X-rays and the statues eyes

left eyeIn a previous post, we told you that the two wooden heads were going to be X-rayed and CT-scanned, alongside with some other artifacts from the Lab.

In this post we will deal with what we learned about the wooden heads’ eyes from the X-radiographs only.

A lot of our readers will probably know what X-rays are, for they may have experienced them in a hospital. X-rays are also successfully used in Art and Archaeology (for a general overview and some examples, see SCHREINER et al, “X-rays in Art and Archaeology – An overview). The principle of the X-ray is to expose a material to x-ray energy of a particular wavelength. According to the molecular weight of the material, the x-rays will, or won’t, be allowed to go completely through it. The energy that does penetrate passes through to a detector.

In digital radiography, the data is then processed by a computer and, eventually, we obtain a picture where dense (high molecular weight) materials appear white and lighter ones (low molecular weight) are black.

X-ray photograph of E17911

X-ray photograph of E17911 – We can see a lot of termite tunnels and the big hole inside the head, on the right-hand side, and the shining eyes.

E17911, in profile - This picture allows us to see more clearly the structure of the eyes.

E17911, in profile – This picture allows us to see more clearly the structure of the eyes.

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E17910 – Also helpful about the inserting of the eyes.

In these radiographs, we clearly see the structure of the inlaid eyes. In fact, those eyes are quite similar to those studied at the Louvre Museum on Kay’s statue (ZIEGLER, Les statues égyptiennes de l’Ancien Empire, Musée du Louvre, 1997, p.256). This statue is from the Vth Dynasty, not so far in time from our heads.

Eventually, we can conclude that the eyes are made of a metallic sheet soldered in the back, which is flat. It is shell-shaped and the hippo ivory is inserted inside. Then the black pupils (made of obsidian?) are placed in the ivory, maintained inside by an adhesive (resin ? plaster ?).

New Picture (3)

X-ray radiography photograph of Kay’s statue eyes (from ZIEGLER, 1997, p.256).

Structure of Kay's eyes (from ZIEGLER, 1997, p.259); the back of the metallic part is flat and the edges were folded so as to form the eyelids.

Structure of Kay’s eyes (from ZIEGLER, 1997, p.259); the back of the metallic part is flat and the edges were folded so as to form the eyelids.

Structure of Kay's eyes and identification of the materials we have on Adu's eyes (from ZIEGLER, 1997, p.259)

Structure of Kay’s eyes and identification of the materials we have on Adu’s eyes (from ZIEGLER, 1997, p.259)

 

 

 

 

 

 

 

 

 

 

Fortunately, the Penn Museum has some inlaid eyes in storage, allowing us to figure out more clearly what we have on the heads.

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The eye n.E6789B – Limestone and obsidian.

 

Back of the eye n.E12905A - Copper alloy.

Back of the eye n.E12905A – Copper alloy.

 

 

 

 

 

 

 

 

 

 

 

Again, fortunately for us (yes, fortunately!), the Louvre Museum has a very interesting statue, also from the Old Kingdom, with missing eyes. This statue of a nobleman named Tcheti informs us on how the inlaid eyes were inserted into the wood.

Tcheti statue, Louvre Museum n.E11566 - Detail of the missing eyes.

Tcheti statue, Louvre Museum n.E11566 – Detail of the missing eyes.

We can see that a hole was cut in the wood, fitting the eyes’ size. We can suppose that an adhesive was used to prevent the eyes from falling off the statue.

As you can see, a conservation intervention, apart from treating the objects, can also allow us to study them more closely and to know them better.

We will talk about the CT-scan in a next post and, in the meantime, you’re more than welcome to visit us at the Lab or to post a comment below !

 

Looking inside our falcon mummy

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

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 laying on its storage support on the x-ray plate (within a lead-lined room)

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:

falcon xray annotatedHooray! 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.

Right: Lynn Grant and I taped the falcon mummy in his box to the stage inside the CT chamber. Left: another view of the falcon mummy's box secured inside the CT chamber.

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:

falcon cross section annotatedIn 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!

falcon CT 3 views annotatedWe will need to spend time with the images, and consult other specialists, to better understand what the CT scans have revealed.

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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!

 

X-ray excursion

If you stopped by the Artifact Lab this week, you might have noticed that our falcon mummy is no longer on display, and this sign in its place:

falcon signAs indicated on the sign, the falcon has been removed for x-radiography. This mummy has never been x-rayed before, and we’re interested in using this imaging technology to learn how it was made and if there are any falcon remains inside!

Along with the falcon, we’re also going to be x-raying/CT-scanning our (possibly headless) cat mummy, the wooden statue heads, and several other pieces.

We do not have the ability to x-ray and CT-scan objects here in the museum, so we will be taking these selected pieces for a little trip tomorrow. In preparation for their travels, they are securely packed, and ready for this exciting excursion!

The falcon mummy is secured inside its storage support and packed into a larger box for travel.

The falcon mummy is secured inside its storage support and packed into a larger box for travel.

We will update the blog with our findings soon after we return.

 

It’s hard work, but with lots of rewards

As I’ve said before on this blog, one of my favorite parts of my job is meeting our visitors on a daily basis. This kind of interaction is really rewarding for me, and I hope that the feeling is mutual for those who do get a chance to stop by the Artifact Lab during open window sessions. So you can imagine how pleased I was to find this in my mailbox yesterday:

quinn envelope_addressremovedAs soon as I saw this, I knew exactly who it was from. Last week I was visited by three brothers, Sean, Aidan, and Quinn – their Granddad brought them to the museum for a day, and after doing his homework, specifically came up to the Artifact Lab for our 11:15 open window session. They had lots of questions for me, and we talked for awhile about our animal mummies. I explained to them that we don’t need to unwrap these mummies to know what’s inside – x-rays show us that this rather nondescript mummy -

ibis mummy

- is definitely an ibis, indicated by the characteristic long curved beak which is clearly visible in x-radiographs taken from 2 different angles:

The ibis' beak, indicated here with red arrows, is seen in x-radiographs taken from two different angles.

The ibis’ beak is indicated here with red arrows

To illustrate this in the lab, we printed out one of these x-ray images along with a little drawing of an ibis, and we keep it next to the mummy for comparison. As soon as the youngest brother, Quinn, saw the picture, he quipped, “I wish I could color that!”. So I immediately handed it over to him and asked him if, when he was done coloring, he could share a photo of it with me to post on the blog. Well, he sure didn’t waste any time – not only did he send me his drawing (signed and everything):

Quinn drawingbut the brothers also included a very sweet, and beautifully illustrated thank you note.

quinn letter togetherWhat wonderful artists, and very thoughtful boys. Answering questions can be hard! But with visitors like this, it doesn’t feel like hard work-it’s just fun. Thank YOU Aidan, Sean, Quinn, and Granddad Dan for visiting me in the Artifact Lab and being the highlight of my day!