Background: Oxygen promotes the deterioration of organic materials such as paper, parchment, and organic-based media including inks and other colorants. This deterioration is often visible as yellowing, embrittlement, and color fading. Anoxic encasement is one option for reducing oxygen exposure and related deterioration. Oxygen is removed from storage or display cases by displacing it with an inert gas such as nitrogen or argon. A good seal that can maintain interior case conditions depends on advanced case construction, materials, and design. The Library of Congress has researched, designed, and used anoxic encasements since the 1970's.
Most recently, the Preservation Directorate and the National Institute for Standards and Technology (NIST) collaborated to design, fabricate, and install an oversized argon encasement for the Library's Waldseemüller 1507 World Map, the only surviving copy of the earliest known map that names the land mass of America. This three-year project culminated in December 2007 with the permanent installation of the map in a near oxygen-free environment to mitigate the deleterious effects of long-term display.
In the 1990s, the Preservation Directorate created anoxic cases for five Library treasures, including two drafts of the Gettysburg Address, the rough draft of the Declaration of Independence, the Virginia Declaration of Rights, and the L’Enfant Plan of Washington, D.C.
Ongoing research and experimental design with new materials promise to improve the performance of anoxic cases. Leakage and performance testing of cases and sensors is an ongoing program in the Preservation Research and Testing Division.
Contributing Study: NIST Encasement protecting “America’s Birth Certificate”
Project Description: The final goal of the project was the successful design, fabrication, testing, and installation of an argon encasement for the 40 ft square Waldseemüller 1507 World Map, which is the largest such encasement manufactured to date. The requirements were as follows:
- Create a sealed environment and passively maintain inert gas levels for 20-25 years
- Provide capacity to monitor the map by measuring environmental changes
- Meet preservation needs
- Accommodate changes in differential pressure caused by changes in barometric pressure
- Ability to move anoxic case unit
- Integrate with the Library's electronic and security infrastructure
- Accommodate size and weight limitations
- The encasement frame was specially designed and engineered from a single block of aluminum and fitted with high-grade o-rings to create a hermetic seal and reduce oxygen infiltration.
- Constant monitoring of the encasement confirms it maintains a stable passive environment. Sensors monitor the differential pressure, oxygen level, temperature, and relative humidity in the encasement.
- Testing and monitoring over the first year confirmed minimal infiltration of oxygen into the encasement for a 29-year seal.
- The encasement system receives scheduled calibration and testing of sensors.
Support: Alcoa Foundation, Alcoa, Inc. and Solutia, Inc.
Acknowledgements: The National Institute for Standards and Technology was a full partner in this project and provided invaluable expertise and assistance for this project.
Update and Images:
March 2009: Dr. Fenella France presented a paper, “‘In and Out Air Strategies’ From Climate Change to Microclimate: Library, Archives and Museum Preservation Issues,” at the International Federation of Library Associations conference, Bibliothèque nationale de France, Paris.
April 2008: Elmer Eusman presented a paper at the American Institute of Conservation Annual Meeting in Denver, relating the activities surrounding the design, fabrication and installation of the Waldseemüller 1507 World Map in its new encasement.
July 2008: Dr. Fenella France gave a presentation at the Summit of Research Scientists symposium at the Library of Congress on the long-term monitoring and current status of anoxic cases at the Library of Congress.