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Preserving History at the U.S. National Library of Medicine

Memorial Day prompts us to remember and honor those men and women who fought and died in the line of battle.  It is also an occasion to remember that history fades:  that the material which holds and conveys our knowledge, experiences, and memories—printed books and journals, hand-written documents, photographic images, films of various formats—are all subject to the laws of nature.

In this landmark year for the U.S. National Library of Medicine (NLM)—its 175th anniversary—its staff have been facing down nature through a project that looks to the next 175 years and beyond.  Engaging in the emerging field of forensic conservation—a cross-over application of forensic science and state-of-the-art analytical technologies—staff are seeking to protect and save for future generations one of the most important historical documents of the twentieth century:  the first summary of the genetic code, created by the American biochemist and 1968 Nobel Laureate, Dr. Marshall Nirenberg (1927-2010), whose papers the Library makes publicly available through Profiles in Science, the NLM’s premier digital manuscript project that celebrates twentieth-century leaders in biomedical research and public health.

Written in multiple blue-ballpoint pen inks on several sheets of 8 ½” x 11” paper taped together with pressure-sensitive tape, the Nirenberg genetic code chart records the author’s deciphering of the genetic code contained in DNA.  Here was the very discovery of how sequences of DNA—known as “triplets” —direct the assembly of amino acids into the structural and functional proteins essential to life. Dr. Nirenberg’s work ranks with that of Dr. James Watson and Dr. Francis Crick in our understanding of the genetic basis of life on earth.

Visual inspection of the chart reveals the impact of nature on the various inks, tape, and paper used by Dr. Nirenberg.  The inks show signs of color shifts and fading.  The tape has degraded to an oxidative state.  The paper has discolored.  A complete scientific analysis of the chart has therefore begun in order to insure its existence for future generations.  Fundamental to this analysis are certain understandings about color and color change.

Color is a complicated science because it is a human perception.  History shows it has puzzled humans since antiquity.  There are a number of color scales and models that attempt to shape the relationship between measured color and perceived color.  Quantifying color is desirable when assessing change in both separation and identification of the target sample, in this case the Nirenberg chart.

Analyzing color and color change in any document is a challenge using traditional spectroscopic analytical techniques.  Chromatography is a separation science that resolves individual components of color complexes.  Visible spectroscopy is an identification science that can classify chromaphore change—that is, change in that part of the molecule responsible for its color.  Additionally, the field of visible spectroscopy offers significant information about the progress of oxidation.  However, there are several limitations to each of these individual techniques.  Almost all non-destructive chromatographic and spectroscopic techniques depend on using a limited sample size.  It is the equivalent of trying to appreciate a masterpiece through a key-hole.

Conventional analytical approaches therefore limit a full-format document quantitative analysis of change.  Full-document analysis is a standard in forensic-document examination, but forensic analysis generally involves authentication, not broad format deterioration.  Conservation science is interested in the measurable extent of aging or more specifically fading as a result of oxidation that will provide the researcher some direction for protocol development.

NLM staff have therefore explored the use of Adobe Photoshop® for full document digital color analysis as a comprehensive companion to traditional analytical chromatography and spectroscopy to deconstruct document ink color change.  This approach to color analysis allows quantification of color change using the numeric red, green, and blue (RGB) channel model.  Consequently, color change can be quantified in total document format analysis.  Staff refer to this approach as “Adobe Photoshop® assisted spectral-chromatography.”  In this approach, the typical document copier/scanner behaves by analogy as a visible spectrometer coupled with Adobe Photoshop® software to assist in the chromatographic analysis.  The advantage of this approach is a non-destructive full-document, multiple-data point—or “multiplex” —deconstruction of color in precious historical documents.

This research holds great promise for the fields of conservation and preservation.  Today—nearly seventy years after the obvious commercial success and integration of the ballpoint pen into modern society—the tradeoff of its convenience is being discovered:  documents written in ballpoint pen ink are fading as the chemicals in ink react with document materials and their environments.  In the case of the Nirenberg chart, the very historical knowledge it holds is fading with time.  What steps are needed to mitigate this process?  Does the same fate of degradation await the millions—if not billions—of other twentieth-century documents composed with ballpoint pen ink, and not least the most precious of those documents in archives and libraries here in the United States and around the world?  The promise of answering these questions lies ahead as the cutting-edge medical heritage of the Nirenberg chart receives the evaluation, stabilization, and preservation it deserves for the benefit of generations whose lives will be affected profoundly by these early years of the genomic era.