The combined use of petrographic, chemical and physical techniques to define the technological features of Iberian ceramics from the Canto Tortoso area (Granada, Spain)

Thirty-two ceramic fragments dating from the Early Iberian Age were collected in Canto Tortoso, an archaeological site located about 100 km from the city of Granada (Spain). The site is on a hill bordered by two rivers, the Fardes and the Guadiana Menor. The ceramics are divided equally into amphorae and vessels and half of them have black cores. The samples are rich in SiO2 and Al2O3, with varying amounts of CaO, Fe2O3, MgO and K2O. The most common mineral is quartz and almost all the samples have muscovite-type phyllosilicates. Calcite appears as small grains dispersed in the matrix and sometimes also of secondary origin covering the surface of samples or filling the pores. One ceramic was richer in calcite grains than quartz. An incipient decomposition of this carbonate is detected even at low firing temperatures. Samples fired at high temperatures are characterised by the presence of mullite or gehlenite and/or diopside phases. These silicates are also accompanied by a vitreous phase that increases the interlocking between the particles and changes the morphology of the pores from angular to round. The precipitation of phases of secondary origin on the surface of the ceramics may have minimised the chromatic differences between Ca-rich and Ca-poor samples. The combined use of chemical, petrographic and physical techniques allowed us to estimate the firing temperature of the ceramic samples (most samples were well-fired) and to discover the provenance of the raw material (a clayey material found near a kiln located just 3 km away from the settlement has a mineralogical composition compatible with that of the ceramics).