Reimagining an ancient Egyptian material

Posted on April 30, 2013 by mollygleeson

Have you checked out our In the News section of this blog? Periodically, we try to update this page with some interesting articles related to our Egyptian collection, stories about projects and discoveries in Egypt, and even our own lab highlighted in the press.

One of the more recent stories that we’ve posted is about a new discovery related to Egyptian blue, one of the world’s first synthetic pigments. The ancient Egyptians made it by heating together copper, silica (sand), lime (calcium oxide) and an alkali such as natron (sodium sesquicarbonate) and it is found on objects from as early as the 4th Dynasty through to the Roman Period. We see this pigment on artifacts here in the lab, including Tawahibre’s coffin (and for more details read our blogpost on how we know this.)

A detail of Tawahibre’s coffin. Based on analysis, this pigment has been determined to be Egyptian blue.

One thing that has been discovered about Egyptian blue is that it has luminescent properties-this luminescence cannot be seen in normal light conditions, but can be detected using infrared light. Using an infrared light source, it is possible to not only positively identify Egyptian blue using a completely non-invasive technique, but it is also possible to discover very small traces of Egyptian blue pigment on surfaces of objects. The British Museum provides a great overview of this phenomenon on their website. It is our hope that we might be able to try this technique to examine some of the artifacts in our collection.

A painted wood uraeus on display in our Upper Egypt gallery. The paint has not been analyzed, but based on appearance the blue is most likely Egyptian blue. Examination with an IR light source could confirm this.

Furthermore, it is now understood that this luminescence is produced by the nanostructure of the pigment – scientists have discovered that the calcium copper silicate in Egyptian blue can be broken into nanosheets, which produce infrared radiation similar to beams that communicate between TVs and remote controls and car door locks. It is now being envisioned that these nanosheets could be used for future near-infrared-based medical imaging techniques and security ink formulations!! Talk about a new life for such an ancient material.

You can read and hear more about this by following this link to our In the News section of this blog. Have you read or heard about something recently that you think we should share on our blog? Leave a comment here and we’ll try to incorporate these suggestions whenever possible.

Tawahibre all tied up

Posted on April 13, 2013 by mollygleeson

When I wrote about the fantastic image we retrieved from our Archives a couple weeks ago showing our Mummy Gallery in 1935, I promised to provide an update on the treatment progress on Tawahibre’s coffin.

Well, why don’t I start with this:

A view of Tawahibre’s coffin from above

While you may not be sure what you’re looking at here, this looks like progress, doesn’t it? I’ll tell you what you are seeing – the coffin is tied in several places with cotton twill tape, holding small pieces of white Volara foam and blueboard (acid-free, lignin-free corrugated board) in place against the coffin surface.

A detail of the Volara foam and blueboard held in place with cotton twill tape

The purpose of this system, other than looking kind of intriguing, is to place select pressure in areas on the coffin (whenever I say this I always think of the useful book The Gentle Art of Applied Pressure-the title speaks for itself). As I have described previously, the coffin is pretty distorted in areas, due to the fact that many of the individual wood elements have separated and moved apart and that the plaster has separated from the wood substrate. We are trying to realign these pieces as much as possible using humidification with a Preservation Pencil, which allows us to direct a small stream of warm humidified air in select areas, which helps the plaster and wood relax a bit and encourages movement. Once we get an area to move sufficiently, we then apply pressure to the area to hold everything in place.

Here Nina is directing a stream of humidified air with the Preservation Pencil and I am applying pressure with my hands.

We’re also continuing to consolidate the painted surface and readhere loose pieces of plaster and wood.

We don't usually work in teams, but yesterday we had a little group humidification and consolidation party!

This treatment has been a team effort, and yesterday we had a little group humidification and consolidation party!

While we’re making progress and becoming pretty comfortable with the coffin and the treatment, there are still some scary areas to deal with. This is an area that I’ll be tackling next:

A detail of a badly damaged area on the coffin, showing significant cracking and flaking and detached and displaced fragments

Wish us luck as we continue this work!

From the Archives

Posted on April 3, 2013 by mollygleeson

The Penn Museum Archives is an incredible resource for us here at the museum.

A view into the Penn Museum Archives

When we begin working on objects in the conservation lab, we carry out preliminary research, which often includes searching for related materials in the Archives. Among the materials we may be interested in are archaeological field notes, letters between curators and archaeologists or collectors about the acquisition of specific artifacts, and old photographs.

Recently, Senior Archivist Alex Pezzati scanned some images for me, including this one, a shot of the Egyptian “Mummy Gallery” in 1935.

I was excited to see some of the artifacts we’re working on in the Artifact Lab right now in this photo. Can you pick some of them out? In the image below I’ve circled some of them in red.

The objects circled in red above are either being worked on in the Artifact lab or are on display in our accompanying exhibit

These old exhibition photographs can be extremely valuable to conservators. Not only does this particular image tell us that certain artifacts were definitely on display, and when (which may not be recorded elsewhere), but it also shows us how they were displayed. In some cases, seeing the way that artifacts were previously displayed may help to explain damage, such as excessive fading on one side or adhesive residues left behind by an old mount. We can often make good guesses about this type of damage, but it’s always nice to have some proof!

What particularly excited me about this photograph is that it shows the coffin of Tawahibre in the gallery. We are currently working on this coffin in the lab, but it is still too fragile to separate the lid from the base to allow for examination of both pieces individually.

The coffin of Tawahibre in the Artifact Lab.

Just recently, Curator Dr. Jen Wegner was up in the lab and we were discussing the coffin and some of my observations, and she wondered out loud if the back had any text written on it. I had wondered the same thing myself but I knew that until we carried out further work, we wouldn’t be able to know.

BUT, since this 1935 photograph shows both the lid and the base of the coffin on display, we don’t have to wait any longer!

The lid and the base of Tawahibre’s coffin, side by side in the Mummy Gallery in 1935.

As you can see in the above image, there is writing on the back! Now only if we could just hasten the conservation treatment so we can examine it for ourselves…

Another thing that is useful about this image is that is shows that much of the damage we’re seeing on the coffin today was present in 1935. This includes both major structural damage and extensive paint loss in areas. It is likely that the coffin came into our collection with this damage, which is somehow reassuring to me. I will also note this in my documentation.

Tawahibre’s coffin in 1935 (left) and today (right). Much of the major damage we see today had already occurred by 1935. To highlight this, I’ve circled some of the damaged areas in red in both images.

We continue to plug away on the treatment of the coffin and we are hoping to soon reach the point where we can separate the lid. I will provide an update shortly about some of the more recent work we have been carrying out on this artifact!

Mystery fiber

Posted on February 23, 2013 by mollygleeson

In a recent blog post I mentioned that I am working on the painted coffin of Tawahibre, which has fibers mixed into the ground layer (gesso). In my examination prior to starting treatment, I had noted these fibers, and observed that they are present all over the coffin lid, mixed into the ground layer just below the painted surface. They are exposed in many places where there are losses-here is an image of one area where the surface of the coffin is badly damaged, revealing these fibers:

Fibers visible in the ground layer of the painted coffin lid

There are quite a lot of these fibers in some areas (as seen in the photo above), and then in others, there are very few. They are found in areas where the ground is thick and also where it is applied very thinly. They are not arranged in any particular way-they appear to have been mixed haphazardly into the ground. The fibers are light brown in color, and while most of them are very stiff, they react almost immediately to moisture, becoming very flexible when wet. I had initially assumed that these were plant fibers-possibly flax-but they always seemed a bit odd, and to be honest, these fibers remind me a little bit of sinew (animal tendon).

As I have been working on the coffin, several of these fibers “presented themselves to me” for sampling-meaning, as I’ve been working to stabilize some of the areas with these fibers, a couple became detached, allowing me to investigate them further using PLM. So far I have looked at 2 samples, and both look the same. I prepared the fibers by mounting each one on a glass slide with water. When looking at them in plane-polarized light, they look like this:

Two different fibers from the coffin ground layer viewed at 50X magnification

I didn’t really know what I was seeing-it was difficult to pick out any really distinguishable features, so I then viewed both fibers under crossed polars. This is what I saw:

Same two fibers viewed under crossed polars at 50X magnification

What the heck is that? I’ve never seen anything like this before. When I showed this to a few other people, the first reaction has been-it looks like a worm! And it totally does. This very regular banding pattern has got to be characteristic of something-I just don’t know what.

I thought I had a lead last week-I found this image in a book, showing a bundle of sisal fibers with a commonly-seen spiral element:

Sisal sample showing a characteristic spiral element. Image from “Color Atlas and Manual of Microscopy for Criminalists, Chemists, and Conservators” by Nicholas Petraco and Thomas Kubic, p. 94.

However, just last week I obtained a sisal sample from one of the Winterthur art conservation graduate students and I’m pretty sure that’s not what I have. The sisal sample looks distinctly different to me-here it is in both plane polarized light and under crossed polars:

Sisal reference viewed at 400X magnification in plane polarized light (left) and crossed polars (right). Also, note the difference in magnification between these fibers, viewed at 400X, as opposed to the coffin mystery fibers above, viewed at 50X.

For the moment, I’m stumped. But I’m continuing to investigate this and to get input from colleagues, and I’m open to suggestions/ideas! I’ll also certainly provide more information when I know more. To be continued…

A sticky issue: choosing a consolidant for our painted coffin

Posted on February 9, 2013 by mollygleeson

In a previous post, I described some of the issues we’re facing in the treatment of our painted coffin of Tawahibre.

The top of the coffin before treatment – note the large losses and areas where the paint and gesso are just barely hanging on by a (plant fiber) thread

We’ve managed to clean much of the painted surface, but there are many areas of the paint and gesso that are so fragile, you get the feeling that a deep exhale – not to mention a sneeze – would send fragments flying. (And when I say gesso, I’m referring to the calcium carbonate preparatory layer/ground, which has plant fiber inclusions, that I’d like to investigate further).

Such areas require consolidation. We use this word, consolidation, a lot in conservation, and many of our treatments involve this process. Consolidation is essentially the reunification/reinforcement of a weak or powdery substance through the application of a material that we refer to as a consolidant. Consolidants often consist of dilute adhesive solutions, and they may be applied directly to artifacts with a brush or syringe, by spraying onto the surface, and in some instances, it may be appropriate to immerse an artifact in a consolidant solution. Ideally, a good consolidant must be stable (good aging properties), reversible (can be removed if necessary), and should not change the appearance of the artifact.

We have mixed up a variety of consolidant solutions to have on hand in the Artifact Lab – here are a few, along with some brushes, a plastic pipette, and syringes

Choosing an appropriate consolidant requires testing ahead of time. To start, it is important to test a variety of solvents (such as water, acetone, ethanol) – knowing which solvents can be used safely on a particular artifact will likely narrow down the range of adhesives that can be used (due to the fact that many adhesives are only soluble in a select number of solvents). In the case of our painted coffin, this involved testing all of the colors of the painted surface as well as the gesso substrate. Testing was carried out by rolling a swab dampened with each solvent over a discreet area and then observing the area for changes.

Solvent testing on an area of blue paint

After carrying out these tests, I did some research into what other conservators have used successfully for similar treatments on similar artifacts. In our field, we are fortunate to have a good body of published literature, and there is increasingly more information that can be found on the web as well. The sources I referred to included articles in the Journal of the American Institute for Conservation (JAIC), and a variety of books that have been published on the subject of conservation of Egyptian collections. Websites/blogs that I have found really useful include Inside the Conservator’s Art: A behind-the-scenes look at conserving Egyptian artifacts at the Phoebe A. Hearst Museum of Anthropology, conservator’s entries on the Brooklyn Museum blog, and the British Museum’s online collections database, which has many records with detailed conservation treatment information. There are actually lots of great blogs and websites out there, and I am grateful to my colleagues for actively sharing information in this way.

After this work, I selected several consolidants, and conducted another round of testing. During my testing I discovered that water was the key to getting the paint and the gesso to relax. Unfortunately, the painted surface is sensitive to water, but I found that a 50:50 mixture of water and ethanol is acceptable for use, especially when applied in a solution behind the lifting paint. In the end, we’ve chosen to consolidate the very fragile paint with a solution of methyl cellulose (a water-soluble cellulose ether) in a 50:50 water/ethanol mixture. To re-adhere larger flakes and chunks of gesso, we are experimenting using higher concentrations of methyl cellulose alone, and in combination with other adhesives, including Lascaux, a water-based acrylic resin.

An area near the foot of the coffin, before (left) and after (right) readhering detached gesso and consolidating paint

As I’ve stated before, this will be an ongoing project in the Artifact Lab – we will continue to report on our treatment progress, and any interesting discoveries made along the way (which is inevitable!).

In the Artifact Lab

Tag Archives: Tawahibre

Reimagining an ancient Egyptian material

Tawahibre all tied up

From the Archives

Mystery fiber

A sticky issue: choosing a consolidant for our painted coffin