X-Rays Are Revealing the Mysterious Writings in Mummy Coffins

October 27, 2016

It’s a sleepy summer Friday at Lawrence Berkeley Lab’s Advanced Light Source. The particle accelerator operates at a constant, gentle hum—quieter than you’d expect for a synchrotron that whirls electrons to just short of the speed of light. Most of the 40 experimental beam lines lie empty.

But one X-ray beam is a hub of activity—an arts and crafts session, by the look of it. The researchers crowding the narrow galley huddle over scraps of papyrus paper, streaking them with metallic paint markers, pencils, and pens. They roll the samples up onto dowels, or crumple them up, or fasten them to each other in layers. The idea? Devise creative ways to hide the ink out of sight, and see if X-rays can uncover it.

It’s a space-age solution to an ancient problem. For more than a century, archaeologists have dismantled mummy coffins, also known as cartonnage, in a hunt for literary treasure. In ancient Egypt, undertakers entombed the departed middle-class in sheets of papyrus thrown out by local scribes, hiding the recycled wrapping with a layer of paint and plaster, or gesso. To uncover the text—everything from bills of sale to the rare castoff of Greek literature—collectors use invasive methods, including massaging intact coverings in a sink full of Palmolive suds.

The trouble is, it’s impossible to know if you’re searching for Sophocles or a shopping list before dissolving an artifact.

Mike Toth hopes to take the guesswork out of that hunt. A private imaging expert specializing in cultural heritage, he’s partnering with archaeologists, physicists, and engineers from Berkeley, Duke, UCL, and Stanford to develop imaging tools that can read the text buried in these objects without pulling them apart.

Reading those hidden layers of papyrus is like rummaging through an old, forgotten filing cabinet. “These contain the lives and challenges of ordinary people,” explains Joshua Sosin, a professor of classical studies at Duke—particularly the lives of women, who are largely left out of the historical record. “We have hate mail, the strange diary ramblings of a hypochondriac, contracts and bills of sale.” And the occasional relic: Christian scripture or a long-lost literary treasure.

Old and New

Most often, an archaeologist with a lead on some intriguing ink won’t head straight to the particle accelerator. Toth jets around the world with equipment for multi-spectral imaging, which floods an artifact with light at a series of increasing wavelengths—purple to red to infrared—in a kind of slow-motion psychedelic light show. Each wavelength glances away differently depending on the material it encounters, yielding a series of images that define areas invisible to the eye. He’s used the method to pick out mathematical proofs by Archimedes smeared over in the Middle Ages, and a fingerprint that clasped an early draft of the Gettysburg Address.

For mummy cartonnage, multi-spectral radiation is a good baseline. But things get complicated fast. Unlike the parchment of the Gettysburg Address, the papyrus layers are haphazard, fused and interlaced with plaster into what Toth calls a “papyrus mâché.” Add to that the folds and wrinkles of age and layers of mold and grime, and you’ve soon got a puzzle worthy of a particle physicist.

That’s where Stanford physicist Uwe Bergmann comes in. He was studying photosynthesis in spinach, which involves detecting trace metals, when he stumbled upon an article about Toth’s work on Archimedes. The secret to revealing the hidden text, he reasoned, could lie in the composition of the ink, which could contain heavy elements like bromine or iron. Fire X-rays at them and they’ll emit unique fluorescent signatures of their own, indicating the presence of ink within the mess of the papyrus mâché. “If we can study these metals at very low concentrations,” Bergmann says, “why wouldn’t we use that same method to image and read the text?”

That’s true of many of the inks used on papyrus as well—but not all of them. Just as you could reach for a number two pencil instead of a gel pen to scribble down a note, some ancients inks are carbon-based, and thus barely discernible from the papyrus.

It’s problem cases like those that brought Bergmann’s team across the San Francisco Bay to the particle accelerator at Lawrence Berkeley. Ancient papyri have been scanned here before, but today scientists are working with test papyrus to figure out which techniques and energy levels work best. Typically, those levels are lower than you’d think—as low as 6,000 electron-volts, far less than your last dental X-ray. But the images produced at Berkeley hone in at 3-micron resolution—less than the diameter of a human red blood cell. With phase contrast imaging at that resolution, you can ideally see the faint outline of the text on the papyrus, and even the shallow impressions made as writing implements etched the fibers.

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