CAROLINE ROBERTS, Conservator, Kelsey Museum of Archaeology
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.
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 1920’s and 1930’s. 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).