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In the late 1700s, three of the world's most important documents were written here in the

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United States.

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Now called the Charters of Freedom, the Declaration of Independence, the Constitution, and the

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Bill of Rights were conceived and written by early Americans who believed that tyrannical

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rule and oppression should be replaced by individual liberties and freedom.

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Until the mid-20th century, these documents were proudly displayed for the general public,

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but the years of inadequate preservation left them a bit faded and brittle.

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This all changed in 1951 when the documents were placed in specially adapted encasements

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which were designed to slow down the deterioration process.

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These glass encasements were filled with inner helium, which would protect the documents

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from the harmful chemically corrosive effects of air, keeping them safe for generations

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to come.

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But in the late 1990s, conservators began noticing that the documents were, in fact,

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still showing signs of deterioration.

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Mysterious small white spots were appearing inside the encasements and on the documents.

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To help determine the cause of the deterioration and how to fix the problem, the National Archives

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asked researchers at NASA to perform a series of tests on the atmosphere inside the encasements.

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I spoke with Dr. Joel Levine at NASA Langley Research Center to find out more.

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In 1951, the National Bureau of Standards, which is now NIST, the National Institute

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of Standards and Technology, was asked by the National Archives to preserve these very

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important documents, the Declaration of Independence, the U.S. Constitution, and the Bill of Rights.

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It became apparent several years prior to 1998 that some mysterious white spots appeared

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in all encasements, and over time, over several years, they increased in number.

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The National Archives conservators wanted to know if we had technology that could determine

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the chemical composition of the encasements noninvasively.

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Noninvasively means without extracting air.

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We didn't want to touch the air.

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We didn't want to touch the encasement.

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We wanted to come up with some technique that could tell us the answer without disturbing

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the contents of the encasement, both the documents and the atmosphere.

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After considerable discussion, we decided we should use a technique called laser spectroscopy.

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What the laser did is provide energy at the very wavelength that water vapor absorbs,

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and as we looked at the absorption, we could determine what the background gas was.

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We're interested in not the document, but the atmosphere in the encasement that's protecting

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the document.

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What we found is that the gas that was sealed 50 years ago was still there.

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When the laser studies were done, NASA researchers conclusively determined that helium in the

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encasements had not leaked out.

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This determination only increased concerns over the origin of the mysterious white spots.

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Most conservators believed that chemically corrosive air had leaked into the encasements,

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causing the damage.

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With this belief dispelled, the puzzle only intensified.

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So in some instance, we actually went back to step one because we still had the problem.

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The problem is what is responsible for these white spots.

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We eliminated air as a corrosive agent, and the next thing the National Archives asked

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us is could we tell them noninvasively how much water vapor was in the encasement.

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Because the documents were written on sheepskin, which requires a small amount of water vapor

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for stability, the relative humidity inside the encasements was originally set between

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25 and 35 percent.

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To determine if the humidity levels had changed, the NASA researchers needed to measure the

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relative humidity inside the sealed encasement.

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The first technique considered involved placing the encasements in a freezer to cause the

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condensation of gaseous water vapor to liquid water droplets.

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This idea was rejected due to the distinct possibility that the documents inside could

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be damaged by the condensed water.

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It was later decided that the humidity could be checked by using a very inexpensive device

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called a thermal electro-cooler.

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This device would sample only a small area of the encasements, keeping the documents

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inside safe.

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I called up the archives and I said we just have to freeze a small part of it at the edge

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where there is no document, no ink, and we can solve your problem.

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When the humidity levels were checked, it was found that the levels inside the encasement

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were 60 to 65 percent, twice the expected relative humidity.

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This is because when the documents were originally sealed in 1951, the relative humidity in Washington,

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D.C. was very high.

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The backing paper that the documents were laid upon had actually soaked up water vapor

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like a sponge.

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Once the documents were encased, the water vapor inside the backing paper could not escape,

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so it remained in the encasement's atmosphere, causing the humidity to rise.

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The white spots were basic or alkaline chemicals that were pulled out of the glass because

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of the presence of high levels of water vapor.

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And now, when the National Archives opens with its new encasements, we are all sure

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that the documents will be stable for many centuries, and in some small part, NASA scientists

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and NASA technology help preserve these documents for many generations to come.