Last Friday, 7 of us from our conservation department took a group of objects from the museum to the GE Inspection Technologies Customer Solutions Center in Lewistown, PA for x-radiography and CT scanning.
Our group gathered around the CT scanner, being operated by Becky Rudolph, GE’s North American Radiography Sales Manager for Academia
Now, wait just a second, you might be thinking. Doesn’t Penn have its own x-ray and CT scanning equipment? Why did we have to take these objects all the way to Lewistown for this work? Good questions, and we have a good answer. We just received word that in early 2014, construction will begin on our new conservation labs, which will include a digital x-ray suite. We plan to purchase the x-ray unit from GE, so a visit to their facilities was a chance for us to demo the equipment using some of our own artifacts!
The object I was most eager to image was our falcon mummy. X-ray and CT (computed tomography) scanning technology allow us to “virtually unwrap” this mummy, helping us understand how it was made and what is inside (and as visitors to the lab have heard me say, we can’t assume that there are any falcon remains inside-we can only hope!).
The falcon mummy lying on its storage support on the x-ray plate (within a lead-lined room)
The quickest way to get a peek inside the falcon mummy’s wrappings is by taking an x-ray image. Digital x-ray technology is amazing – with a push of a button, 135 kV (kilovolts, measurement of the voltage), 2.0 mA (millamperes, measurement of the current) and 4 seconds later, we saw this:
Hooray! In this first attempt, we could already see that there are bird remains inside. The bright white material concentrated in the center of the mummy wrappings is the skeletal remains. In radiographic images, materials that are denser appear white because they do not allow x-rays to pass through. Materials that are less dense (such as the textile wrappings surrounding the bird bones) appear darker, because the x-rays are penetrating and passing through these materials. We can see in the image above that there are no skeletal remains in the “head” and the “feet” of the falcon mummy – these areas appear to have been sculpted with fabric. The slightly brighter white area near the feet just reflects an overlap of textile in that area.
While we were excited by this image, it immediately prompted more questions. We can see bird bones, but where is the skull? How much of the bird body is present? Are there any clues as to how the body was prepared for mummification? To answer these questions, we turned to the CT scanner.
CT scanning uses x-rays to produce cross-sectional images of an object, which can then be combined to produce three-dimensional views. CT provides a much more detailed look inside objects, and better distinction between different materials.
The CT unit at GE does not look like a medical CT scanner that many people may be familiar with. To scan the falcon, we had to stand the mummy upright in its box, which we then secured to the rotating stage inside the CT chamber with masking tape.
Left: Lynn Grant and I taped the falcon mummy in its box to the stage inside the CT chamber Right: another view of the falcon mummy’s box secured inside the CT chamber
The CT scanning took a bit longer than 4 seconds, but again, produced much more detailed images. Here is what one of the cross-sections looks like:
In this image, the bones are visible as the most radio-opaque materials (so they are bright white). We were also excited to see the feathers, clearly visible as little circles reflecting the cross-section of the feather shafts, which are hollow. The various layers of linen wrapping are also very clear – clear enough to count! But other details are not so immediately clear to us, including the presence of the skull, and exactly how the remains were prepared.
Here is a screen shot from the program we are using to view the CT images, showing 3 different cross-sections, and a basic 3D rendering of a section of the falcon mummy. In this 3D rendering, we can clearly see the falcon’s talons, circled in red!
We will need to spend time with the images, and consult other specialists, to better understand what the CT scans have revealed.
UCLA/Getty graduate intern Alexis North and I puzzle over the CT images of the falcon mummy
We will follow up later with more images and interpretations of the falcon mummy CT scans, plus more about the other objects we were able to examine.
A special thank you to Becky Rudolph and Hank Rowe at GE for spending the day with us, and for their expertise!