How to read a dirty papyrus.

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April 18 2005 11:48 PM

How To Read a Dirty Papyrus

First, call NASA.

Explainer: How They Read Those Ruined Papyri
Ol' dirty writings

According to an article in The Independent, researchers at Oxford University have deciphered several ancient manuscripts within the past few days, and may have found previously undiscovered works by Sophocles and others. They're examining the original documents with a technology called "multispectral imaging," which allows them to distinguish writing on strips of dirty, moldy, stained, or otherwise illegible papyrus. What is multi-spectral imaging?

Daniel Engber Daniel Engber

Daniel Engber is a columnist for Slate

It's a technique that was developed in the early 1990s to decode parts of the Dead Sea Scrolls. Certain fragments of the scrolls were so degraded that the ink was impossible to see with the naked eye. Then Gregory Bearman, an engineer at NASA's Jet Propulsion Laboratory, came up with a way to read the ancient texts by adapting an imaging technology already used by satellites.

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Multispectral imaging takes advantage of the fact that digital cameras equipped with special filters can record fine distinctions that are invisible to the naked eye. Our eyes perceive different wavelengths of light as color, but this sense isn't very refined. When we look at a degraded or dirty manuscript, the ink might seem indistinguishable from the paper it's written on—even if it appears different from the paper at wavelengths we can't see. But materials can sometimes be distinguished from one another by the way in which they reflect light at invisible wavelengths: A certain kind of ink, for example, might have one spectral signature while a piece of papyrus would have another. If you take a picture of the manuscript with just the right filter, you'll be able to make out the ink on the papyrus and read what it says.

When researchers use multispectral imaging, they take many pictures of the same object or scene; for each shot, they use a different filter that's finely tuned to capture only certain wavelengths of light. Given enough of these images, the researchers can find the best slice of spectrum for distinguishing ink from paper. Charred papyrus buried by Mount Vesuvius turned out to be legible using multispectral imaging. The technique didn't work quite as well for the burnt papyri at Petra, perhaps because they were written in a different kind of ink.

Before multispectral imaging, classicists sometimes tried to uncover hidden text using infrared photography. If a piece of parchment or papyrus appeared blackened to the naked eye—because it had been burned, or irrevocably dirtied—researchers would take a picture, with infrared film, of wavelengths of light we don't normally see. But these images were not very precise: A wide range of wavelengths showed up, and more subtle differences between the ink and paper were not always discernable.

Explainer thanks Traianos Gagos of the University of Michigan and Gregory Bearman of the Jet Propulsion Laboratory.

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