The Effect of Purification and Firing of Clays on Trace Element Provenance Studies

Abstract

The effect of purifying, mixing and firing of clays on trace element concentration was systematically investigated using instrumental neutron activation analysis. Eight different clays from two sites in Crete were used together with sherds found around several kilns near the sites. Trace element analysis showed that the extent to which the concentration changes after purification and firing depends on the initial particle size and chemistry of the clay. The calcite concentration plays an essential role in this. An application is made using roof tiles found at the excavation of the ancient city of Pella in Macedonia.

Alteration and Contamination of Archaeological Ceramics: The Perturbation Problem

“…This process, which is not a perturbation operation as defined in this paper, can actually be modelled as a perturbation induced by firing temperature during the transformation process from paste to fabric. Therefore, the logratio transformation also allows us to control the effect of this paste-to-fabric change, and the diversification of compositions with the apparent dilution effect for the determined concentrations (Kilikoglou et al, 1988). …”

“…In the second stage, there exists the variability introduced by the potter during the preparation of one or more pastes, depending on the particular use the pottery is to be put to (Steponaitis, 1984;Cuomo di Caprio, 1985;Arnold, 1992). Finally, the paste can be diversified during firing, resulting in different transformations which affect mineralogy (Maggetti, 1981), chemical composition (Widemann et al, 1975;Kilikoglou et al, 1988), as well as physical properties including microstructure and colour (Picon, 1973;Tite & Maniatis, 1975;Dufournier, 1982;Béarat et al, 1989). As a result of these changes a paste may then result in the production of one or more fabrics (adapted from Whitbread, 1989, 127).…”

El análisis composicional en el estudio de la producción y distribución de la cerámica prehispánica

“…En cuanto a la estructura y composición química, la variación es inevitable, pues las altas temperaturas producen cambios mineralógicos y microestructurales en la matriz de arcilla de la pasta. Aún así, los experimentos indican que la mayoría de elementos químicos no se volatilizan significativamente durante la cocción, con la posible excepción de arsénico, azufre, bromo y cloro, cuyo punto de ebullición es relativamente bajo (Rye & Duerden, 1982;Kilikoglou et al, 1988;Storey, 1988;Cogswell et al, 1996;Schwedt et al, 2004). Los cambios ocasionados por el impacto térmico generalmente no afectan a la mayoría de las inclusiones minerales en la pasta, por lo que su identificación por el microscopio petrográfico resulta confiable.…”

Standardisation of elemental analytical techniques applied to provenance studies of archaeological ceramics: an inter laboratory calibration studyElectronic supplementary information (ESI) available: five tabular appendices giving element concentrations measured in reference materials. See http://www.rsc.org/suppdata/an/b1/b109603f/

“…However, pottery is preferred over clay because many factors (refining of the raw materials, mixing, tempering etc.) complicate the direct comparison between the composition of the raw material and that of pottery [6,7,8].…”