How Imaging Science Reveals Historical Secrets

By: Hannah Pell

In the 2004 movie National Treasure, the main character Ben Gates — a historian, cryptographer, and treasure hunter played by Nicholas Cage — is determined to solve the generational mystery passed down to him from his grandfather. The only clue that Ben has is: The secret lies with Charlotte. Based on this, he leads his team to a lost Arctic ship named Charlotte, in which he finds another clue that leads him straight to the Declaration of Independence.

“I’m going to steal the Declaration of Independence,” he declares.

Spoiler alert if you haven’t seen the movie: he does. A treasure map is supposedly hidden somewhere on the Declaration. Once they’ve successfully stolen it, Gates and his team turn the document over very carefully and — with the help of lemon juice and hair dryers — an Ottendorf cipher written in invisible ink gradually begins to appear. A map!

The long lost historical secret is finally revealed.

Unfortunately, movies are just movies. If a real historian was certain that an old document contained hidden information, maybe if the document was a palimpsest — a manuscript from which previous text had been scraped or washed off — how would they go about revealing what’s hidden? Thankfully, imaging techniques and conservation science can help. 

Hyperspectral imaging on a section of a rough draft of the Declaration of Independence reveals Thomas Jefferson originally used the word “subjects” instead of “citizens.” Image Credit: The Getty Conservation Institute / Library of Congress.

Conservation science is the study of the conservation of art, architecture, and other cultural works through scientific inquiry. This interdisciplinary field brings together chemists, physicists, biologists, engineers, historians and anthropologists alike who work towards a common goal — to understand, study, and preserve artistic materials. Optics is the key to doing so.

There are many different imaging techniques used for uncovering hidden aspects of old texts or paintings. In 2015, a team of scientists used X-ray fluorescence spectroscopy and synchrotron radiation in combination to study 15th to 17th century administrative Italian documents. Multispectral imaging revealed two long-hidden treatises by the famous Greek mathematician Archimedes — The Method and Stomachion — that had been erased and overwritten as a prayer book called Johannes Myronas in 1229 AD. More recently, undergraduate students at the Rochester Institute of Technology discovered that a 15th century document was actually a palimpset when they captured previously unidentified text using an imaging system that they developed

In addition to ancient texts, conservation scientists have uncovered secrets in paintings, too. Optical physicist John Delaney, senior imaging scientist at the US National Gallery of Art, analyzed Pablo Picasso’s Mother and Child by the Sea (1902) using hyperspectral imaging and found an entirely different picture underneath. 


Hyperspectral imaging is particularly useful because it is non-invasive. Paints and pigments become transparent when bombarded with radiation at large wavelengths, which can often provide useful information to accurately date a historical work of art. Therefore, scientists also use these same techniques to determine whether a piece of art is real or a counterfeit fake.

Several years ago, conservation scientist Jamie Martin discovered that a painting attributed to Jackson Pollock was, in fact, a fake. Using a Raman microscope and stereomicroscope, Martin identified Red 170 in the artwork, a pigment that wasn’t available until long after Pollock’s death. It turned out that this painting was one of 40 forgeries created by the same artist that amounted to a total of $80 million — the biggest art scam in American history.

“It’s my job to use technology and research to tell the story of a work of art,” Martin told Wired in 2016. “As a scientist, I feel a responsibility to preserve art history so that future generations have an accurate, rich understanding of who these artists were and what they created.”

Sophisticated imaging techniques and conservation science are important not only for studying historical documents, but also for preserving them. Organizations like The Getty Conservation Institute specialize in preserving old materials and artwork. “Imaging throws open new portals to what we could not visualize or even imagine before, helping us better understand, appreciate, and preserve our cultural heritage,” wrote Fenella G. France, chief of the Preservation Research and Testing Division of the Library of Congress.

Imaging science reveals hidden histories; it creates a window into the past we may haven’t looked through before. Improvements in optical technology and imaging methods allow us to paint more detailed and complex pictures of the past than we could have before. Maybe next time someone wants to check the back of the Declaration of Independence for a hidden treasure map, they’ll call a conservation scientist instead.

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