Argon case prescribed for Washington's Magna Carta

The copy of the Magna Carta in the National Archives in Washington, D.C. will have a new, protective case filled with argon. The document is currently housed in a case filled with helium.

Experts feared that the helium gas, which has relatively small atoms, could escape from the current case, leaving the 13th century copy, one of only two outside of England, unprotected. "Argon is used to displace oxygen and any moisture that may be remaining in the encasement area, to preserve the document and minimize degradation," said Mark Luce, an engineer at the National Institute of Standards and Technology.