NIST built two prototype encasements, which were tested extensively to evaluate the design and to analyze the performance and integrity of each component. The prototypes now serve as the back-ups that the National Archives hold in reserve, just in case.
NIST experts on pressure testing, leak rates, and chemical analysis went to great lengths to make certain that the new encasements met NARA's demanding performance requirements. For example, they calibrated the pressure sensors and specified the components of the equipment system that purge the encasements of air and fill them with humidified argon. NIST researchers also developed an extensive leak testing protocol that is used to test the integrity of the primary seal. This same prescribed procedure may be used by NARA staff to test the seal periodically after installation of the documents.
Before installation of the charter pages, all encasements underwent full-system tests. In all tests, seal performance far exceeded the design requirement.
NIST also conducted studies to determine whether the encasement glass could withstand abrupt and large changes in atmospheric pressure. The prototype encasements were subjected to wide swings in pressure until the glass finally broke. "There are no known ways," researchers concluded, "that the encasements would see the level of pressure difference causing glass failure, except due to a gross error. . ."
As the encasements were completed, they were shipped in special containers to NARA, where final testing and installation of the Charter pages was done. Several steps in the process are shown here:
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