Summer 2004

Empirical Evidence: Applying Chemistry to Archaeology

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Hanneke Hoekman

Home: Holland, Michigan

Major: Archaeology/Chemistry

I.S. Title: Residue Analysis of Ceramics From Late Byzantine and Mediaeval Contexts at Pella, Jordan

Advisers: Nick Kardulias and Paul Edmiston

Asked to pinpoint the origin of her interest in science, Hanneke Hoekman muses, "Well, I’ve always been, maybe, ornery." In grade school she noticed that no girls played drums in the band, so she decided to be the first. In high school, she took four years of Latin rather than Spanish because "Spanish is very practical, but I thought Latin would be more fun." So it was only natural that her reaction to the preponderance of males in science was, "OK, that’s what I should do then."

It was Hoekman’s Latin teacher who suggested she look at Wooster. The match proved a good one for her wide-ranging interests.

"At one point, I wanted to major in chemistry, physics, geology, and maybe anthropology," she admits. Gradually, Hoekman narrowed her focus to a double major in chemistry and archaeology.

Her academic interests came together in an I.S. that analyzes residues found on ceramics from an archaeological site in the northern Jordan River valley: Pella of the Decapolis.

The Pella site was first excavated in the late 1960s by a team overseen by Robert Smith, a Wooster archaeology professor, and two colleagues from the University of Sydney. Located at the western terminus of the Silk Road and other important trade routes, Pella and the other cities of the Decapolis were centers of trade in the Roman and Byzantine empires.

Archaeological evidence – such as the style and decoration of jars and other vessels found at the site – had long suggested trade connections between Pella and Egypt, Cyprus, North Africa, and Asia Minor. Hoekman proposed using analytical chemistry to determine whether microscopic residues of the vessels’ contents confirmed those trade connections.

The College art museum houses a collection of intact pottery from the Pella site, while the archaeology department keeps a collection of sherds which formed the basis for her project. Hoekman selected 43 sherds from the Byzantine (7th-8th century) and medieval (14th century) periods. She broke a small piece from each sherd, ground it to powder (using a special mill purchased with a Copeland grant), and dissolved the powder in dichloro-methane and methanol. She centrifuged the mixture to separate the ceramic pieces, drew off the remaining liquid, and analyzed it using gas chromatography-mass spectrometry. This method separates and identifies each component of the chemical residues.

It took hours of painstaking lab work and many late nights, particularly after the spectrometer broke down for a critical period in January. Yet Hoekman stayed calm.

"She was very meticulous and completely organized through the whole process," says Paul Edmiston (chemistry), one of her advisers.

Chemical analysis is only half of the story, however.

"There’s a tendency to focus on the technique and extract all the specific data, which is fine, but from the anthropological, archaeological side, I have to get students to raise their heads a bit to look at the big picture," explains Nick Kardulias (archaeology), Hoekman’s other adviser. "What does all this information mean in the context of the social system?"

Hoekman concluded that the chemical evidence upheld the view of Pella as a center of trade with North Africa, Cyprus, and Asia Minor during the Byzantine period. She found evidence of other trade connections with China and Europe by identifying residues of berries from China, which were used to make medicines, and Scots pine from Europe, used in scented oils.

The medieval sherds contained only residues of local goods such as date palm and anise, confirming that Pella never recovered its trade position after an earthquake in 747 AD.

"We know that there were trade contacts that eventually linked the Roman Empire and China," Kardulias says. "The issue is, how do you systematically document that? The kind of things that Hanneke’s doing begin that process of getting us a little bit further along in terms of real empirical evidence."

A successful multidisciplinary I.S. requires "a person like Hanneke, who is really talented and wants to be a couple of standard deviations away from the mainstream, both in terms of what she wants to do here and what she wants to do at the next level of her career," says Edmiston.

Hoekman has begun graduate work in anthropology at Florida State University and plans to stay at the intersection of chemistry and archaeology. The field "could become like radio carbon dating, an innovation that totally changed archaeology and helped establish more accurate chronologies."