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Documentation, Technical Analysis and Treatment of a Bitumen Model Boat from Ur Caroline Roberts ([email protected]), Winterthur / University of Delaware Program in Art Conservation presented at the 2010 IIC Istanbul Congress – Conservation and the Eastern Mediterranean DOCUMENTATION TECHNICAL ANALYSIS G as chromatoGraphy was used in con- junction with mass spectroscopy to determine the molecular composition of the bitumen component of the mixture. In addition to straight-chain hydrocarbons the bitumen was found to contain lipid ring structures or ‘biomarkers’, which are left from long deceased plants and ani- mals [5]. These structures are often found in crude oil and petroleum byproducts, and can be used to determine the geo- graphic origins of bitumen resins found in archaeological materials. The primary terpenoid shown here likely originated from long-dead marine organisms. s canninG electron microscopy with en- ergy dispersive x-ray spectroscopy used to analyze inorganic materials extracted from the bitumen mixture revealed the presence of calcium carbonate, gypsum, and possible dolomitic minerals (the pres- ence of the first two minerals was con- firmed with FTIR). Silicon minerals (or sand) were also discovered using SEM- EDS analysis. Backscattered electron images of the various mineral particles were also ob- tained, as well as images of the surface of samples of the bitumen / mineral / plant fiber mixture. These images revealed X -radioGraphy of the boat was car- ried out in order to shed light on how the boat was constructed. Plant fi- bers had been discovered protruding from the boat’s break edges, and x-ray images showed that these fibers had been laid down along the boat’s longitudinal axis. The fibers also appeared to have been laid in with greater abundance at the prow and sides of the boat, perhaps to lend added tensile strength to the material in these areas. Sample fibers were examined us- ing polarized light microscopy and were found to have the characteristics of a na- tive grass or reed. 4. Although the paraffin wax applied by Woolley has helped stabilize the surface of the boat over the years, it does obscure its original appearance. Therefore it was decid- ed that the wax should be reduced, in this case delicately with a scalpel after softening the wax with Stoddard’s solvent. 5. A storage mount was built out of etho- foam and covered with washed Tyvek in or- der to support the detached prow. Additional supports will be strategically placed beneath the prow and stern in order to prevent further stresses from being exerted on the center of the boat. T he bitumen boat belonging to the Uni- versity of Pennsylvania Museum of Archaeology and Anthropology is one of a number that were excavated by famed ar- chaeologist Sir Leonard Woolley, as part of the joint archeological expedition at Ur spon- sored by the University of Pennsylvania and the British Museum. Woolley’s decade-long expedition in the early 20th century uncov- ered vast amounts of information about the ancient civilization of Mesopotamia. Situ- ated in the fertile plains between the Tigris and Euphrates rivers at the heart of modern- day Iraq, ancient Mesopotamia endured for over 7,000 years as an epicenter of culture and power in the Near East [1]. The bitumen boat at the PMAA was giv- en an excavation number (U 8847) sometime between 1926 and 1927 and catalogued at the museum in March 1929. The designation ‘TTG’ or ‘Trial Trench G’ had been assigned to the boat during the expedition. This was one of a series of trenches that were excavat- ed by Woolley within the 1926 and 1927 ex- pedition seasons. The exact location of these trenches is not known, but they are believed to have been cut across the western part of the Royal Cemetery. Woolley didn’t assign a specific grave number to the Penn Museum boat and did not include it in the list of ob- jects in the published catalogue. While the Museum attributes U 8847 to grave PG 587 this is most likely a cataloguing error. Based X-Radiography SEM-EDS with X-ray mapping GC-MS analysis on the location of the trench, the date of the boat is probably between 2500 and 2100 BCE [3]. Woolley asserts that the boats served a religious purpose. Many of the boats were found bearing clay or copper vessels filled with food, perhaps as offerings to deities in the afterlife. Another intriguing theory sug- gests that the boats were designed to lure de- mons away from the body, correlating with the fact that they were often found at some- what of a distance from the rest of the ob- jects in the grave [4]. Their presence is also symbolic of the more secular importance of these boats in a society whose many city states were united by a far-reaching network of rivers and canals [2]. TREATMENT T he boat is made of a mixture of bitumen - a naturally-occurring tar-like material that was also used as a binding agent for an- cient mortars - earth minerals and sand, as well as plant fibers. The surface is now coat- ed with a layer of Paraffin wax, which Wool- ley commonly used to support artifacts dur- ing or after excavation. X-radiograph showing fiber orientation British Museum PG627, also discovered at Ur. Woolley, L. 1934 Before Treatment, University of Pennsylvania Museum of Archaeology and Anthropology # B1737(U8847) Map of ancient Mesopotamia Gas chromatograph showing aliphatic hydrocarbon and lipid components of the bitumen Backscattered electron image of the bitumen mixture X-ray map showing inorganic particle distribution After treatment image of the boat pseudomorphs at the surface that reflect- ed the unique morphologies of the plant fibers, including what appear to be bordered pits. Finally, colored EDS mas were obtained in order to reveal the dis- tribution of the various minerals within the mixture. Above, the color red indi- cates calcium-rich (calcite or gypsum) areas, blue and pink represent silicon and aluminum - rich areas (sand) and yellow and orange represent sodium chloride (salt) - rich areas. The surrounding green represents sulfur, which is a component of the bitumen itself. t he Goal of the technical analysis of this object was to shed light on the original context by confirming the materials used in its fabrication; the results also influenced the protocol for treatment. r ationale: The decision to treat the bi- tumen boat came in consideration of its singularity, as well as its inherent insta- bility. The uniqueness of its materials made developing an appropriate protocol a chal- lenge, therefore conservators at the UPenn Museum adnd the British Museum who have worked on bitumen model boats in the past were consulted. 1. Loose sand that had been poured onto the boat subsequent to its excavation was gathered using a soft brush and vacuum, and bagged according to the location it was col- lected. 2. The boat’s break edges were found to be actively powdering; these were consolidated with a micropipette, a technique developed at the British Museum for the consolidation of friable ceramics, using a 5% solution of B-67 in ligroine, a material chosen for its compatibility with the bitumen. 3. Breaks were repaired with 25% Aquazol 50 in ethanol bulked with alpha cellulose and glass microballons, which was tinted with carbon black pigment. References 1 Roaf, M., Cultural Atlas of Mesopotamia and the Ancient Near East, Andromeda Oxford Lim- ited, Abingdon 1966, 10 - 82. 2 Ibid., 122 3 Zettler, R. University of Pennsylvania Muse- um of Archaeology and Anthropology, personal communication, January 30, 2009. 4 Woolley, L., Ur Excavations Volume II: The Royal Cemetery—a Report on the Predynastic and Sargonid Graves Excavated Between 1926 and 1931, Oxford University Press, London 1934, 145. 5 Mills, J., White, R., The Organic Chemistry of Museum Objects, Butterworth Heinemann, New York 1994. 56-67. Acknowledgements The author would like to thank Senior Scien- tist Jennifer Mass, Associate Professor Joseph N. Weber, Associate Scientist Catherine R. Matsen and W. Christian Petersen for their in- valuable input and assistance in the technical analysis of the boat. I would also like to thank Associate Professor of Anthropology Richard Zettler for his help with the boat’s provenance research. Finally, I would like to thank Bruno Pouliot, Conservator of Objects and Adjunct Assistant Professor for WUDPAC, conserva- tors Lynn Grant and Julia Lawson of the Uni- versity of Pennsylvania Museum of Archaeolo- gy and Anthropology, and conservator Barbara Wills at the British Museum and Kate Wight for their help with this treatment. The micropipette technique: A dilute adhesive so- lution is drawn into a capillary pipette (in this im- age a dropper pipette is being used for the same purpose) and released into the powdering break edges via capillary action. Image courtesy of Sagita Mirjam Sunara
