EMF - Abstracts

Rapid XRD Analysis of a Large Set of Archaeological Ceramics: a Pilot Study.

Manolis Pantos et al. (Daresbury Laboratory)

Firing and consequent cooling are two of the most crucial stages in the production of pottery. Firing is the production step that transforms clay into an imperishable product. Because of this importance to the production sequence, scholars interested in ancient pottery technology often study the firing process of archaeological ceramics. The firing technique applied is reflected in several aspects of the pottery. The resulting attributes that were probably of direct concern to the potter and the customers are the colour of the product and its resistance under mechanical or thermal shock. These properties are a direct result of the influence of firing on the mineralogy of the raw materials. During firing the mineralogical composition of the clay changes, thereby altering its physical properties.

The mineralogy of archaeological ceramics is studied by well-established techniques such as polarisation microscopy and X-ray diffraction (XRD), as well as techniques such as Mossbauer and Raman spectroscopy. XRD is the most direct technique for the identification of the mineral composition of ceramics and it can be used to analyse both inclusions and matrix. Its main disadvantage is that data collection can be quite time-consuming, each dataset requiring several hours. It is mainly for this reason that XRD analysis is usually applied only to a limited set of samples.

The data collection time can be reduced by orders of magnitude, using synchrotron X-rays and a fast area detector. We were able to collect 2D diffraction patterns of more than 100 samples at station 9.6 of the synchrotron radiation source at Daresbury Laboratory (UK) in less than 24 hours using a CCD detector. Powders scraped from the ceramics were loaded in 0.5mm quartz capillaries. The beam footprint was 200 microns and the exposure times of the order of 3-4 minutes in single bunch mode (~20 less intense than at multibunch mode). An additional advantage of 2D data recording is that an easy distinction can be made between fine-particle phases, such as hercynite in pottery produced under reducing conditions, and overlapping reflections of coarser material such as quartz.

The samples were selected to give a rapid overview of the much larger collection at our disposal. They are representative of different types of ceramic wares from Tell Beydar, a 3rd millennium B.C. site in NE-Syria. The set included soil samples and objects in unbaked clay, as well as standard ware, cooking vessels, and more exclusive wares. We discuss the SR-XRD results and relate them to previously performed SEM-EDX and XRF analyses in order to elucidate the different aspects of pottery production at Tell Beydar, emphasising in particular technology and socio-economy.

Developments in automating the sample handling and data analysis procedures can lead to an order of magnitude improvement in speed of data collection and interpretation, thus making realistic the survey of large volumes of archaeological material, whether ceramic or other powders, and the building of reference databases.