The basic underlying theory for the strength, toughness and thermal shock resistance of brittle multiphase clay ceramics, together with the measurement procedures to determine these parameters, are ®rst outlined. Published experimental data obtained for test bars containing different types of temper and ®red to a range of temperatures are then compared both with theoretical predictions and between themselves. The results con®rm that to produce pottery with high strength requires high ®ring temperatures and low temper concentrations. Conversely, to produce pottery with high toughness and thermal shock resistance requires low ®ring temperatures and high temper concentrations, with platy or ®brous temper being most effective. There is no convincing published evidence that strength and toughness requirements were a signi®cant factor in determining the technological choices (clay type, temper type and concentration, and ®ring temperature) in the production of pottery used as containers for transport and storage. In contrast, the routine use of high temper concentrations and low ®ring temperatures in the production of cooking pots suggests that the requirement for high thermal shock resistance was a factor that at least in¯uenced technological choice in this case. In addition, there is some evidence that limestone and shell were, on occasions, deliberately chosen as temper in cooking pots. The need to take into account the crucial role that the full range of environmental, technological, economic, social, political and ideological factors have in in¯uencing technological choice is also emphasized. This review highlights the fact that our current understanding of the factors determining strength, toughness and thermal shock resistance of clay ceramics is still far from complete. Further systematic measurements of these parameters, together with the establishment of a systematic database of the range of technological choices associated with the production of cooking pots, are therefore to be encouraged.

The effect of quartz temper on the physical and mechanical properties of clay ceramics and the elucidation of the underlying mechanisms that are responsible for these efsects are presented here. Characteristics studied included bulk density, open and closed porosity, density of impervious portion and fracture morphology. Mechanical behaviour was studied by measuring energy dissipation during fracture, Young's modulus, initial fracture toughness and strength in flexure. The signifcant increase in toughness with quartz volume fraction is explained by the development of a model that accounts for the crack distribution around the grains. The archaeological implications of the work are discussed on the basis of all the parameters that might affect the potter's choices of raw materials.V. Kilikoglou, G. Vekinis, Y. Maniatis and P. M. Day workability, reduces shrinkage, assists in even drying and promotes some mechanical properties at the expense of some others (Rice 1986; Rye 1976). The most common rock tempering materials can be classified in two groups: calcite-based materials that chemically react with the clay minerals during firing and materials that are essentially inert at the usual firing temperatures (quartz, feldspar, etc.). The effects of temper on the performance, including mechanical performance, of ceramics was first studied and discussed in the pioneering work of Shepard (1965). Since then several studies have been reported in the literature. Much attention has been given to the explanation of the beneficial effects of certain tempering materials used in the prehistoric New World, with particular reference to crushed shell in comparison to sand. The main shell-tempered pottery characteristics studied have been thermal shock resistance (Steponaitis 1984;Bronitsky and Hamer 1986), strength (Bronitsky and Hamer 1986;Feathers 1989) and toughness (Feathers and Scott 1989). It has been demonstrated generally, through simulation tests, that shell can produce stronger and tougher ceramics than sand, which was replaced as a temper during the Late Woodland period in eastern North America. The same applies to limestone, although it was not used systematically, compared to grit or grog (Hoard et al. 1995). Besides enhanced mechanical properties, there are further benefits in the use of calcite-based tempers, summarized by Hoard et al. (1995): increase of workability, similar thermal expansivity to clay and a plate-like structure that aids crack propagation arrest, in a similar way to modem fibre-reinforced ceramics. However, calcite can be problematic at high firing temperatures (Maniatis and Tite 1981; Rice 1986) and, therefore, it can only be used as temper at low-firing temperatures, less than c. 700"C, where ceramic bodies remain essentially unvitrified and the maximum strength they develop is, thus, close only to their green strength.On the other hand, there have been many cases of high-fired and quartz-based-tempered pottery. A typical example is that of Punic amphorae transported as containers whose specifica...

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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.

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