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.

Image_01 march

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).

Using UV light to examine ancient paint

BY MADELEINE NEIMAN, 2014–2015 Samuel H. Kress Conservation Fellow at the Kelsey Museum. During her time here, Madeleine’s work will focus on the technical analysis and treatment of objects from Seleucia on the Tigris, a site approximately 18 miles south of modern-day Baghdad, Iraq.

One of my major projects here at the Kelsey is conducting a survey of artifacts from the Seleucia collection. The goal of this work is to answer three questions:

  • What are the artifacts made of and how are they made?
  • What is the condition of the object? More simply, is there any evidence of damage or deterioration (e.g., breaks, cracks, discoloration) present?
  • Have the objects been modified (e.g., repaired or reused) in any way by modern or ancient people?

Conservators utilize a number of tools to help us answer these questions. Today I thought I would share with you a bit about one of our most commonly employed techniques — examination under ultraviolet light.

Light is a form of electromagnetic radiation and exits as part of a large electromagnetic spectrum. Ultraviolet radiation, often called UV light, refers to that area just below what is visible to the human eye. While we can’t see UV light, when it illuminates the surface of an artifact, certain types of materials, including some dyes, minerals, and resins commonly found on archaeological objects, fluoresce. These materials glow different colors!

Let’s look at an example.

Among the over 13,000 objects in the Seleucia collection are a group of bone figurines.   Several of these are decorated with a reddish-pink paint that displays a unique orangey-pink fluorescence.

Images of bone figurine (16187) with pink paint captured under visible (left) and UV (right) illumination.
Images of bone figurine (KM 16187) with pink paint captured under visible (left) and UV (right) illumination.

In antiquity, people created paints using mineral pigments as well as organic colorants found in plants and animals. Among the most common sources of red were the pigments hematite (iron oxide), cinnabar (mercury sulfide), and red lead as well as the dyes kermes (from the Kermes vermilio insect) and madder (from the plant Rubia tinctorium).  When viewed in visible light all five appear red. However, when examined under UV light, one stands out: madder. Madder contains four principal colorants: alizarin (red), purpurin (red), pseudopurprin (red) and xanthine (yellow). The purpurin and pseudopurpurin glow a bright orangey-pink when exposed to UV light, making it easy to distinguish.

By examining the figurines under UV light we can tell that an ancient artist used madder to decorate these figurines!