Laser cleaning a trio of birds

In addition to the frieze of 6 bulls (which we are still working on in the Artifact Lab), we are also treating a frieze of 3 birds, in preparation for our new Middle Eastern Galleries, scheduled to open in April 2018.

B15883, frieze of 3 birds before treatment

This is a section of a frieze from the site of Al-Ubaid, Iraq which was excavated by Sir Leonard Woolley in the early 1920s. The birds are the only original pieces of the frieze – the rest is a modern reproduction. The birds (possibly doves?) were carved from limestone and each has a pair of drill holes at their center which would have served as an attachment point. Copper alloy twists would have been used to secure the birds in antiquity – fragments of the original copper remain in one of them.

Due to structural stability issues in the modern reproduction, we needed to disassemble the entire frieze. Once the birds were removed, it was evident that their surfaces were very grimy, related to both the burial environment and time in museum storage. A variety of cleaning methods were explored and tested, but none worked better than using our laser.

One of the birds, after removal and before cleaning

The Conservation Department purchased a Compact Phoenix Nd:YAG laser several years ago, and we are still learning about all of its possible applications. We recently had a workshop with conservator and laser-guru Adam Jenkins, which helped us further develop some testing and health and safety protocols.

Essentially, the Nd:YAG laser works like this: the laser emits a beam of light, typically with a wavelength of 1064 nm (in the infrared), which selectively irradiates and removes unwanted dirt and surface coatings without damaging the object (a process called laser ablation). This type of laser cleaning works well for removing dark substances from light-colored objects, so trying it on one of the birds made a lot of sense.

Easy for me to say. I didn’t do this treatment – project conservator Madeleine Neiman did. So she gets all the credit for this.

After testing, Madeleine carried out her first laser cleaning treatment on the bird in the image below. Here she is getting set up to carry out the work:

And here is a shot of the bird after the surface was partially cleaned: (WOW!)

I think the process and results are best displayed in a gif, or a video, so I’m including the gif below, and here is a link to the video.

Go Madeleine! I think this was a really rewarding treatment to carry out. Please take note of all of the PPE (personal protective equipment) involved, including special eyeware and ventilation.

CAAM takes over the Artifact Lab (for a day)

If you visit the Artifact Lab tomorrow (Tuesday August 22) during our open window sessions, you’ll be in for a treat. Instead of speaking with one of us (the conservators) you’ll have the opportunity to chat with two of our CAAM* teaching specialists, Dr. Kate Moore, Mainwaring Teaching Specialist for Zooarchaeology, and Dr. Marie-Claude Boileau, Teaching Specialist for Ceramics. We frequently consult and collaborate with them, but this will be their first time working behind the glass walls of the Artifact lab for our open window sessions.

Dr. Kate Moore and Dr. Marie-Claude Boileau in the Artifact Lab

They look ready for anything, don’t they? Don’t miss this unique opportunity (between 11:00-11:30am and 1:30-2:00pm) to ask them questions and talk to them about their work and research!

*CAAM, which stands for The Center for the Analysis of Archaeological Materials, is a joint endeavor between the Penn Museum and the University of Pennsylvania’s School of Arts and Sciences (SAS)

A lion relief from Nippur

Yesterday we received a new artifact in the lab: this terracotta lion relief from Nippur, Iraq.

B20014: the lion relief in fragments

Some may argue that this object could be a candidate for the Ugly Object of the Month club. Well, we like him, and one of our conservators pointed out that he looks a lot like one of these wonderful characters from William Steig’s Rotten Island.

Illustration from William Steig’s “Rotten Island”. Image courtesy of scienceblogs.com

This relief was excavated in the University of Pennsylvania’s Babylonian Expedition to Nippur in 1899. Like the Nippur slipper coffin currently on display in the Artifact Lab, it was previously repaired with metal staples and (at least one type of) adhesive, likely around the same time as the slipper coffin.

The staple-like wire tires used to repair the relief are visible in this view of one of the break edges.

More evidence of the old repairs on this fragment.

Getting this relief ready for exhibition in the Middle Eastern Galleries will not only require significant conservation treatment, but also a custom mount so that it can be displayed safely. We will provide updates as we work on this.

Update from the Gordion Excavations

Julia Commander is a third-year graduate student in the Winterthur/University of Delaware Program in Art Conservation. She is currently completing a curriculum internship at the Penn Museum.

In my last post, I introduced the Gordion Archaeological Project and what I’ve been up to as a conservation intern here. The season has continued at a quick pace, with a steady stream of incoming small finds and projects at the Gordion Museum.

While some objects only require a light cleaning, others can take a few days to process. I mentioned two pairs of copper alloy tweezers, and second pair has now been fully treated. In addition to mechanical cleaning, the copper alloy object was treated with the corrosion inhibitor benzotriazole, also called BTA. Objects are immersed in the solution and placed in a vacuum chamber to ensure effective application. The corrosion inhibitor is then protected by a coating of dilute acrylic resin. After these treatment steps, any structural breaks can be reconstructed and joined with an adhesive. For objects with weak points that may be susceptible to further breakage, small supports can be added to the housing. Here I included an Ethafoam support with a cavity cut out to hold the pair of tweezers.

Copper alloy objects are rinsed with acetone prior to treatment with BTA, a corrosion inhibitor.

Copper alloy objects drying after treatment. This group includes an arrowhead, a fibula, tweezers, and a decorative fitting.

Another example is this small ceramic figurine fragment. In this case, the female figure has a stable structure but a very delicate pigmented surface. The pigment was consolidated with a dilute adhesive mixture, applied by pipette to avoid any action on the surface. To further protect the surface, the figure was cavity packed with a layer of smooth Tyvek, which will prevent abrasion and further pigment loss.

Ceramic figurine fragment in protective housing, made from an Ethafoam cavity with smooth Tyvek barrier.

Processing small finds often involves unexpected discoveries. While working on a small ceramic vessel, I was interested to learn what was contained inside. One of the best parts about working on site is the opportunity for immediate collaboration. After talking about the soil samples with an archaeobotany student, I knew to expect small bones in the vessel interior, potentially from a mouse. After pulling out many, many vertebrae and rib bones, I consulted our zooarchaeologist to figure out what the bones may be. There were no signs of a skull, which likely deteriorated further due to its fragility. However, the other bones indicated not a mouse but a snake coiled inside the vessel. We can’t say what the snake was doing there, but all the associated bones and soil will be kept for potential further study.

Excavating the interior of a small intact jug.

Small rib and vertebrae bones, likely from a snake, from the interior of the jug.

During the season, we’ve also had some very large finds in the active excavation areas. This includes a large ceramic pithos that was found almost completely intact. In this case, conservation made several site visits to consult about techniques for supporting and lifting the object. After padding the interior of the vessel, we added supportive wrapping over a thick layer of dirt that was left as protective casing. This process helps minimize damage from physical forces and also keeps fragments in place if they happen to detach.

As I get ready to wrap up my time here at Gordion, I was lucky to have the opportunity to see the site from a new perspective. Along with several colleagues, I was able to take a hot air balloon ride over Yassıhöyük and some of Gordion’s many burial mounds.We enjoyed magnificent aerial views of our workspace!

Aerial view of the citadel mound with active excavations.

Hello from Gordion!

Julia Commander is a third-year graduate student in the Winterthur/University of Delaware Program in Art Conservation. She is currently completing a curriculum internship at the Penn Museum.

As part of my internship year, I’m spending a month at the Gordion Excavations in the small town of Yassıhöyük, Turkey. This site, the capital city of ancient Phrygia, has been excavated by the University of Pennsylvania since the 1950’s. As a student interested in archaeological conservation, gaining experience with material in the field is an exciting learning process.

The Gordion dig house.

The conservation lab within the dig house compound.

Our home base is a small lab in the dig compound, where we work on processing whatever the excavators find. This year, we have a large amount of iron and copper alloy material. The metals are corroded and fragile, but many retain interesting details and clues about their use. Some of my favorite small finds so far are these two pairs of copper alloy tweezers, including a miniature version! Cleaning involves mechanical removal of dirt and corrosion products, followed by the application of a corrosion inhibitor for the copper alloy.

Two pairs of tweezers recovered as small finds and modern tweezers for scale. The miniature pair (left) has already been treated by reducing dirt and corrosion products.

We also consistently have a lot of ceramic material. Most of the ceramics are washed, sorted, and stored as bulk pottery, although particularly significant or interesting fragments come to the lab. This category includes painted tiles, inscribed or elaborately decorated fragments, and vessels that can be reconstructed. In the lab, we set up containers for desalination treatments, where ceramics are soaked in filtered water to slowly reduce salt content. These salts came from the burial environment, and they can cause damage over time if they remain in high concentrations. The process factors in ceramic weight, water volume, and time to tailor a treatment plan for each object.

Desalination set-up. Each container holds a ceramic object or fragment, and the soaking process reduces salts in the material.

In addition to keeping up with the current excavations, the conservation team works on projects with researchers and the local Gordion Museum. For researchers, accurately recording artifacts often involves detailed measuring and drawing. Conservators contribute to the process by joining fragments and reconstructing objects so that they can be documented. We also have ongoing preservation projects at the museum to make sure that objects are stored properly and stable over time. One example is the use of silica gel, which can help control humidity in storage housings.

Working on site moves at a quick pace, but there’s still time for exploring. One of my favorite near by sites is Midas City, known for its monumental rock carvings. Visiting different sites and museums, such as the Museum of Anatolian Civilizations, helps contextualize my work and adds to the experience. There’s still more to come from this busy season!

The Midas Monument at Midas City.

Two human figurines from Tureng Tepe

Preparations for the opening of our new Middle Eastern Galleries are well underway. Take a peek into either of our lab spaces (both the Artifact Lab and our main lab spaces) and you’ll see a multitude of artifacts being treated for this upcoming exhibition.

I recently treated two ceramic human figurines which will be going into a case with several other figurines from Tureng Tepe, a site in northeastern Iran.

Map of archaeological sites in Iraq and Iran, with a red star next to Tureng Tepe. Base map image credit: University of Chicago.

One is female, and mostly complete, and the other is a male torso.

Like most objects for the Middle Eastern Galleries, both of these objects needed treatment. And they represent two different reasons for treatment, which we commonly seen in our lab.

The female figure had a couple different problems. First, and most obviously, her head was detached.

A detail of 32-41-68, before treatment.

The other problem stemmed from the fact that she had been treated before. In the 1980s, she was desalinated by soaking in water, and consolidated with PVA-AYAF, a polyvinyl acetate resin. Both of these interventions were important for the long-term structural stability of this piece. But the problem related to old treatment was an aesthetic one – there were areas on the body that were very discolored/gray, which made for a splotchy appearance overall. You can see these gray patches in the images above. These gray patches were also very shiny, and were related to a coating that had been applied to the figure at some point – possibly the old PVA consolidant.

Treatment of this figure included removing the darkened coating by swabbing with acetone, and some mechanical removal with bamboo skewers. The head was reattached with Paraloid B-72. There were some areas where the ceramic body was flaking and these areas were consolidated with a dilute solution of Paraloid B-72 in acetone and ethanol.

32-41-68 before (left) and after (right) treatment

In contrast, the male figure had never been treated. When I first laid eyes on him, I thought to myself, “Terrific! This piece looks like it will just involve documentation. It will be in and out of the lab within a day or two.” Well, looks can be deceiving, and I quickly realized that the male figure had a soluble salt problem, related to the burial environment. I actually haven’t discussed soluble salts on this blog before. You can read a nice explanation of soluble salts, how they affect archaeological objects, and what we do about them, in Tessa de Alarcon’s blogpost on the Penn Museum blog.

The most obvious signs of soluble salts were the small flakes of ceramic sitting under the figure in its storage support. A quick spot test for chlorides was positive, so I made the decision to desalinate the figure by immersion in water for several days. After desalination, I readhered the small flakes, and the treatment was complete.

Before (left) and after (right) treatment images of the male figure from the side. Small flakes were reattached in the area indicated by the red arrow.

32-41-62 before (left) and after (right) conservation treatment.

As I mentioned, these artifacts will go into a case with several other human figurines from Tureng Tepe. We have, or will be treating a number of figurines from several different sites for the Middle Eastern Galleries. I am including images of some of these figurines below. Personally, I like the ladies with their hands on their hips.

Human figures. Link to larger images and more information by clicking on their numbers (listed from left to right): 32-41-25, 31-43-450, 43-29-3, 58-4-3, 31-16-733, 31-16-734

A final look at Ptah-Sokar-Osiris

Julia Commander is a third-year graduate student in the Winterthur/University of Delaware Program in Art Conservation. She is currently completing a curriculum internship at the Penn Museum.

When we last checked in with the Ptah-Sokar-Osiris figure, I was working on finding a satisfactory cleaning approach. The figure has a darkened layer over the front surface, which obscures the beautiful patterns, colors, and hieroglyphs. My goal for cleaning was to clarify designs and improve legibility, although the sensitivity of the paint layers has made this an interesting challenge.

After cross-section analysis, I looked into instrumental techniques to better understand the condition issues. One promising technique was gas-chromatography mass-spectrometry (GC-MS) since the darkened layer was potentially a coating material. I took a sample by swabbing the dark layer from the wood substrate. Since only a small amount of material can be gathered this way, I collected several swabs in a glass vial for analysis. I sent this down to Winterthur Museum’s Scientific Research and Analysis Laboratory (SRAL), which has previously collaborated on samples from the Artifact Lab. Dr. Christian Petersen, a GC-MS specialist, sent back my spectra with some interesting results. He described the mixture as “waxy dirt,” which helps to clarify what likely happened to the surface. Wax may have been applied to consolidate the badly flaking paint, and this layer could have trapped dirt over time as the figure rested face-up in storage.

Focusing on the wax component did not immediately produce better cleaning results, and I continued testing gels with variations on solutions, application method, and timing. I eventually tried an application of Pemulen TR-2 gel, a polymeric emulsifier, with a proportion of solvent added. This gel was more effective for lifting the waxy grime and did not require excessive action on the surface. Used along with a silicone solvent barrier layer, I was able to lightly clean without lifting pigments from the surface. While I had some initial ideas about cleaning, this method was something that I only found through the process of trial and error.

L-55-29 detail, cleaning test

Even though I cleaned slowly in very small sections, the actual treatment step took much less time than the research, testing, and planning phases. Take a look at the results below.

L-55-29, before cleaning (left) and after cleaning (right)

Aside from cleaning, a few other steps were taken to stabilize the statue. The headdress, which is constructed from multiple pieces of wood, had a large gap that allowed the pieces to move individually. To add support and decrease movement, removable fills were made from Volara foam and Japanese tissue. These materials were turned into small “pillows” that were then pressure-fit into place.

L-55-29 headdress, shaping and fitting Volara foam fills

The figure, headdress, and base do not fit together in a stable arrangement. Instead of intervening further with the object itself, an exterior mount will be constructed to hold the components in place. This method has worked well with a similar Ptah-Sokar-Osiris figure, which you can see displayed in the Upper Egypt Gallery!

Another Ptah-Sokar-Osiris figure on display in Upper Egypt, showing the back of the figure and the mount holding the three pieces together.

Overall, this project provided quite a few challenges and an opportunity to explore cleaning techniques. Thanks for following along on this experience with Egyptian painted surfaces!

Update on one of the Al-Ubaid Friezes

The treatment of the two Al’Ubaid Friezes has progressed since the last post. This post is going to focus on what we have been doing with the marching bull frieze (B15880). This frieze is made up of shell pieces for the bulls (probably made from large conch shells) on a background of black stone pieces with copper alloy borders at the top and bottom of the frieze.

B15880, frieze of 6 bulls

The archaeologists who excavated these materials in the 1920’s set the mosaic into plaster over a wooden backing. Overtime, this support had started to flex, causing the plaster to separate from the wood. This lead to movement of the mosaic frieze casing pieces to loosen and detach as well as causing breaks in the stone. Over the years detached pieces were re-adhered using a variety of different adhesives depending on when the work was done.

Diagram of B15880 showing the 1920’s backing materials in relation to the copper, shell, and stone materials of the frieze.

Because of these issues the mosaic has now been removed from the 1920’s support. One of the perks of having the pieces free from the support, is that we can see both sides of each piece. While we knew from the X-ray that in antiquity they had been attached to the original support using copper alloy wire twists, we can know see those twists.

Detail of the shell showing the remnants of a copper alloy twist/fastener

Detail of the stone showing the remnants of a copper alloy twist/fastener

Now we are working to stabilize each individual piece. The shell bulls are in very good shape, so that has just been cleaning to remove the plaster, areas of over-paint, and adhesive residue. The stone pieces are, however, in much worse shape. We have been consolidating them to restore the cohesion of the stone, joining broken fragments, and cleaning to reduce plaster and old adhesives.

Image showing the progress on cleaning and stabilizing the mosaic pieces.

The next step will be to adhere the clean and stable pieces to a new backing with new grouting around them to keep them in place. Exactly what materials we will use and how that will be done is something we are still working on, but here you can see some of the test tiles that we are making to help make that decision!

Test tiles with bone beads and different possible grouting materials.

 

Treatment of a Huron cigar case

To prepare this jewel of a cigar case for exhibition, lifting and detaching moose hair and splits in the birch bark had to be stabilized.

Before treatment image showing the cigar case from the side, with arrows indicating lifting and detaching moose hair (red ) and splits in the birch bark (green)

A small piece of twisted Japanese tissue paper used to replace some of the missing threads

 

Some of the lifting moose hair was stabilized with dabs of 5% methyl cellulose. For the lifting moose hair around the edges of the case, much of this damage was exacerbated by the missing brown thread stitches. For these areas, after re-positioning the moose hair, I recreated the missing threads with twisted Japanese tissue paper fibers, toned with acrylic paint.

 

The fibers were adhered in place with Lascaux 498, an acrylic emulsion.

Before (left) and after (right) treatment images, with red arrows indicating the locations of the replacement stitches

Unstable splits in the birch bark were repaired from the interior with Japanese tissue and Lascaux 498. Additional support splints made of twisted Japanese tissue fibers were added to the exterior in one place on the lid.

Before (left) and after (right) treatment images of the lid. The red arrows indicate the location of the split and the repair splints used on the exterior.

The cigar case is now on exhibit in our Native American Voices gallery. I only learned after it was installed that it dates to 1850 – much older than I realized! Its age makes it an even more remarkable piece.

The cigar case on display in the Native American Voices gallery

Moose hair and birch bark

Moose hair and birch bark. Those are 2 materials that we have not written about on this blog before. But now that we are working in the Artifact Lab on objects for all of our upcoming exhibitions and loans, we are seeing a wider variety of artifacts and materials in the lab.

This embroidered birch bark case will be installed in our Native American Voices gallery later this month, so it is in the lab for examination and treatment.

Views of both sides of a small birch bark and moose hair case (45-15-1328) 

The 2-part case (the lid is a separate piece) was purchased by the museum in 1945. It is attributed to being Huron and from Canada.

The case itself is made of birch bark and it is embroidered with moose hair. The intricate details are difficult to appreciate without being able to see them up close. So, let’s take a closer look at the decoration:

Details of the moose hair embroidery, 7.5X magnification

Details of the moose hair embroidery, 20X

The case and lid are edged with bundles of moose hair attached with thread:

Details of the moose hair embroidery, 7.5X magnification

As you can see in the image above, some of the threads attaching the moose hair bundles along the edges are missing, causing hairs to become lost. These areas, as well as splits in the birch bark, will have to be stabilized before this case can go on display.

Check back for post-treatment photos, and visit the museum to see this case on exhibit by the end of May.