Seeing artifacts in a new light: 3D imaging of an Egyptian stela
It is a rare occasion to see a favorite artifact truly in a new light. I got that chance while photographing the ancient Egyptian stela of Wepemnofret before its trip to storage. This mortuary monument to Prince Wepie, as we like to call him, is one of the star pieces of the Hearst Museum’s Egyptian collection. The decoration shows him seated before a table of bread, with lists of his worldly titles and desired offerings for his eternal afterlife. The limestone is carved with delicate, low relief that is overshadowed by the uniquely preserved brightly painted details. The combination of carved and painted decoration is a hallmark of Egyptian art, and works together to make the Stela of Wepemnofret a masterpiece of Old Kingdom art (2575-2134 BCE). As the stela was prepared for movement, I was able to use an advanced 3D imaging technique to bring out the surface details of the piece and get a new look at Wepemnofret.
Wepemnofret with strong enhancement, RTI image (PAHMA)
The 3D imaging technique of Reflectance Transformation Imaging (RTI) was invented at Hewlett Packard, and our project used the software and workflow developed by San Francisco based Cultural Heritage Imaging (culturalheritageimaging.org). Several of our museum staff members have gone through their excellent training course and learned about this imaging technique. RTI images take digital photographs into the third dimension by adding another layer of information to the file. Each pixel in a normal image file contains a color value, but in a RTI there is also a vector value—the angle or slope of surface the object at that given point. The viewing program can then calculate what the object should look like under different lighting angles, and better yet, can enhance surface details that cannot be seen under real-world viewing conditions.
Wepemnofret under real lighting condition, with RTI capture set up (PAHMA)
To capture the RTI, I placed a reflective black sphere near to, but not touching, the stela. I made mine from a billiard ball coated in several layers of black nail polish, well cured for a week in a ventilated area, and drilled with a screw thread for attachment to a tripod. As seen below, my assistant held a length of string as I positioned the light source at about 50 different angles around the stela. Each image with each different angle was compiled by the CHI open-source software, with the highlight on the reflective sphere telling the program the angle of the light source. Finally, with that information the CHI viewing software gave us an interactive model of the decorated surface (see video).
Photographer Elizabeth Minor and assistant Kierstin Sakai during RTI capture, with raking light angle (PAHMA)
Every small detail in the carving pops out with the enhanced surface, and you can see individual feathers, whiskers, and even twists of rope in the hieroglyphs. The miniature lines and textures in the painting add life to each symbol. Wepemnofret himself has carefully placed folds of muscles and skin in his face, arms, and legs. You can also clearly see where the painter did not follow the outlines of the relief, or fixed spelling errors, as previously noted by Manuelian (2003). Despite the high skills of the relief carver and painter, their coordination was not as careful as possible.
Hieroglyphs in title of Wepemnofret with very strong enhancement, RTI image (PAHMA)
In comparison, the Stela of Kanofer is more damaged and has no remaining paint. The RTI helps bring out the carving of the bright white limestone, and you can see that Kanofer’s relief is not quite as detailed as Wepemnofret’s. It’s a stroke of archaeological luck that the paint is preserved on the Stela of Wepemnofret, and with this imaging technique we can further appreciate the skills of the artists who created it.
Wepemnofret with low enhancement, RTI image (PAHMA)
Original field photo of Wepemnofret, 1905 (B11762, Museum of Fine Arts, Boston)
Field photo of stela in place, with covering block first removed (B11057, Museum of Fine Arts, Boston)