Dr. Douglas Robertson swears that one of the best vantage points for observing a 5,300-year-old Egyptian mummy mask is in his laboratory at UPMC Montefiore.

	University of Pittsburgh Medical Center Computer model of an Egyptian mummy's mask shows the bare, geometrical model on the left, and, on the right, a texture map version in which photographs of the mask have been combined with the 3-D model. Click photo for larger image.

Make no mistake: The funerary mask of what may have been a noblewoman from the court of Ramses the Great is physically on display 550 miles away at the St. Louis Art Museum. But a full-color, three-dimensional model of the mask resides in Robertson's computer.

And only the computer model can be turned or flipped for viewing at any angle.

That's not something a museum visitor could or should ever attempt with the real thing. "Even the art curators don't touch it," said Robertson, a radiologist who directs the musculoskeletal imaging and biomechanics laboratory at the University of Pittsburgh.

A 3-D computer model, by contrast, is just a bunch of numbers, so it can't break, crack or smudge. But it can be copied, altered or subdivided for analysis with ease.

Computer modeling thus is becoming an important new tool for museum curators.

The model of the Egyptian mummy mask ---- the first use of CT scanning and 3-D modeling of an antiquity with both an outer and an inner surface ---- has been used to understand the handiwork necessary to produce it, to identify previously repaired areas and to plan reconstruction of a damaged portion.

Robertson contends the model eventually could be part of the museum exhibit, or used to allow people to study it from remote locations.

Some museums already have incorporated computer models into their displays, such as the "Ancient Bronzes of the Asian Grasslands" exhibit that opened this fall at the Carnegie Museum of Natural History. Carnegie Mellon University computer scientist Yang Cai and his students worked with archaeologists and artists to render the face of a Botai horse herder based on a 5,500-year-old skull unearthed in Kazakhstan.

Cai's students also used computer modeling to produce a 3-D panorama of Krasnyi Yar, a Botai village that today is nothing but a series of depressions where its buildings once stood on the northern Kazakhstan plain.

"This kind of computer reconstruction helps the archaeologist envision what these villages looked like," said Sandra Olsen, curator of the anthropology section, whose research focuses on the Botai culture and the domestication of horses.

By understanding the size, spacing and appearance of the houses and corrals of the village, she added, "I think it's easier to visualize what their daily lives were like."

Modeling the mask

"It's a new era," said Robertson, who became involved in imaging the mummy mask several years ago while on the faculty of Washington University in St. Louis.

	Yang Cai, Ashley Brickman, Liya Zheng and Jeffrey Dolin Horn, CMU Part of a three-dimensional computer panorama of the ancient Kazakh village of Krasnyi Yar. Click photo for larger image.

The art museum has a long relationship with Washington University's radiology department, which scans many of the museum's artifacts. The mummy mask was studied using a CT scanner, which produced a series of horizontal slices through the mask at 1 millimeter intervals.

The mask, from Egypt's 19th Dynasty, is made of linen and plaster, with a gold foil skin, tar-like bitumen hair, glass inlays and wooden amulets. It was featured in the St. Louis museum's traveling exhibit, "Masks," and is now on display in the museum.

It wasn't until Robertson joined the University of Pittsburgh School of Medicine a couple years ago that he began to use those earlier CT scans to build a 3-D computer model of the mask.

In his lab, Robertson and his students spend most of their time producing 3-D models of bones, which are used for such applications as designing new artificial hip joints and other implants.

"In a way, the mask is just another body part to us," he said. Like body parts, the mask isn't designed using easy geometric shapes such as cones or cylinders. "A lot of engineering software isn't designed for natural shapes," he noted, so special software and techniques are often necessary.

At its simplest, the 3-D model describes the contours of the mask as a network of triangles. But Robertson also wanted to overlay the model with photographic images of the exterior, a process called texture mapping.

The mask was photographed at 45 degree intervals. To combine these two-dimensional images with the 3-D model, the model's triangles had to be flattened out into two dimensions.

This flattened model was highly distorted, but Robertson's engineering graduate student, Gulshan Sharma, and one of Cai's students, Jason Fung, were able to painstakingly match the photographic images to the model, beginning first with identifiable landmarks such as the eyes and mouth.

The result revealed some craftsmanship that had previously gone unnoticed, Robertson said. The CT scans revealed areas with differing linen quality, suggesting repairs had been made. Some details that appeared to have been simply painted on the mask were shown in the texture-mapped model to actually have been carved first, then painted.

"If there was a difficult way to [make] it, they did it," said Robertson, who presented a paper on the mask modeling last month at the Radiological Society of North America meeting in Chicago.

The top left side of the mask has been damaged, as if it fell or was dropped, and one hope was to use the 3-D modeling to guide the reconstruction of the mask by the museum's conservator, said Sidney Goldstein, curator for ancient and Islamic art.

The numerical model made it easy, using rapid prototyping techniques, to produce an exact silicone plastic copy of the mask. The plan was to use the copy to fashion "a kind of an implant" for the missing area, which could then be transferred to the mask itself, Goldstein said. But those plans were placed on hold when the objects conservator left the museum.

"It's such a spectacular object ---- everyone wants to see it," Goldstein said, so the museum hasn't been in a hurry to begin a long, laborious restoration that would take it off of display.

Adding a face to a skull

Cai, director of the Visual Intelligence Studio at Carnegie Mellon, had sought out Olsen a couple of years ago because he was interested in getting his class of art and computer science students involved in an archaeological project.

Sandra Olsen and Mark A. Klingler, Carnegie Museum of Natural History, Amanda Amodio, Lindsey Cortese, Yang Cai, Carnegie Mellon University Facial reconstruction of Botai man from approximately 5,500 years ago. This composite shows the actual skull specimen, a surface reconstruction of the head done by computer modeling from the skull measurements and an artist's interpretation of the face. Click photo for larger image.

Using software from a Canadian company, Reflex 3-D Systems, he and his students took a 5,500-year-old skull Olsen had recovered from Kazakhstan and digitally added muscle, fat and skin to reconstruct the horseman's face.

"It came out looking incredibly like a modern Kazakh person, the nose in particular," Olsen said. "We really didn't know if he would come out looking more Indo-European or Chinese. But if you saw [the digitally reconstructed man] on the street, you'd swear he was a Kazakh."

The exhibit shows the skull and the digital reconstruction, as well as a more elaborate rendering by museum artist Mark A. Klingler, who based it on features from four modern Kazakh men.

Using photos and geomagnetic maps showing the size and location of buildings in the ancient village of Krasnyi Yar, Cai's students produced a panorama showing buildings with earthen walls and grass roofs similar to those still used in Kazakhstan.

Cai said they also produced a DVD version ---- not part of the museum exhibit ---- that allows the user to look around the village, as well as look at it from above.

"The computer pulls everything together," Cai said, "and we discover more than is possible with just a [two-dimensional] painting."