By Katherine Eremin and Marc Walton
In recent years, archaeological research has become a rich, multidisciplinary field that relies on excavation by archaeologists, documentation by art historians, and analysis by physical scientists to tackle the complex process of untangling culture. This collaborative approach to research was certainly not the norm in the early twentieth century, when modern archaeological practices were being established. In those early excavations, more often than not, discovery of small finds such as glass, ornamental metals, and stone objects was of far less interest than the recovery of inscriptions and the uncovering of architecture.
Such was the case with the mound of Yorgan Tepe in present-day Iraq. Excavated by Harvard University between 1925 and 1931, it yielded the late Bronze Age city of Nuzi (fifteenth to fourteenth century BCE). Archaeologists carefully recorded the city's temple and palace complexes as well as scores of cuneiform tablets. However, the myriad small finds of ceramics, stone, metal, and glass were at times only briefly documented in excavation reports.
In 2008 a collaborative project was conceived to reexamine these objects, now housed at Harvard's Semitic Museum, using contemporary archaeological theories and analytical approaches. While all material culture from Nuzi is being investigated under the scope of the project, the glass finds are the emphasis of the initial study. This first in-depth investigation of the glass offered an unparalleled opportunity to increase knowledge and understanding of trade, commerce, and technology of this material in late Bronze Age Mesopotamia and to compare this information with neighboring areas, such as Eighteenth Dynasty Egypt.
STUDYING LATE BRONZE AGE GLASS
Late Bronze Age glasses were prestige materials similar in value to semiprecious stones such as lapis lazuli and turquoise. However, unlike gemstones, glass was a human-made material produced by tightly administered royal monopolies. By following the extent of glass exchange among cultures in the Bronze Age Mediterranean, the mechanisms of its trade, and the means by which its technology was transferred from one location to another, researchers could provide a window into how these monopolies functioned.
In the past decade, the study of glass from this period has been a popular subject for investigation, resulting in an improved understanding of where primary glass-making workshops may have been located in both Egypt and Mesopotamia. This research has been based on both chemical evidence and archaeological excavation.
A significant development in the study of late Bronze Age glass came in 2007, when a way to discriminate chemically between the main sources of glass from this period was discovered by Andrew Shortland of Cranfield University in Britain and Katherine Eremin of Harvard Art Museum. Using inductively coupled plasma mass spectrometry (ICPMS), Shortland and Eremin established that there are consistent differences in the trace element compositions of Egyptian and Mesopotamian glasses (many of these coming from Nuzi), related to their different materials of manufacture. Shortland and Eremin hoped to expand on their initial findings by undertaking a more comprehensive examination of all the glass finds at Nuzi.
Archaeological research has become so specialized that not all questions can be answered by a single institution. In fact, the key to success in the analysis of archaeological objects is to build a research team that balances in-depth knowledge of the period and material being analyzed with appropriate analytical expertise. This type of multi-institutional and multidisciplinary collaborative approach is now becoming commonplace in archaeological research. It is therefore not surprising that at the start of the Nuzi project, it was recognized that a major scientific reinterpretation of the glass finds would not be possible without active and dynamic interaction among a number of institutions and individuals who would be able to bring different analytical techniques and interpretative ideas to the table.
The international group assembled for the Nuzi project included the Semitic Museum; Cranfield University; Harvard Art Museum; the Catholic University of Leuven in Belgium, which has the premier laboratory for determining radiogenic isotope content in glass; and the Getty Conservation Institute, which owns one of the only laser ablation inductively coupled plasma mass spectrometers (LA-ICPMS) dedicated solely to trace element analysis of museum-based objects.
COLLABORATIVE WORK UNDERTAKEN
To date, the comprehensive analysis of the Nuzi glass materials has revealed that there was no significant trade in glass between Egypt and Nuzi. In fact, almost all the glasses found in Egypt have been shown to have an "Egyptian" trace element composition, and likewise, all the glasses from Mesopotamia (Nuzi and other sites) have a unique "Mesopotamian" signature. This finding, based on analysis at Cranfield University and at the GCI, was also corroborated by isotopic data collected at the Catholic University of Leuven. These findings suggest that although the elite may have given one another small gifts of glass, these two major late Bronze Age cultures were not engaged in robust trade. It is more likely that local demand for glass was satisfied by local production. It is therefore interesting that Mycenaean (late Bronze Age Greece) beads from the J. Paul Getty Museum, also analyzed at the GCI as part of this study, were found to have both Egyptian and Mesopotamian signatures. These analyses suggest that there was an active glass trade between Mycenaean Greece and both Egypt and Mesopotamia.
The best-preserved and most colorful beads from Nuzi are on display at the Semitic Museum and could not be sampled using mechanical methods (e.g., by scalpel or saw). In 2008 some of these beads were taken to the GCI for in situ analysis by laser ablation ICPMS. Laser ablation sampling was deemed the least-invasive quantitative measurement technique, since it produces only a discreet 60 µm wide crater that is a mere 50–100 µm deep in the object—and is therefore invisible to the naked eye. Such minimal removal of material was necessary for these glass beads, given their small size, rarity, and use in displays.
Analysis showed that this well-preserved glass was extremely unusual for the late Bronze Age. All of the glasses exhibited higher aluminum levels than normally seen in glasses from this period and also showed the presence of lead-tin yellow colorant that was not used in glass until the Roman period (second to third centuries CE). Isotopic data from a single multicolored bead also confirmed that the strontium and neodymium isotopes did not match other late Bronze Age Near Eastern glasses. Based on the chemical comparison of these glasses, it was found that these beads more closely resembled Byzantine glass than anything from the Bronze Age. Subsequent formal analysis of the beads showed that they indeed matched shapes, colors, and decoration of other beads dating to the Byzantine/Sassanian periods in Iraq (third to fourth centuries CE). We now believe that many of the highly colored glasses in the Nuzi collection are intrusive material from later occupation of the archaeological site and hence cannot provide any information about the Bronze Age culture of interest. They do, however, highlight the dangers of working with collections excavated before modern excavation practices were fully established, as well as the need for careful examination of all objects and records.
WHAT WAS GAINED
Through this collaboration, we have established fundamental analytical evidence for the trade of glass in the late Bronze Age Mediterranean. This would not have been possible without the initial efforts by Shortland and Eremin to establish the compositional fingerprints of the glass and then to apply those fingerprints to the study of a wider body of material. However, a key ingredient to the success of the project has been the diversity of knowledge—in chemistry, geology, and archaeology—brought together in the Nuzi team. This wide-ranging knowledge has resulted in new insights into this late Bronze Age past.
Katherine Eremin is a conservation scientist at the Harvard Art Museum. Marc Walton is an associate scientist at the GCI.