IMPORTANT NOTE: Because of word-count limits on the AIC Program website, this version of the abstract has been truncated. To download the full 12-page abstract, complete with twenty-five references and the authors’ biographies, please click on this link:
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