APPEAR Project – Portable X-Ray Fluorescence on the Fayum Mummy Portraits

Hi! This is Eve Mayberger with another update on the Ancient Panel Painting: Examination, Research, and Research (APPEAR) project (see earlier posts here and here). I recently investigated the pigments used on the three Fayum mummy portraits with the portable x-ray fluorescence (pXRF). While the pXRF results for all three portraits are interesting, I am going to briefly discuss the findings for the Portrait of a Woman (E16214).

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APPEAR Project, Portrait of a Woman (E16214); Annotation of pXRF test locations

One of the major advantages of pXRF is that it is a non-destructive technique that uses x-rays to identify specific elements. The technique can help to characterize pigments and metal alloy components. It is important to remember that pXRF is a surface technique and will only detect elements present on the surface. I decided to analyze the seven different colors used on the mummy portrait to determine if there are any elemental differences.

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Collecting data with the Brucker pXRF

All the test locations recorded prominent peaks for calcium (Ca), iron (Fe), and lead (Pb). Although there is some variation in peak heights across the test spots, it is important to remember that pXRF is a qualitative not a quantitative technique. See below for a representative spectrum for six out of the seven analyzed locations.

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APPEAR Project, Portrait of a Woman (E16214); Spectrum for sample #2 – forehead; Peaks detected for Ca, Fe, and Pb

The green used to paint the gemstones on the woman’s necklace has an additional peak for copper (Cu). This is not surprising as many greens have a copper component. In ancient Egypt, the greens were generally made with malachite or green earths, or from a mixture of blue and yellow pigments. While malachite is a copper-based compound, more analysis is needed to confidently identify the green pigment used for the gemstones.

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APPEAR Project, Portrait of a Woman (E16214); Spectrum for sample #5 – gemstone on necklace; Peaks detected for Ca, Fe, Pb, and Cu

It should be noted that not all pigments can be identified with pXRF alone. Some organic pigments, such as madder, cannot be detected with pXRF. In addition to using analytical instrumentation, it is also important to know what colorants are expected on specific artifacts to help limit the number of possible pigments.

Be sure to visit the blog in the upcoming weeks to read more about the APPEAR project!

Eve Mayberger, Curriculum Intern

APPEAR Project – Multispectral Imaging on the Fayum Mummy Portraits

Hi! This is Eve Mayberger with an update on the Ancient Panel Painting: Examination, Research and Research (APPEAR) project (see earlier post here). I am happy to report that I have completed multispectral imaging (MSI) for the three Fayum mummy portraits. The In the Artifact Lab blog has talked about MSI in several previous posts here and here. MSI is a helpful technique that uses specific frequencies across the electromagnetic spectrum to differentiate and sometimes identify materials.

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APPEAR Project, Portrait of a Young Man (E16213)                                                                          Visible (VIS) image. Captured with a Nikon D5200, modified by replacing the hot mirror filter with a glass custom full spectrum filter, B+W UV-IR cut filter (#486 MRC), and incandescent photo light source

Although I took full sets of MSI images for all three mummy portraits, I am only going to share a few images of the Portrait of a Young Man (E16213) which proved particularly interesting. The first step of MSI imaging is to take a normal visible light photo using a modified digital camera and appropriate filters. The object and camera setup must remain unchanged throughout the entire process. Only the light source and camera filters change.

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APPEAR Project, Portrait of a Young Man (E16213)                                                                   Ultraviolet visible fluorescence (UVF). Captured with a Nikon D5200, modified by replacing the hot mirror filter with a glass custom full spectrum filter, B+W UV-IR cut filter (#486 MRC), and SPEX Mini CrimeScope 300-400 nm light source.

The ultraviolet visible fluorescence (UVF) image confirms that the wooden panel has been previously repaired. The restored area has a different fluorescence than the surrounding wood (see annotation). I had noticed that the paint in this area was handled differently and noted that it could be a later addition. The UVF image supports this idea.

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APPEAR Project, Portrait of a Young Man (E16213)                                                                         Visible-induced visible luminescence (VIVL) image. Captured with a Nikon D5200, modified by replacing the hot mirror filter with a glass custom full spectrum filter, B+W UV-IR cut filter (#486 MRC), Tiffen red camera filter (23A), and SPEX Mini CrimeScope 535 nm light source.

The most unexpected observation was seen in the visible-induced visible luminescence (VIVL) image captured with a 535 nm light source. The filter gives the image the overall red coloring. Notice that the outline of the figure has been etched into the paint. This demarcation of space was completely undetected under other light sources. This technique was not observed on the other two mummy portraits (E16212 and E16214) at the Penn Museum. I am curious to see if other institutions participating in the APPEAR project have portraits with hidden outlines around their figures.

Be sure to visit the blog in the upcoming weeks to read more about the APPEAR project!

Eve Mayberger, Curriculum Intern

APPEAR Project – Fayum Mummy Portraits

Hi! This is Eve Mayberger and I am a curriculum intern from New York University. I am currently spending nine months at the Penn Museum as part of my fourth-year internship. I want to introduce one of the projects I am working on in the Artifact Lab. The Ancient Panel Painting: Examination, Research and Analysis (APPEAR) project is a Getty Institute initiative to create an international database on Fayum mummy portraits. A website was created to allow different types of analysis and imaging to be uploaded and shared with other institutions participating in the APPEAR project.

The Penn Museum has three Fayum mummy portraits in its collection [E16212, E16213, and E16214]. These portraits date from the Roman period in Egypt and were executed in either encaustic (wax) or tempera. The portraits depict a boy, a young man, and a woman. The figures are painted on thin panels of wood that are adhered together. Remember that wood was a rare and expensive material in ancient Egypt and every tiny piece of wood was valuable.

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APPEAR Project, Portrait of a Boy (E16212)

All three portraits have been repaired at some point in their history. One of my challenges is going to be to differentiate the original materials from later additions. Fortunately, the Penn Museum has the old treatment records that will hopefully be useful to piece together the treatment history of these objects.

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APPEAR Project, Portrait of a Young Man (E16213)

After carefully examining the portraits, I took them down the photography studio in the main conservation lab. These high-resolution photos will be uploaded to the APPEAR website. In the upcoming weeks, I will be using imaging and non-destructive analysis to further investigate these mummy portraits.

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APPEAR Project, Portrait of a Woman (E16214)

Be sure to visit the blog in the upcoming weeks to read more about APPEAR project!

Eve Mayberger, Curriculum Intern

Exploring the painted surface of three coffin fragments

Last week, I wrote about x-raying the fragments of a painted wooden coffin, as part of the conservation treatment. The radiographs helped us see what is under the painted surface. We then turned to the painted surface itself. Through cleaning, we revealed how beautiful and well-preserved the decoration is. I described the cleaning process (and linked to a short video showing the process!) in a previous post.

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E12617A-C coffin fragments before (left) and after (right) cleaning

While it was impossible to see the full range of colors on the boards before cleaning, after cleaning we could see that there were several different colors used to decorate the surface, including two different yellows, red, green, black, and paint that appears black but where it is abraded/damaged looks blue. After much experience working on ancient Egyptian painted wooden artifacts, I knew enough to suspect that some of the paint that appears black is actually Egyptian blue.

It appears that there is a lot of black paint here, but not all of this paint was originally black. The yellow arrows point to black paint while the red arrows point to areas that I believe were originally blue.

It appears that there is a lot of black paint here, but not all of this paint was originally black. The yellow arrows point to black paint while the red arrows point to areas that were originally blue.

If you’ve been reading our blog, you are probably very familiar with one of our favorite photography techniques for Egyptian material, visible-induced infrared luminescence imaging. I have written about it previously, where I explain the process and the equipment we use (follow this link to the post).

Sure enough, it worked beautifully to confirm, and to allow us to see the Egyptian blue on this object:

E12617normaIRfalsecolor

Image of the coffin boards in normal light (left), Visible-induced infrared luminescence image (center), False color image (right). Click on the image to see a full-screen version.

All of the darkened/altered Egyptian blue shows up as bright white in the center image above, and the red areas in the false color image on the right help to further visualize where the blue is in relation to the rest of the painted design. Gotta love this technique!

So that’s great for determining the presence and location of Egyptian blue. But what about some of the other colors? I was particularly curious about the two different yellows and the green. In the case of the yellows, are they two different pigments? And as for the green, which pigment(s) were used to produce this color? Without (for the moment – more about that later) knowing the exact time period of this object, I knew there could be at least a couple different options, including Egyptian green (or green frit), and green earth.

To gather more information about these pigments, I carried out portable x-ray fluorescence analysis (pXRF) in select areas on the boards. I collected data from the following areas, marked with colored X’s in the image below:

pXRF analysis locations, with elements detected listed in order of peak height, from large to small

pXRF analysis locations, with elements detected listed in order of relative peak height, from large to small

As you can see, I labeled the image with the findings from the pXRF analysis. It looks like the two different yellows are indeed two different pigments: the darker, more orange-yellow paint contains primarily calcium and iron, suggesting that this is an ochre, while the brighter yellow paint contains calcium, arsenic, and iron. The relatively large amount of arsenic suggests that this yellow was produced using orpiment (arsenic sulfide).

The green paint also contains arsenic, as well as calcium, copper, and iron. So it appears that the green was produced by mixing an arsenic-containing material (orpiment?) with a copper-containing pigment. Due to the lack of any visible-induced IR luminescence in the green areas, I don’t think that these areas could contain any Egyptian blue, so perhaps the green was made by mixing orpiment with Egyptian green. And as you can see, the blue paint does not contain any arsenic, but does contain calcium, copper, and iron, which we expect to find in areas painted with Egyptian blue. Further analysis will be necessary to determine exactly which pigments were used in the yellow and green areas, but we have discovered a lot using these completely non-invasive techniques!

In my next post about this object, I hope to write about the translation and interpretation, for which I’ll need to consult with the museum’s Egyptologists. In the meantime, if you’d like to learn more about green pigments on ancient Egyptian objects, and more applications of multispectral imaging on Egyptian objects, check out this really great video presentation by Kelsey Museum Conservator Carrie Roberts (originally presented at the 2014 ASOR Annual Meeting):

Green Pigments: Exploring Changing in the Egyptian Pigment Palette from the Late to Roman Periods through Multispectral Imaging and Technical Analysis

Analysis of the shabti box varnish

This is a long overdue post about the varnish on our beloved shabti box (in my last post I referred to the box as troubled…I’ve developed a tiny bit of a love-hate relationship with it, which I’m only now admitting).

A detail of the shabti box before treatment, showing the actively flaking and fractured orange-yellow varnish

A detail of the shabti box before treatment, showing the actively flaking and fractured orange-yellow varnish

Anyway, I’ve briefly mentioned that we believe that the varnish on our shabti box is a pistacia resin, but how did we come to this conclusion? I started out by doing some research into similar objects, and into painted wood from the New Kingdom in general. As I mentioned in a previous post, we know that some painted wooden objects were varnished with pistacia resin during this time period, and these varnishes often look like the coating we see on our shabti box. But there were some things about the coating, including the fact that it was actively flaking, and the fact that there are areas on the box where the paint is lost and where the coating extends over the loss onto the gesso below, which is strange.

In order to start characterizing the coating, I looked at the box under different light sources and did a microchemical spot test, all described here. All roads were leading toward the conclusion that the coating is pistacia resin, but since we had so many available samples (i.e. detached pieces of the varnish) I wanted to investigate further.

First, we turned to a resource that we have in-house: Fourier transform infrared spectroscopy, or FT-IR. FT-IR is a method of infrared spectroscopy, where IR radiation is passed through a sample, and some of the radiation is absorbed and some of it is passed through or transmitted. A spectrum is produced that represents the molecular absorption and transmission, which is unique to that material. I collected samples of detached varnish from the shabti box and from one of the shabti figures, and passed them along to Tessa de Alarcon, a conservator in our department, and consulting scholar Dr. Gretchen Hall. Here is what the spectra look like for each:

FT-IR spectra for samples of varnish from the shabti (top) and the shabti box (bottom).

FT-IR spectra for samples of varnish from the shabti (top) and the shabti box (bottom). The characteristic peaks are labeled on the top spectrum.

They look virtually identical, which confirms that the varnish on the box is the same as the varnish on the shabtis.

Dr. Hall then compared the spectrum for the shabti box sample to spectra for mastic (Pistacia lenticus) and terebinth (Pistacia terebinthus), both pistacia resins.

Spectra for (from top to bottom): the shabti box sample, a sample of terebinth, a sample of mastic from Chios purchased in Athens, and a sample of mastic from Kremer Pigments (the Kremer Pigment mastic sample spectrum was found in the IRUG database). IRUG = Infrared and Raman Users Group

Spectra for (from top to bottom): the shabti box sample, a sample of terebinth collected from the Uluburun shipwreck, a sample of mastic from Chios purchased in Athens, and a sample of mastic from Kremer Pigments Inc. (the comparative spectra were found in the IRUG database, IRUG = Infrared and Raman Users Group)

They all look very similar, with characteristic resinous acid peaks that occur between 1700 & 1720 cm-1 (carbonyl stretching) & the acid OH stretching that occurs ~1460 cm-1.

In order to see if we could classify the shabti box resin even further, Dr. Hall took a sample to Dr. Chris Petersen, Affiliated Associate Professor in the Winterthur/University of Delaware Program in Art Conservation (WUDPAC), where they analyzed it using Gas Chromatography-Mass Spectrometry (GC-MS). GC-MS is a technique that combines 2 methods of analysis, and in conservation we use it to analyze organic compounds.

Dr. Hall and Dr. Petersen ran the sample and here is what the GC-MS chromatogram looks like:

L-55-23A_GCMSlabeled2Dr. Petersen labeled the peaks and included their structures. The structures are consistent with pistacia resin, either mastic or terebinth. They did identify a peak for 28-norolean-17-en-3-one (#3 above), characteristic of heated pistacia resin, which could indicate that the resin was heated before application (which would have turned it from clear to a yellowed varnish). We cannot be certain what color the varnish was when it was first applied, but the analysis does confirm the fact that the shabti box and the shabtis all have aged pistacia resin coatings.

We are grateful to both Dr. Hall and Dr. Petersen for their work on this analysis!

 

Is there an archaeobotanist in the house?

Fortunately for us, the answer is yes.

Following up on my recent post about identifying the wood used to make this Middle Kingdom painted wooden coffin, I showed the images of the thin sections I cut from some detached wood fragments to Dr. Naomi Miller, our resident archaeobotanist. Dr. Miller typically deals with really degraded material, often tiny pieces of charcoal, so she was delighted to see that these samples showed enough information to make a more definite identification. AND, much to my delight, she confirmed my hunch that these boards are made of acacia.

Here are the images she used for comparison, found in Anatomy of European woods, by Fritz Hans Schweingruber.

acacia references

Reference images of Acacia cross-sections (left) and tangential sections (right)

And here they are, side-by-side with our samples:

wood comparison cross sections

In the cross-sections, we see pore multiples and uniseriate rays

wood comparison tangential sections

In the tangential sections, we see mostly uniseriate rays, with some biseriate rays.

We compared our samples’ images with images of ash and carob in the same book, since these were also candidates originally, but there were enough differences for us to exclude these as possibilities. It is possible that there is something that we are not considering, but I think that I’m convinced by this work that this coffin was made with acacia.

 

Wood ID

I’m currently treating 7 fragments of a painted wooden coffin from Abydos. Lately, many of our visitors have been asking what kind of wood was used to make this coffin. This has actually been a question that we have been asking ourselves, and we are trying to see if we can come up with an answer.

In ancient Egypt, large timbers for coffin-making were scarce, so the wood was either imported from places like the Mediterranean, the Near East, or from other parts of Africa, or the Egyptians would cobble together smaller pieces of wood from local sources. Based on previous studies, we have a finite list of types of wood that are known to have been used, but from there we need to move to looking at the object itself.

These images show the exposed wood on the side (left) and back (right) of one of the coffin fragments. Can you guess what type of wood this might be?

These images show the exposed wood on the side (left) and back (right) of one of the coffin boards. Can you guess what type of wood this might be?

As conservators, we are educated not only in object treatment, but in the analysis of objects, and the examination of tiny fragments of objects, like plant and textile fibers, wood, and pigments. But many of us don’t do wood ID all that often, so it can take awhile to get set up, to re-orient ourselves to what we’re seeing in the samples, etc. AND it requires a sample, which we don’t often have access to. Fortunately, for me, I have some already detached samples from these boards and access to someone who does this type of work more frequently, archaeobotanist Dr. Naomi Miller, so I turned to her to help me with this work.

Dr. Miller looked at the samples I had and selected one that looked promising, due to the exposed cross-section on one end. I mounted this sample under our binocular microscope and took a photo, to help her study it further and compare to known reference samples.

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The wood fragment with exposed cross section, 60X magnification

From this sample, Dr. Miller was able to determine that this is a hardwood, based on the presence of clearly visible rays and thick-walled pores, many of which are radially paired (pointed out below).

Slide4Based on these features and the known types of hardwoods used in ancient Egypt, this helped narrow down the likely possibilities to Common ash (Fraxinus excelsior L.), Carob (Ceratonia siliqua L.) and Acacia (Acacia sp.). Dr. Miller considered other types but ultimately excluded willow (Salix), oak (Quercus), elm (Ulmus) and sycamore fig (Ficus sycomorus) due to either the presence or absence of certain features.

In an attempt to further narrow down the possibilities, I cut thin sections from the sample that Dr. Miller examined, from the cross-section and tangential surfaces, and wet-mounted them on glass slides. Looking at these thin sections with our polarizing light microscope (PLM), I was able to see some of these features a bit more clearly.

Cross-section, 50X magnification

Cross-section, 50X magnification

In the cross-section above, the pores are visible as solitary or paired, and mostly uniseriate (1-cell wide) rays are visible. The tangential section also shows mostly uniseriate rays, but some bi-seriate rays are visible as well.

Tangential section, 50X magnification

Tangential section, 50X magnification

Cutting these sections from the wood sample, which was quite degraded, was difficult and unfortunately I’m not really able to pick out many other features from the sections that I examined. I will have to get Dr. Miller to weigh in on this again, but in the meantime, I’m going to go out on a limb and say that I’m leaning toward this wood being acacia. One thing I forgot to mention is that the wood of the coffin board fragments is a deep red-brown color. Acacia is known for being a red, hard, and durable wood, and while it produces small timbers, we know that it was used for coffin-making, among other things.

Peptide Mass Fingerprinting (PMF)

Motivated to learn more about the fur and animal hair found in our Predynastic mummy bundle, I popped up to Boston yesterday for a workshop entitled “Identifying collagen-based materials in cultural objects using peptide mass fingerprinting“.

The workshop was organized by a group at Harvard, including the Peabody Museum of Archaeology and Ethnology in collaboration with the Straus Center for Conservation at the Harvard Art Museums and the Harvard FAS Division of Science. The team received NCPTT funding for a project to develop a new application of an analytical technique called peptide mass fingerprinting (PMF).

PMF uses mass spectrometry to analyze very tiny samples of proteinaceous objects and identify the mammalian source to the species level. It actually can be used to analyze materials made of collagen and keratin, but the group at Harvard is focusing on collagen-based materials. The procedure essentially breaks up the protein into smaller peptides, and the mass of the peptides is measured using a mass spectrometer such as a MALDI-TOF. The peptide masses are compared to known reference samples, which allow for identification. This type of analysis falls under the category of proteomics, or the large-scale study of proteins, and it is sometimes referred to by this name as well.

The Harvard project is focused on applying this technique to objects made of gut, skin, sinew, and membrane from Alaska, the Northwest Coast, Northern California, and the High Plains. Another goal of the project is to bring this type of analysis, which typically takes place in large industrial or academic labs, to museum labs. You can learn more about the project on their blog.

The workshop included 3 presentations by the project’s primary analytical investigator/scientist Dr. Dan Kirby, project research associate Madeline Corona, and Kress fellow Ellen Promise. Between the 3 of them, they covered how PMF works, what it can tell you, and how it is applied to cultural artifacts, using a project on Alaskan kayaks as a case study.

After Q&A led by Peabody Museum conservator T. Rose Holdcraft, we were led on a tour of the Peabody conservation lab, where we were able to feast our eyes on some of the impressive Native Alaskan objects that they are investigating as part of the project.
A view of the Peabody Museum conservation lab, with several Native Alaskan skin and gut objects on view

A view of the Peabody Museum conservation lab, with several Native Alaskan objects on view

We also toured the impressive Mass Spectrometry and Proteomics Resource Lab, where we had a chance to see the Bruker MALDI TOF/TOF instrument and a demonstration of how samples are prepped for analysis.
The Bruker MALDI-TOF/TOF instrument and Madeline Corona demonstrating sample prep

The Bruker MALDI-TOF/TOF instrument and Madeline Corona demonstrating sample prep

The sample prep area showing the equipment used, including the MALDI plate (lower right)

The sample prep area showing the equipment used, including the MALDI plate (lower right)

Here at Penn, we are excited by this technique – not only for the minute sample size required (the samples used are just barely detectable to the naked eye) but also for its accessibility. We have a lot of animal-based materials in our collection and we are hoping to pursue using PMF to analyze these materials. Actually, we are already working to see if its possible to use this technique to identify the sources of the fur and basketry hair fibers from our Predynastic mummy, thanks to help from Smithsonian MCI fellow Caroline Solazzo, whose work focuses on keratin-based materials. PMF supposedly works on all types of samples, including those that are very old and/or are in poor condition, so we thought we’d put this to the test by starting with samples from our oldest Egyptian mummy (he’s well over 6000 years old). We will let you know how it seems to work.

A side note – a quick trip to Boston wouldn’t be complete without a stop at the Museum of Fine Arts. I spent most of my time there ogling the Ancient Egypt exhibits, admiring the massive, yet delicately decorated and inscribed coffin boards of Djehutynakht’s outer coffin (same time period and style as Ahanakht’s coffin)

The interior of the lid of Governor Djehutynakht's outer coffin (left) and detail of the false door (right)

The interior of the lid of Governor Djehutynakht’s outer coffin (left) and detail of the false door (right)

and many of the other treasures of this collection, such as this bead net dress made of faience and gold from the 4th Dynasty.
Detail of a 4th Dynasty beadnet dress (ca. 2551-2528 BCE)

Detail of a 4th Dynasty beadnet dress (ca. 2551-2528 BCE)

Breathtaking, really. I also found this shabti in a miniature coffin very charming.
Shabti of Queen Neferu with  miniature coffin, from Deir el-Bahri, tomb of Queen Neferu, 11th Dynasty (ca. 2061-2010 BCE)

Shabti of Queen Neferu with miniature coffin, from Deir el-Bahri, tomb of Queen Neferu, 11th Dynasty (ca. 2061-2010 BCE)

And while the MFA does not have conservators working in a gallery, as we are doing here at Penn, they do have some great “behind the scenes” galleries, one with interactives that engage visitors to think about conservation ethics and decision making. One of my favorites was an example using Maya Cylinder vases, examining condition issues and treatment decisions.

Some screen shots of the Maya vase example in the MFA's "behind the scenes" gallery

Some screen shots of the Maya vase example in one of the MFA’s “behind the scenes” galleries

All in all, a great trip. We’ll keep you updated on the whole peptide mass fingerprinting technique and how we might be able to use this for our collection.

 

More about our Predynastic mummy

Last year we posted some information about Bruce, our Predynastic mummy (and the oldest Egyptian mummy in the museum) here in the lab. Bruce has been on ongoing project, but he is often tucked toward the back of the lab unless we are actively working on him. While he’s often not front-and-center, when visitors enter the gallery and they catch a glimpse of him, they know that he’s special, even if they don’t know what he is, exactly.

Bruce on his cart, near the back of the lab, as viewed through the Artifact Lab windows.

Bruce, near the back of the lab, as viewed through the Artifact Lab windows.

As soon as he is spotted, I am often asked “what is that?” “is that a mummy?” and “what are you doing with him?”. In conservation, we are not always actively treating objects (or in this case, mummies); some of our projects involve close examination and study of objects (often referred to as technical studies). These technical studies may be a precursor to conservation treatment, but they may also be independent of treatment.

We are not currently carrying out conservation treatment on Bruce. Our focus at the moment is careful examination and some analysis, in consultation with other specialists. At the moment, we are focusing on trying to identify the type of animal hide that he’s wrapped in:

The red arrows are pointing out pieces of the animal skin bag wrapped around Bruce.

The red arrows are pointing out pieces of the animal skin bag wrapped around the mummy.

and also the animal hairs used to make the finely woven baskets included in his burial bundle:

E16229_basketsThese baskets are actually made of plant and animal fibers – the baskets are twined, and the passive elements (or warps) are made of plant fibers, while the active elements (wefts) are made of light and dark animal hairs. We know that the wefts are animal hairs based on our examination of these fibers using our polarized light microscope (PLM).

Views of the light-colored hair (left) and a cross-section of the hair (right) at 100X magnification

Views of the light-colored basketry fiber at 10X (upper right), at 50X (lower left), and a cross-section (lower right) at 200X magnification

Views of the darker hair (left) and a cross-section of the hair (right) at 100X magnification

Views of the darker basketry fiber at 10X (upper right), at 100 X (lower left), and a cross-section (lower right) at 200X magnification

Sometimes animal hair can be identified based on the features observed under a microscope, by comparing the unknown hairs to known reference samples. Some great animal hair ID sources on the web include this great resource on the FBI website and the Alaskan Fur ID website.

While we can clearly see that these fibers from the basket are animal hairs, we have not been able to identify them based on microscopy alone, so we are pursuing other analytical methods of identification, such as peptide mass fingerprinting (PMF). PMF uses a mass spectrometer to analyze the peptides in a proteinaceous sample, which can identify mammalian material to the species level using a micro-sized sample. Next week, I am attending a collagen identification workshop at Harvard, where I will learn more about PMF and its application to cultural artifacts.

We are excited by the possibilities this technique offers – being able to identify the skin(s) Bruce is wrapped in and the materials used to make the baskets found in his bundle will add to our understanding of very early technologies and funerary practices in Egypt. We will certainly share our findings as we learn more.

 

Investigating the shabti box coating

Last month, I wrote about a new challenge in the lab, otherwise known as this shabti box and its associated shabtis:

front compressedAt first the box came into the lab with 3 shabtis, and then we found that there were 3 more in storage that may belong with the box as well. 4 of the shabtis are very similar in appearance whereas the other 2 are slightly different, so they may actually not be associated after all. Can you spot the 2 different shabtis?

2 of these things are not like the others...

2 of these things are not like the others…

All of these objects are made of wood, gesso, and paint. And as you can see, all of them have an orange-yellow coating on their surfaces. In my last post I posed the questions “what is this coating?” “is it an original varnish or is it a later restoration?”. My initial guesses were that it is either an original pistacia resin varnish, a later cellulose nitrate (or other old restoration adhesive) coating, or a combination of the two.

Well, there are several things we can do to try to answer these questions and to narrow down the possibilities. One of the first things I did was to look at these objects very carefully using our binocular microscope. I could see that the coating was applied unevenly, especially on the box, and that it is actively cracking and flaking. Another thing that I noticed was that there are areas on the box where the paint is lost and where the coating extends over the loss onto the gesso below.

A detail shot of one side of the shabti box - the yellow arrows are indicating areas where the coating extends over an area of paint loss onto the gesso.

A detail shot of one side of the shabti box – the yellow arrows are indicating where the coating extends over areas of paint loss onto the gesso.

Usually, this would indicate that the coating was applied after the damage occurred (so sometime after excavation, either in the field or soon after coming to the museum). So this is one clue, but doesn’t really answer my questions.

Next, I examined the shabti figures under ultraviolet (UV) light. In conservation we routinely use UV examination to characterize materials and to distinguish old restoration materials from original materials – for instance, shellac, used historically to repair objects, exhibits a characteristic bright orange fluorescence under UV. (For a great explanation of UV, along with some interesting images, check out this post on UV examination by my colleague Allison Lewis, conservator at UC Berkeley’s Phoebe A. Hearst Museum of Anthropology.)

The coating on the box and the shabtis has a yellow-orange appearance under UV – but not the bright orange that we expect to see from shellac.

shabti UV

4 shabti figures under UV light

So UV examination was helpful (it eliminated shellac as a possibility) but didn’t answer my questions either.

Next, I did a microchemical spot test on a couple of the previously detached flakes of the coating. We’ve used spot-testing before in the lab – the last time I wrote about it was in reference to the mystery fibers on Tawahibre’s coffin. In this case, I carried out a spot test for nitrates using diphenylamine (according to instructions in Material Characterization Tests for Objects of Art and Archaeology). Using this test, a sample containing nitrates will turn blue once a solution of diphenylamine/sulfuric acid is added. Below you can see the result of the test on one of the coating flakes from the shabti box (left) and the test on a control sample of cellulose nitrate adhesive (right).

Left: coating sample from the box after spot test (negative result) Right: control cellulose nitrate adhesive after spot test (positive result)

Left: coating sample from the box after spot test (negative result) Right: cellulose nitrate control after spot test (positive result)

Based on these results, it seems that the coating does not contain cellulose nitrate. This does not mean that the coating does not contain another recently-added adhesive. We have a few other ways of narrowing down the possibilities even further, and I will write about our continued work on this in my next post.