Mad About Science: Preserving and restoring documents

By Brenden Bobby
Reader Columnist

Anyone who has watched the Nicholas Cage adventure epic, National Treasure, has witnessed how not to preserve a historical document.

In the film, Cage’s character steals the Declaration of Independence from the National Archives in Washington, D.C. to prevent a treasure-hunting adversary from doing the same. In the process, he manages to repeatedly roll and unroll the document, as well as coating it in acidic lemon juice and even blasting it with a hair dryer to coax out hidden messages scrawled in invisible ink on the back of the map.

It’s worth noting that there aren’t any hidden messages scrawled in invisible ink on the back of the Declaration of Independence. No matter what Aunt Karen may have shared with you on Facebook, it’s just not true.

The preservation of historical documents is a tradition as old as our ability to write down our thoughts. The libraries of antiquity, such as the colossal Library of Alexandria, had scholars who dedicated their lives to the preservation and replication of important documents. Skilled as they were, the scholars of the Library of Alexandria could not preserve their documents through two catastrophic fires. Thanks, Caesar…

The best method for preserving historical documents has always been to replicate them. After all, the knowledge contained within the document is far more valuable than the paper itself. In some respects, this is a philosophy that still rings true today, as digitization has become the primary form of document preservation. The speed and ease of digitization has allowed us to preserve all sorts of documents, and not just the most important ones like treaties and constitutions around the world. You can even access newspapers from the late 1800s through the digital library at ebonnerlibrary.org.

You’re probably more interested in how organizations like the National Archives and the Smithsonian preserve physical documents, as opposed to their digital counterparts. An immense amount of science and technology go into keeping these documents intact for future generations, though much of it is simpler than you might expect.

Document preservation is all about keeping things consistent and balanced in a way that all pieces of the document are the least likely to degrade. The greatest threats to paper are all too small for our eyes to see. Fungal spores are eager to feast on the organic compounds contained in paper, which would allow the mold to quickly reproduce and escalate the destruction of the document. Additionally, the presence of bacteria and fungi can draw insects, which will draw even larger pests like mice and rats that can destroy a document in mere seconds.

Temperature and humidity are balanced to keep the structural integrity of the documents from altering. As temperature rises, the molecules that constitute a larger structure will vibrate and cause the structure to expand. As the temperature cools, the reverse will happen and the item will shrink. Repeated expansion and contraction will wreak havoc on the structure of a brittle document. Additionally, increased humidity will both damage the item’s structure as well as foster the growth of mold, while too little will dry out the parchment and cause it to fall apart.

The Declaration of Independence is stored in an enclosure filled with argon gas to keep conditions at a consistent 67 degrees Fahrenheit and 40% humidity.

Finally, one of the greatest threats to aging paper is the very thing we need in order to see and appreciate it: light. When light strikes matter, it transfers some of its energy to create heat. This is particularly true of ultraviolet light, as you may notice when you leave an object laying out in the sun for extended periods of time, it will be warmer than something in the shadows and will eventually become very pale. The energy introduced to the surface of the item by light causes tiny chemical reactions to occur. Generally, these reactions are polymer chains breaking down. Certain polymer chain configurations present in pigments used in inks absorb certain wavelengths of light in the visible spectrum – so long as the polymer chains are intact. Once the light starts to break down these polymer chains, items will stop reflecting those wavelengths and just bounce back ambient white light. This is great for a crisp, white piece of copy paper, but devastating for ancient documents.

The last bit of information I have might surprise you. You’d think that anyone handling these documents would be wearing gloves, right? Our hands are filthy conduits for microbes and grime that would then transfer onto the documents and do irreparable harm. It only makes sense to wear gloves.

It turns out that’s not the case. Archivists thoroughly clean their hands and handle documents barehanded. Gloves block our tactile senses and make it far more likely to damage the document accidentally in the process. White cotton gloves you see scientists and archivists using in the movies are some of the worst things to wear when handling ancient artifacts. The nature of woven textiles leaves tiny gaps that catch on surfaces and make for prime real estate for bacteria, mold spores and grime to hide away. Even nitrile and latex gloves can trigger unwanted chemical reactions that we can’t see until the damage has been done.

Stay curious, 7B.

This topic was suggested by Lyndsie Kiebert-Carey. Thanks, Lyndsie!