Anoxic encasements
Background: Oxygen can cause yellowing, embrittlement and fading of organic materials such as maps, manuscripts and other documents. The Library of Congress has designed and employed anoxic encasements for select treasures to reduce the effects of oxidation since the 1970’s. Oxygen is removed from within the cases by displacing the oxygen with inert gas such as nitrogen or argon. Oxygen is prevented from infiltrating the cases by hermetic sealing and advanced case construction, materials and design.
Most recently the Preservation Directorate and the National Institute for Standards and Technology collaborated to design, fabricate, and install an oversized argon encasement for the Waldseemüller 1507 World Map, the only surviving copy of the map that names America for the first time. This three-year project culminated in the final installation of the map in December 2007 in a virtually oxygen-free environment, which will improve the longevity of this priceless artifact.
Contributing Study: http://www.nist.gov/public_affairs/releases/waldseemuller/waldseemuller.html
Project Description: The final goal of the project was the successful design, fabrication, testing, and installation of an argon encasement for the 40 square feet Waldseemüller 1507 World Map. The challenges were attributable to the fact that it is the largest such encasement manufactured to date. The requirements were as follows:
- Create and maintain a 20 to 25 year sealed environment, passively sustaining inert gas levels
- Provide capacity to monitor the map by measuring environmental changes
- Maintain levels of inert gas passively to achieve a 20-25 year seal
- Accommodate changes in differential pressure caused by changes in barometric pressure
- Have the ability to be mobile
- Be lined to LC electronic and security infrastructure
- Be constructed of high performance materials to meet preservation needs
- Accommodate size and weight limitations
Outcomes/Findings:
- A stable passive system is maintained and sensors monitor the differential pressure, oxygen level, temperature, and relative humidity in the encasement.
- A specially designed and engineered case made of a single block of aluminum was fitted with high-grade o-rings to create a hermetic seal and reduce infiltration of oxygen into the case.
- Testing and monitoring over the first year has confirmed the minimal infiltration of oxygen into the encasement and proven that the encasement is maintaining a 29 year seal due to the current o-ring configuration and high quality case materials, design and construction.
- Daily assessment of the case ensures a stable passive environment with scheduled calibration and testing of sensors on the encasement undertaken.
Support:
- Alcoa Foundation
- Alcoa, Inc.
- 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:
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.