The Desalination Station II: The Salty Pot Field Diaries

by Tessa de Alarcon

So I have written before about desalination to stabilize ceramics with soluble salts, but this time I’m going out into the world, and setting up a desalination station for the Naxcivan Archaeological Project in Azerbaijan.

I had been given a heads up from colleagues Brittany Dolph Dinneen (the previous conservator on site) and Jennifer Swerida (project registrar), that soluble salts may be an issue with the ceramics from the project’s excavations. Salts can be tricky to identify with freshly excavated material, as the ceramic vessels won’t have visible issues until a while after their excavation; once the salts from the burial environment have had time to go through a few cycles of crystallization and deliquescence.

Before treatment image of QQ.15.155: the white haze is from soluble salts

Here at on the Naxcivan Archaeological project, the salts are mostly manifesting as a white haze over the surface of ceramics.

Detail of QQ-15-193 showing small salt crystals, rather than just hazing, on the surface.

A few are also showing clear crystallization, but the hazing has been the more frequent symptom of the salt problem, especially as this hazing was not observed when they were first excavated.

Detail of QQ-15-155: the poultice in place.

To confirm that what we were seeing was in fact soluble salts, I poultice the surface.

Detail of QQ-15-155: after the poultice was removed

Once the cotton poultice was dry, I removed it from the surface, re-wet and checked the conductivity, and tested it for nitrates and chlorides with test strips (there are lots of other types of soluble salts, but these are two common ones that are easy to test for). The results were positive, and as you can see the poultice also removed the white haze clearly showing how soluble these salts are.

Here Calypso Owen and I are filtering water from the sink with a deionizing column to get salt free water.

The next step is getting the water, and while we used to use a similar system at the museum to make deionized water, the scenery is pretty different.

Salty ceramics soaking in deionized water: the tags outside the buckets are being used to help track the objects during treatment.

The pot then soaked for a day, while I checked the conductivity until it reached the end point of the desalination process.

Desalinated ceramics after they are removed from the water and are now drying: again the tags are moving with the objects so we can track them.

Once it was removed from the water I rinsed it with fresh clean water, blotted it dry, then left it to air dry.

QQ.15.155 after treatment: white haze free!

Finally, here is the bowl after desalination. As you can see it is now white haze free. Most importantly, it can now be handed over to the Naxcivan Museum with no risk of damage from ongoing salt cycles.

View from the current excavation: Azerbaijan is beautiful

As a final note, it has not been all work, I did get to hike up to the current excavation and I wanted to end on this photo taken from the site, as Azerbaijan is stunning, and I can’t resist the opportunity to share.

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