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. There is often confusion between the terms anoxic and hypoxic. Anoxic refers to the complete removal of oxygen and for the Library (due to limitations of monitoring equipment) this is considered less than 0.5% oxygen. Hypoxia refers to reduced oxygen levels, below that of ambient air which is 21% oxygen.
Most recently, an anoxic encasement for the Buell Map was constructed and is now on display in the North Gallery of the Great Hall of the Jefferson Building. One challenge in the design of the encasement was to replace an oxygen sensor used for the previous encasement monitoring that was no longer commercially available. A prototype of the sensor was built, calibrated, and tested, and is currently in use for the monitoring of the interior conditions of the case.
The construction of the Buell Map encasement followed the success of the collaboration between, the Preservation Directorate and the National Institute for Standards and Technology (NIST) 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 goal of both projects was the successful design, fabrication, testing, and installation of an argon encasement to protect both rare and unique Library maps. The 40 ft. square Waldseemüller 1507 World Map still remains the largest such encasement manufactured to date, with the Buell encasement slightly less in dimensions. The requirements for both encasements were as follows:
- Create a sealed environment and passively maintain inert gas levels for at least 5 (Buell) and up to 20-25 years for Waldseemüller
- Provide capacity to monitor the maps by measuring and monitoring real-time environmental changes
- Meet preservation needs for long-term display of historic materials
- Accommodate changes in differential pressure caused by changes in barometric pressure
- Ability to move anoxic case unit
- Integrate monitoring with the Library's electronic and security infrastructure
- Accommodate size and weight limitations of encasements and historic building requirements
Left: Buell map before full installation of glass & frame.
Right: Lifting 600lbs of glass onto case.
Outcomes/Findings:
- 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: Waldseemüller encasement: Alcoa Foundation, Alcoa, Inc. and Solutia, Inc., Buell encasement: The Library acknowledges the support of Mr. David Rubenstein.
Acknowledgements: The National Institute for Standards and Technology was a full partner in these projects and provided invaluable expertise and assistance for developments and advances during both projects.
Update and Images:
April 2023: A joint working group of anoxic encasement users in the DC area (from Library of Congress, National Archives and Records Administration, and Smithsonian’s Museum Conservation Institute and National Museum of African American History and Culture) composed a second white paper highlighting important considerations users need to make before undertaking a low-oxygen encasement project. Access the white paper here.
December 2021: A joint working group of anoxic encasement users in the DC area (from Library of Congress, National Archives and Records Administration, and Smithsonian’s Museum Conservation Institute and National Museum of African American History and Culture) composed a white paper highlighting the historic trajectory of anoxic encasements in museum use. Access the white paper here.
October 2013: LC and NIST staff successfully design, construct, test, and install the Buell Map encasement for Public view.
June 2012: Fenella France presented “Defining Data Collection for Assessing and Monitoring Visual Storage Environments” at the Indoor Air Quality (IAQ) Conference, University College London (UCL), London, UK.
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.
