Conservators Suzanne Davis (left) and Janelle Batkin-Hall (right) performing RTI imaging at El-Kurru. (Photo: Walter de Winter)

by Janelle Batkin-Hall, Graduate Intern of Conservation

Fulfilling a year-long internship at the Kelsey Museum of Archaeology has provided me with some pretty amazing experiences.  Not only have I treated the museum’s archaeological objects excavated from Egypt, but this winter I performed on-site conservation treatments in Africa.  The museum’s head of conservation, Suzanne Davis, and I recently returned from an amazing 6-week trip to the El-Kurru Settlement Project in north Sudan where we performed reflective transformation imaging (RTI) to 200+ ancient geometric and figural graffiti located on the sandstone columns and walls of a Napatan period funerary temple (about 800 - 600 BC).  It is believed that visitors to the temple during the Meroitic period (about 300BC - 400AD) would inscribe the columns and well faces as part of a devotional religious practice.

As a newbie to the challenges of working on-site in the desert (extreme heat, UV exposure, and dust storms, just to name a few), I relied on the guidance of El-Kurru veteran, Suzanne, to show me the ropes, as it was her third consecutive year working at the site.  This season, Suzanne and the project director, Kelsey research scientist Geoff Emberling, initially wanted to implement a treatment plan for consolidating the fragile sandstone columns of the temple, which Geoff finished excavating two years ago.  Continued excavations along a section of the early Christian-era city wall were also to be undertaken.  This is where, in past seasons, a plethora of ceramic sherds were unearthed.  Because, what would an excavation be without masses of pottery?  Therefore, the reconstruction of ceramics would also play a large role in the overall conservation plan.  But, as luck would have it, the challenge of working in a country under U.S. sanctions reared its ugly head.

For months prior to our departure date, Suzanne was diligently trying to find companies in Europe and North Africa that would not only sell us the alkoxysilane stone consolidant, but ship it to Sudan as well.  Despite the fact that the product is not subject to trade restrictions, companies would not ship the product or wanted an exorbitant amount of money to do so.  Therefore, we decided to shift our focus from treatment to intensive documentation.

In total, we conducted three types of graffiti documentation: a criterion anchored rating (CAR) survey to document the condition of the graffiti; inventory photography of each graffito under ambient lighting conditions, one photograph with a centimeter scale and QP gray card (for color correction), and one without; and reflectance transformation imaging (RTI) of each graffito.  Inventory photos and database records were also created for modern graffiti and inscriptions to assist in monitoring the small, but significant amount of defacement that occurs each year.

We chose the RTI imaging technique because it can be used to examine illegible or extremely worn surfaces which have lost detail. For the Kurru graffiti, which are subject to ongoing disintegration and loss, it is an excellent technique for documentation because each pixel records surface texture in addition to color.  The Kurru graffiti were documented using highlight image capture, where the camera remains fixed.  Approximately 48 digital images are taken of the object (or in this case, graffito), using a portable flash at intervals which create a dome of light over the surface. Two reflective black spheres are also fixed within the image frame, and the reflection of the flash on these spheres allows the processing software to calculate the light direction for each image. The resulting images are combined with software, resulting in a single file. In this file, the viewer can move light across the surface in order to examine it from any angle. 

I was familiar with Cultural Heritage Imaging (CHI) from a hands-on RTI workshop I attended at Buffalo State College, where I am a conservation student.  Using the techniques I learned at this workshop and the basic capture and processing recommendations made by CHI, I made a number of small but important changes to the basic CHI protocol that would adapt to our field capture conditions.  These included using a light weight and portable point-and-shoot camera with a two-second delay (no remote), and a special Ethafoam Volara and Velcro belt to suspend the spheres on either curved or vertical surfaces.

After documenting a few graffiti, I realized we needed to adjust our image capture protocol slightly to minimize ANY camera movement.  Since the floor/ground of the temple courtyard is comprised of loose sand over sandstone bedrock, we found that some images were blurry in the upper right hand corner; the area representing the first twelve images taken.  After inspecting the captured jpeg photos we discovered slight camera movement that was most likely due to the tripod on the unstable sand.  To remedy this, five “blank” photos were taken to settle the tripod so that it did not move during the actual photo capture sequence.  To capture the larger size graffiti on a curved surface, the first photo taken for each “rib” was adjusted from CHI’s recommended 15 degree inclination to approximately 7-10 degrees.  Then, CHI’s recommended four photos between 15 and 60 degree inclinations were taken.  We also discovered that direct sunlight cast onto the flash unit’s infrared (IR) sensor would cause it not to fire, as the sunlight would disrupt the IR signal between the transmitter and flash. Therefore, the flash IR sensor was shaded, but not blocked.

For me, this was a great experience because I was able to use a technique I recently learned in graduate school. Being able to apply it onsite and share the results with our colleagues was very rewarding.

 

Screen capture of bull graffiti using CHI’s RTIViewer software.