By DONNA URSCHEL
For many decades, details of the 1791 Pierre L’Enfant Plan of Washington, D.C.—one of the many treasures at the Library of Congress—had been obscured. A long-ago application of a varnish preservative had darkened the map’s surface. But today, thanks to special imaging techniques, the invisible streets and special locations, including the “President’s House” and “Congress’ House,” pop out.
Hyperspectral imaging, a process of taking digital photos of an object using distinct portions of the light spectrum, is revealing what previously could not be seen by the human eye.
In room 27 on the sub-basement level of the James Madison Building, fascinating details of our historical heritage are coming to light in the recently opened Optical Properties Laboratory. Operated by the Library’s Preservation Research and Testing Division (PRTD) in the Preservation Directorate, the lab contains a hyperspectral imaging system, an environmental scanning electron microscope (ESEM), equipment for optical-disc quality testing and a Fourier Transform Infrared Spectroscopy (FTIR) system.
The new lab enhances the Library’s capability to use nondestructive analytical techniques to track changes in optical properties of materials, helping conservators, curators and librarians extend the life of the collections. Along the way, many interesting details about the documents are revealed.
The Optical Properties Lab is one of three new labs in the Preservation Directorate. Two more will open in the Madison Building in 2010, the Chemical and Physical Properties laboratories. The new equipment and redesigned space will bring the 30-year-old science labs of the Preservation Directorate into the 21st century.
“Other libraries in the United States and around the world depend upon the cutting-edge capabilities of the Library of Congress preservation labs. I invested in updating the labs to continue Preservation’s important legacy,” said Deanna Marcum, associate librarian for Library Services. “Current analytical technology allows us to do more now with less. More sensitive analysis can now be undertaken with less sampling, less preparation, in less time and with less instrumentation and waste.”
Marcum continued, “I’ve been gratified with the discoveries and advances the Optical Properties Lab has made in the few short months it has been open, revealing hidden writing and lost text, giving new insight into the Library’s Top Treasures.”
Recent imaging of the Library’s handwritten draft of the Gettysburg Address (the Nicolay copy) illuminated a thumbprint on the front and three fingerprints on the back, as if someone had been holding the document while reading it. Was it Abraham Lincoln?
Fenella France, a PRTD scientist who heads up the hyperspectral imaging, discussed the recent discovery. “We had noticed a darkened area on the document. We looked closer and the fingerprints came into focus,” France said. “It was a goosebump moment.”
France then tried to track down information on Lincoln’s fingerprints but could not find anything for comparison. She hopes someday to conduct hyperspectral imaging on other Lincoln documents.
Hyperspectral imaging looks at materials via narrow wavelength band regions of the light spectrum, from ultraviolet through visible to infrared. The images are captured and digitally combined with or subtracted from each other to reveal details invisible to the naked eye. The results inform scientists on how to better preserve treasured items.
The document detective work also enhances historical details.
On the 1791 L’Enfant Plan of Washington, imaging reveals a traffic circle drawn at 16th and K Streets that had been erased. Did L’Enfant make a drawing mistake or was he seriously considering a circle there?
Occasionally the Library will use its imaging system to assist other agencies. Last fall, the Library was part of a forensic document examination team for the National Archives and Records Administration that studied two pages of handwritten notes of H. R. Haldeman, chief of staff for President Richard M. Nixon. These were the notes taken on the day that Nixon lost more than 18 minutes of conversation on his office tapes. Results will be released in 2010.
The environmental scanning electron microscope (ESEM) is another system that reveals details invisible to the naked eye. The microscope produces images at a very high magnification, up to 100,000 times.
As with hyperspectral imaging, ESEM is a non-invasive method. An entire document can be placed in a chamber of the microscope, which maintains proper environmental temperatures, humidity and pressure. A high-energy beam of electrons scans the document and produces digital images and a chemical analysis reading.
Jennifer Wade, a PRTD scientist who heads up ESEM imaging, said the electron microscope yields a digital image with a three-dimensional appearance that reveals an item’s surface structure. In addition to an image, a spectrum is produced with peaks that represent the chemical elements. The higher the peak, the more that element is contained in the material.
In a current project, Wade is using ESEM to analyze ungilded daguerreotypes. Daguerreotypes were the first form of photography, introduced in France in 1839. Until 1841, daguerreotype plates were not gold-coated or gilded, resulting in surfaces that are uniquely fragile and difficult to study or treat. The Library holds more than 725 daguerreotypes, eight of which are ungilded. One of the eight is the first American photographic self-portrait, an 1839 image of Robert Cornelius.
The Library commissioned a company to create four daguerreotype plates that mimic the ones created in 1839. With these model plates, Wade can use ESEM to learn how the plates are damaged and corroded and then work with conservators who develop treatment, storage and housing guidelines.
The Optical Imaging Lab also contains a Fourier Transform Infrared Spectroscopy (FTIR) system. Like SEM, FTIR looks at objects at a microscopic level and reveals the chemistry.
“Saving the human record has entered a new phase,” said Dianne van der Reyden, director of the Preservation Directorate. “And we are very pleased that our scientists, and new science labs, headed by PRTD Chief Eric Hansen, can help conservators and others meet the challenge ahead.”
Donna Urschel is a public affairs specialist in the Public Affairs Office.