Getting to Know a Pot -- Microscopically
Ian Whitbread carefully moved the glass slide under his microscope to see the particles of an ancient ceramic pot at another angle.
Before long he looked up at the students gathered round and explained that this particular pot, created around 2000 BC, had been molded by hand rather than thrown on a potter's wheel, and was made of a mixture of clays that included a few minuscule fossils.
He could tell all that and more from a section of the vessel only about 30 micrometers thick-or about half the width of a human hair.
Dr. Whitbread is one of several researchers at the Center for Materials Research in Archaeology and Ethnology who is using scientific techniques to study archaeological materials. Such techniques, explained Dr. Whitbread, are valuable tools in understanding these materials and the societies they came from.
Nevertheless, he said, "while the application of scientific methods has become more or less accepted, only a fraction of the archaeological community really gets involved in it."
As a result, one of the purposes of the Center is to "teach students about scientific analysis so when they become professional archaeologists they carry some of this interest with them."
The study of ancient ceramics at the Center -- Dr. Whitbread specializes in those from Greece, Professor Dorothy Hosler those from Ecuador, and postdoctoral associate Maria Masucci those from Ecuador and Portugal -- focuses on their geological composition. In contrast, most other archaeologists date and describe ceramics by their original size, shape and applied decoration. But such an analysis tells little about how a pot was made, or what it was made from-information that can tell a great deal about the society the pot was created in.
For example, Dr. Whitbread said, geological analyses of ceramic shards from Lerna, a middle Bronze age site in Greece, showed that the settlement once imported a great deal of goods from the island of Aegina. How do we know? Many of the ceramic shards found at Lerna contain volcanic rock peculiar to Aegina.
Similarly, how a ceramic vessel was made can clear up other questions. Suppose a particular ceramic is made of a clay that could have come from site A, B or C. Where did it originate? If archaeologists know how the vessel was made, and only people in site C made their vessels this way, the mystery is solved. "So we compare geological and human factors to tell where a pot originated," Dr. Whitbread said.
To identify the composition of a particular ceramic and how it was made, scientists at the Center first grind down a small shard of the vessel until it is thin enough for the rocks and minerals to become transparent (about 30 micrometers). Grinding the piece in itself is almost an art form, as a second or two can mean the difference between a perfect sample and a small pile of powder.
Dr. Whitbread notes that the shards analyzed this way are not one-of-a-kind specimens or usually of museum display quality. Rather, he said, they were once utilitarian vessels, like our coffee mugs or Corelle plates, and survive today in the tens of thousands.
Once researchers have prepared a thin section of material, they can decide on its geological makeup: under a microscope they compare the individual grains to those of known rocks and minerals. (The Center maintains a reference collection of geological materials.)
Other observations can lend clues to how the clay was prepared or the vessel was made. For example, said Dr. Whitbread, "streaks in the material could indicate that the pot was made of a mixture of clays."
In addition, the orientation of individual particles can tell whether a pot was made by hand (such as coil-wrap pots) or thrown on a wheel. A coil-wrap pot, as most children could tell you, is composed of a rolled cylinder of clay. As a result, the clay particles of the material are aligned horizontally. Thrown pots, in contrast, "tend to have particles that are aligned at an angle, because the pot is being drawn up as it is being thrown," Dr. Whitbread said.
The experienced scientist can scrutinize a given ceramic under a microscope and tell fairly quickly how the original pot was made. But how do you describe the microstructure of that pot objectively, for other scientists to use?
In his own research at the Center, Dr. Whitbread is developing a system to do just that. He is using computer image analysis to describe the geological microstructure of amphoras, large two-handled vessels used by the ancient Greeks to hold wine or oil.
The work is important because current descriptions of the microstructure of ancient ceramics are limited and very subjective. For example, scientists may have the geological microstructure of a representative amphora, but that may not match the microstructure of another, unknown amphora-even if it's from the same area and time. Dr. Whitbread is defining the microstructures of a range of amphoras from the same general area and time. Ultimately, he hopes to "chart the boundaries of [amphora] variation, so other people can determine whether their material is within or outside these boundaries."
Finally, the computer will let him objectively describe the microstructure. Specific variables he hopes to define include the alignment and size of particles and the proportion of certain components.
All of these geological techniques, Dr. Whitbread emphasizes, are aids to other, more traditional archaeological methods. In fact, he said, to get the whole picture archaeologists must use all of the techniques available to them-traditional and scientific.
So while some specialists concentrate on cataloguing the decorative ware from a particular archaeological site, others, like Dr. Whitbread, analyze the geological composition of more utilitarian vessels. Together they slowly recreate the stories of societies that existed long ago.
A version of this article appeared in the March 4, 1992 issue of MIT Tech Talk (Volume 36, Number 22).
Written by: Elizabeth A. Thomson, News Office