The influence of different tempers on the composition of pottery
The modification of the raw clay by the potter to produce a paste suitable for the intended purposes adds a layer of obfuscation to the problem of provenancing the original clay source by chemical fingerprinting. By preparing different pastes from the same commercially available raw clay and their chemical analysis by Instrumental Neutron Activation Analysis, an experiment under controlled conditions (tempers, mixing ratios, firing temperatures and sampling methods) sheds light on the influence of different tempers. The results show that two different sampling procedures (drilling and grinding) have almost no influence on the chemical fingerprint with the exception of the elemental concentrations of As, Zr, and Hf. This may be due to the volatility of the compounds (As) or the presence of zircon crystals (containing Zr and Hf) which are partly lost during drilling. Three different firing temperatures show no significant influence as well. The application of the modified Mahalanobis distance introduced by Beier and Mommsen in 1995 as a statistical filter and the introduction of a ‘dilution factor’ to the raw data show that the influence of quartz-dominated tempers can be filtered out of the data, resolving the underlying chemical fingerprint of the original clay source. At the same time, by mathematically removing the additional spread introduced by dilution, even subtle differences between similar pastes can be resolved by standard multivariate statistical means.
Amphorae from Lyons : Petrographic and chemical arguments
This paper briefly presents a method for the interpretation of quantitative petrographic data and chemical composition data from amphorae found in Lyons with the aim of determining whether or not the amphorae are of local production. We will try to define the exact place of each argument in our reasoning about the attribution of the origin of these ceramics, while insisting on the zones of uncertainty for each method. It is important to emphasize here that in assigning the origin of the Lyons amphorae all the arguments must be used conjointly. The presence of rhyolite in the temper is not enough to determine the Lyons origin of an amphora, and the geochemical arguments are often insufficient to make a decision. It is a reasoned application of petrographic, geochemical and archaeological arguments which enables us to pronounce an attribution.
Microstructural changes during the firing of stoneware floor tiles
Abstract The behaviour of a typical composition of low porosity ceramic tiles during firing was characterized before studying the mechanisms involved in sintering. The main physico-chemical transformations were studied by evaluating changes in porosity, microstructure and mineralogical composition in samples fired at different temperatures.