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The Declaration of Independence, the Constitution, and the Bill of Rights, collectively known as the Charters of Freedom, are on permanent display at the National Archives in Washington, D.C. In 1951 the Charters of Freedom were encased in helium-filled glass and metal cases built by the National Institute of Standards and Technology (NIST, formerly NBS). An examination in 1995 showed signs of deterioration in the encasements' glass; experts at the National Archives and NASA determined that the humidity in the cases was too high, causing alkali ions in the glass to dissolve and leave a white residue. Scientists at NASA and NIST recommended new high tech cases that incorporated pressure, temperature, and humidity sensors to protect the delicate parchment on which the Charters of Freedom were written.
As part of a major renovation of the National Archives Building that began in February 2000, the Charters of Freedom were removed from their original encasements, and reencased in new airtight containers made of aluminum, titanium, and glass. The new encasements were filled with argon gas to provide an inert atmosphere.
The argon gas that fills the encasements was humidified to a water partial pressure of 903 Pa (5.50 °C dewpoint) using the LI-610 Portable Dew Point Generator. The LI-610 was also used to calibrate humidity sensors installed in the encasements.
When the National Archives Rotunda reopened in September 2003, all four pages of the U.S. Constitution were displayed for the first time, along with the Declaration of Independence and the Bill of Rights.
LI-COR is proud to have had a small part in preserving these American treasures. More information about the Charters of Freedom and the re-encasement project can be found at the following link: http://www.archives.gov/national_archives_experience/charters/charters.html