Artifact investigation

CAROLINE ROBERTS, Conservator

I love a good mystery, and nothing (save a really good crime novel) is better than an artifact mystery. I love the thrill of investigating an object, identifying its agents of deterioration, and nabbing those culprits one by one. I also really enjoy teaching new conservators how to use investigative tools to make their own observations. I recently spent a day looking at an object with Ellen Seidell, a U of M junior who is interning in our lab. The ceramic bowl — excavated at Karanis in 1929 — was covered with feathery white crystals, as well as a drippy, peeling surface coating. I had my suspicions as to what these were, but wanted Ellen to learn for herself how to identify unknown materials.

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Left: Ceramic bowl before treatment. Right: bowl under longwave ultraviolet light.

To do this, we examined the bowl under longwave ultraviolet light. This is a useful tool not only for crime-scene investigation, but also for identifying varnishes and coatings. Ellen and I could immediately see a bright yellow luminescence on the surface. We then performed a chemical test to determine that the coating was cellulose nitrate — a material used to treat newly excavated artifacts in the 1920s and ’30s. Finally, we determined that the white crystals were salts. Water-soluble salts like these can be absorbed into artifacts during burial. Fluctuations in humidity can cause salts to crystallize and re-crystallize inside the object, which can cause damage to artifact surfaces.

So what did we do with this evidence? First, we decided to remove the salts. I felt that this would be a good experience for Ellen, since not all salty bowls have the advantage of being in a climate-controlled museum, and since monitored desalination is an important conservation skill. Next we addressed the coating, whose identity allowed us to choose an appropriate solvent for its removal — which Ellen did herself. The treatment is complete, bringing the case of the salty, peeling bowl to a close (for now).

Documenting demons in the infrared

BY CAROLINE ROBERTS, Conservator, Kelsey Museum of Archaeology

This demon bowl, which was excavated by the University of Michigan in the 1930s, now resides in the Kelsey Museum. It comes from the ancient city of Seleucia, which is located not far from Baghdad along the Tigris River. If you look closely at the bowl, you can see that the inside is covered in rows of what looks like text, as well as four line-drawn figures. These are demons (hence the title “demon bowl”) and they reveal the function of the bowl: to trap demons.

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Two views of the “demon bowl” (KM 1931.455). On the left, a visible-light image; on the right, an infrared reflected image. Photos by Aaron Steele.

Unfortunately, the bowl has a dark gypsum crust which obscures these super cool and creepy demons. Fortunately, we know there are ways to see though the crust, and Madeleine Neiman, who worked as a Samuel H. Kress Conservation Fellow in the Kelsey conservation lab during the 2014–15 academic year, spearheaded a project to investigate the bowl. This included looking at the bowl with infrared reflected (IRR) imaging.

IRR is a technique used by conservators to reveal difficult-to-read painted inscriptions, or drawings under paint layers. The Detroit Institute of Arts Conservation Department has its very own Goodrich SWIR infrared camera. The SWIR’s capture range surpasses that of the modified DSLR camera we use for IRR at the Kelsey, and Madeleine found that infrared light at this higher range could pass through the bowl’s darkened crust. So we packed up the bowl and drove to Detroit to see what we could see.

The Goodrich camera was able to reveal the bowl’s inscription, thanks to the IR transparency of the gypsum crust and the heavy IR absorption of the inscription. The result is a higher visual contrast between the inscription and the surrounding ceramic, making it easier to read. Okay, actually “reading” it is hard to do, given that the inscription is not real script! But you get the picture. What I found fascinating is the high level of detail revealed in the images of demons on the bowl, including flames, raised arms, and scary faces. These unique characteristics are all the more visible thanks to the power of infrared light.

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Detail of a demon in the infrared reflected image. Photo by Aaron Steele.

I’d like to thank our DIA colleagues Aaron Steele and Aaron Burgess for taking the time to capture these images, as well as Madeleine Neiman for helping us uncover the demons who have been hiding underneath that dark (and scary) crust!