Particle accelerator enlisted to uncover mummy’s secrets

On the morning of November 27th, a team of academics carted off the so-called Hibbard mummy from Northwestern University for a 24-hour session with a particle accelerator. The experiment at the Advanced Photon Source at Argonne National Laboratory used high energy X-rays to further probe the material composition of various objects embedded in the mummy without damaging its remains.

This is a far cry from the mummy unwrapping parties that were popular in Victorian England, when Egyptomania gripped the nation in the 19th century. Performed in the name of science and entertainment, those crude experiments tore into mummies, destroying many specimens in the process. But times have changed, and so has the technology.

“Our main motivation is to use the physical sciences to be able to unpack the technology of art,” said Marc Walton, a materials scientist at Northwestern University and a leader of the project. “We’re trying to get into the mind of the artist, if you will, to understand why they’re making certain choices based upon the economics of the materials, their physical structure, and then use that information to be able to rewrite history.”

The Hibbard mummy isn’t some exalted pharoah, wrapped up and buried with untold treasures. It’s the remains of a five-year-old girl who lived in an agricultural community during the late first century A.D. Her home sat in the Faiyum oasis just west of the Nile, at the crossroads of a fading Egyptian and growing Roman empire. Instead of a golden, idealized, three-dimensional face akin to King Tut’s sarcophagus, the Hibbard mummy has a more photorealistic representation of the girl’s face painted onto a wood panel.

Mummy with portrait closeup | Miles O'Brien Productions
The Hibbard mummy. Credit: Northwestern University.

These wood panel paintings, called mummy portraits, represent the largest surviving collection of paintings from antiquity. Preserved by the dry Egyptian climate, thousands of these mummy portraits have been found, but only a small fraction remain intact with their mummy.

Walton is part of a team putting together an exhibition of mummy portraits, but the idea for a high energy examination came after one of the co-curators, Essi Rönkkö, stumbled upon a fully intact mummy, with portrait still attached, at the Garrett-Evangelical Theological Seminary on the Northwestern campus.

“We had a whole intact mummy right here on campus,” Walton said. “The museum community didn’t know it was there!”

As it turns out, a wealthy Chicago family, the Hibbards, had financed Egyptian excavations in the early 20th century and received the mummy as a gift, which they ended up donating to the theological seminary.

In another stroke of luck, the mummy originated from the same region of Egypt as the portraits that the team had already been collecting for the exhibition.

Walton and a colleague from the Classics Department, Taco Terpstra, decided to enlist the help of undergraduate and graduate students in analyzing the mummy’s material makeup with a variety of specialized scans.

Three mummy portraits | Miles O'Brien Productions
Several mummy portraits also discovered in the Faiyum oasis. Credit: Phoebe A. Hearst Museum of Anthropology.

Olivia Dill, a first year art history Ph.D. candidate, is a student who helped conduct a CT scan of the Hibbard mummy to discern how she died. There were no visible injuries, so the researchers think the girl likely succumbed to a disease such as smallpox or malaria.

Mummy gets a CT scan | Miles O'Brien Productions
The Hibbard mummy undergoes a CT scan. Credit: Northwestern University.

But the CT scan revealed other hidden secrets. Wrapped to the little girl’s belly was some kind of small object.

“The resolution on the CT scan is such that we can only barely make out a shape. We think it’s some sort of stone, but we’re not sure,” Dill said, positing it is perhaps a scarab-shaped charm. The same uncertainty surrounds shards of a bowl-shaped object inside the skull, rattling around in the space left behind when the brain was removed in preparation for mummification.

Dill is most excited about examining the two dozen small pins inserted into the wrappings around the feet and head of the mummy. It is unclear “whether they are modern additions possibly due to conservation efforts or if they are contemporary to the rest of the mummy,” Dill said. “We’re hoping that the analysis at the Argonne lab will enable us to identify the material a little more specifically.”

Mummy skull reconstruction | Miles O'Brien Productions
A reconstruction of the bowl-shaped object in the Hibbard mummy’s skull. Credit: Northwestern Memorial Hospital.

The Advanced Photon Source facility of Argonne National Laboratory speeds up electrons along a 3,600 foot circular track to produce high energy x-rays. These beams are used for high-resolution imaging of various materials, from pharmaceutical to microelectronics.

Walton and company opted for this particle accelerator scan because it not only reveal material composition, but characteristics like density and shape — all without physically altering the mummy. Archaeologists have employed the Advanced Photon Source in the past, but never for mummified remains, the team said.

Advanced Photon Source aerial exterior | Miles O'Brien Productions
The Advanced Photon Source. Credit: Argonne National Laboratory.

After working through the night, Stuart Stock, a cell and molecular biologist at the Feinberg School of Medicine at Northwestern University who led the Advanced Photon Source experiment, shared some preliminary findings with Miles O’Brien Productions.

“The shards within the skull do not show any evidence of crystallinity,” Stock said. “I am inclined to think the shards are something noncrystalline like solidified pitch,” meaning the shards came from a thick organic material like tar and not from something fragile like glass, which has a crystal structure.

As for the other objects, Stock said he “can’t say much yet about the inclusions within the wrappings.”

Stock also found fine wires were embedded in the mummy’s teeth, but their composition remains unknown.

Mummy at Advanced Photon Source | Miles O'Brien Productions
Hibbard mummy at the Advanced Photon Source. Credit: Northwestern University.

All this experimentation is helping narrow down the materials used by these cultures. For example, other mummy portraits contain red pigment from lead found in Spain, painted on a type of wood that grows in central Europe–physical proof that trade was flourishing across the vast Roman empire. The students have been analyzing the mummy’s portrait in this context while also running various tests on the mummy itself.

“It’s a person who has been prepared for burial in a very specific and very careful way to ensure a successful afterlife,” Dill said. “Learning that through this project has been very humbling and touching.”

By using these noninvasive scientific instruments, art historians can make sure they are respecting mummified remains while sharing that humbling joy of discovery for generations to come.

To learn more about the Hibbard mummy, and mummy portraits in general, visit the upcoming “Paint the Eyes Softer: Mummy Portraits from Roman Egypt” exhibition at Northwestern University’s Block Museum, done in collaboration with the University of California, Berkeley’s Phoebe A. Hearst Museum of Anthropology. January 13 – April 22, 2018.

A version of this article appeared on the PBS NewsHour website. Banner image credit: Northwestern University.

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