February 1999
Fact Sheet: New Encasements for the Charters of Freedom
The Declaration of Independence, the Constitution and the Bill of Rights (on permanent display at the National Archives in Washington, D.C.) have guaranteed the rights and freedoms of Americans for more than 200 years. Since 1951, these great documents -- known collectively as the Charters of Freedom -- have been preserved in helium-filled cases created by the Commerce Department's National Bureau of Standards, predecessor to the National Institute of Standards and Technology. Now, NIST, the National Archives and Records Administration, NASA and Heery International have teamed to design new state-of-the-art enclosures for the Charters of Freedom.
Deterioration of the glass in the current encasements appears as small surface cracks, crystals and droplets. This deterioration will eventually cause the glass to become opaque. Additionally, contact between the parchment and the glass may cause abrasions. Correcting these problems is currently impossible: the cases are soldered shut and cannot be opened without compromising the seal.
Conservators will be able to be open and reseal the new cases—if it's ever necessary—to examine the documents or modify the interior components. The documents will be mounted so that glass never touches parchment. Ultra-smooth surfaces and the use of atomically larger argon gas rather than helium will prevent leakage. The new design will afford the flexibility to incorporate future conservation techniques as they are developed.
Here are the current specifications for the new encasements:
- Number of encasements - Nine encasements will be built. An "original prototype" (sized for the Bill of Rights), a "final prototype" (sized for the Constitution), and seven final encasements (one based on the size of the Bill of Rights, six based on the size of the Constitution). A manufacturing model (which was unveiled on Mar. 17, 1999) will be used for preliminary testing. The two prototypes will be used as spare encasements.
- Encasement dimensions - There are two sizes: the larger encasement with approximate outside dimensions of 997 millimeters (39-1/4 inches) tall by 962 millimeters (37-7/8 inches) wide will house the Bill of Rights; the smaller encasement with outside dimensions of 997 millimeters (39-1/4 inches) tall by 854 millimeters (33-5/8 inches wide) will house the Declaration of Independence, the four pages of the Constitution (one document per encasement) and the transmittal sheet. Dimensions may change slightly during final design following testing of the manufacturing model in March-April 1999.
- Encasement materials -
Frame - Commercially pure titanium with an appropriate finish selected primarily on aesthetic conditions.
Seal - The seal surface will be machined, diamond turned, plated and post polished after plating.
Base - Monolithic metal (either titanium or an alloy of aluminum). The final determination of the base alloy will be made during the testing scheduled for March-April 1999.
Glass - 9.5 millimeters (3/8 inch) laminated, tempered float glass that may include an anti-reflective coating.
O-rings - One single C-section metal seal with a coating (currently anticipated to be gold).
Platform - The document platform to be high-grade aluminum with holes spaced to provide adequate argon circulation.
Bolts - There will be 74 steel bolts per encasement spaced approximately 50.8 millimeters (2 inches) on center around the perimeter in between the seal surface stiffening ribs. This will provide a seal pressure of 50 newton per millimeter (300 pounds per lineal inch) along the O-ring. The installation time of the bolts is expected to be less than one hour.
Pockets - In an effort to reduce weight, strategic areas (or pockets) of material have been removed from the base, the document platform and the titaniumframe. In the base, the pockets are on the bottom of the base and are approximately 50.8 millimeters (2 inches) square. In the frame, the pockets are in between the bolts and are on the underside of the frame (concealed from view). The pockets in the document platform are approximately 50.8 millimeters (2 inches) on center.
Ports - The ports placed in the base for the required accessories (valves, pressure gauges, sensors, etc) have an inside diameter of 19 millimeters (3/4 inch) spaced approximately 50.8 millimeters (2 inches) on center between the seal surface stiffening ribs centered in the bottom of the encasement. There are currently five ports, but an additional port will be added to the bottom of the encasement (beneath the platform) for passing through of wires for sensors under high-pressure.
Monitoring - A pressure sensor will be provided. Temperature will be monitored outside the encasement. There will be one port provided for possible spectroscopic analysis of the interior gas. A rupture disk will be provided in one of the ports to protect against accidental over- or under-pressurization.
Buffering - There will be at least one layer of pure cellulose paper beneath the document to prevent holes in the document platform from "transmitting" through the document.
Finishes - All metal surfaces (with the exception of the seal surface) are scheduled to be anodized. The anodizing is required primarily for aesthetic reasons but also will minimize handling damage or oxidation. The seal surface is scheduled to be nickel plated and post polished to very tight surface finish tolerances.
- Encasement Environment - Temperature will be 19.4 degrees Celsius (67 degrees Fahrenheit) plus or minus 1.25 degrees Celsius (2 degrees Fahrenheit). The relative humidity of the inert argon gas shall be 40 percent. The display case is to provide 19.4 degrees Celsius (67 degrees Fahrenheit) ambient conditions and a relative humidity of 45 percent plus or minus 5 percent.
For additional PRESS information, please contact the National Archives Public Affairs staff at (301) 837-1700 or by e-mail.
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