Non-destructive Material Profiling of Clay Tablets

Thermal Stability of Mineral Constituents and Conservation History

Individual Research Project

Cuneiform clay tablets are among the earliest written artefact in human history. For thousands of years, these fragile objects have preserved historical data on the languages, societies, literatures, religions, and economics of ancient Western Asia. Yet the very material that carries this knowledge is vulnerable. After excavation, and in a few cases before, many tablets have been subjected to thermal treatments in an attempt to stabilise their surfaces and protect the written signs. However, heating may sometimes cause irreversible damage. Yet, better ways of preserving clay tablets remain understudied, and modern conservation science is reluctant to expose ancient artefacts to irreversible treatments that transform their chemical structure.

Thus, understanding the temperature-induced structural and chemical transformations in the minerals composing the clay tablets is vital for designing safe conservation strategies and for interpreting the treatment history of artefacts whose firing conditions are unknown.

Our project gains deeper insights into thermally activated processes in clays and clay-surface weathering via in situ temperature-dependent Raman spectroscopy and complementary thermogravimetric analysis as well as ex situ x-ray diffraction (XRD) and X-ray computed tomography (XCT) using ENCI, in order to potentially establish a non-invasive and non-destructive method for determining the firing history and the initial mineral and chemical composition of fired and unfired clay tablets.

Raman mapping is applied to annealed clay objects to evaluate whether one can distinguish between unfired and fired clay tablets, deliberately fired in antiquity and in modern times. Test clay objects are analysed before and after annealing by XCT using ENCI to access the structural heterogeneity and probe the thermally-induced changes in the material density of clay tablets, which could potentially link density changes with the phase transitions on the atomic-scale. Raman mapping is applied to clay objects before and after they are being analysed with ENCI, to check, on the atomic-scale level, for undesired side effects induced by XCT. Salinised dummy clay objects are subjected to Raman mapping to check whether the cuneiform signs written in-lab, prior to the artificial salination, can be visualised via the Raman-signal ratio between the clay and salt.

By linking mineralogy, archaeology, and conservation science, we aim to provide new tools for profiling clay tablets in a non-invasive and non-destructive way. The expected results support provenance studies, improve conservation protocols, and contribute to the long-term preservation of some of the world’s earliest written artefacts. More broadly, our results will demonstrate how minerals record environmental and thermal histories via the corresponding structural and crystallochemical changes, allowing researchers to read information stored not only in texts, but also in the material structure of the writing support.