Researchers at the Department of Mineralogy and Petrology at the University of the Basque Country (EHU-UPV) studied pottery from the Neolithic to the XVI century, generally those artefacts found in the Basque Country. They focused on archaeological investigation using physical-chemical techniques. These have the twin objectives of obtaining information about the technology used in making pottery as well as obtaining data on the raw material(s) used in the production of the pieces.
     The pieces were first classified into a number of different groups by the archaeologists, according to shape, function, decoration and what could be deduced from observations of cuts in the fragments with a magnifying glass. Subsequently, it was the geologists that had to confirm and determine the characteristics of each group. Geologists first carried out a petrographic study of the pieces, using a petrographic microscope. They looked at thin laminas of the samples and, based on the texture and mineralogical composition of both the clay and the additives, they received a classification.
     Then, a mineralogical investigation was undertaken, using X-ray diffraction. In most cases, from a mineralogical perspective, no information over and above that obtained from the petrographic analysis is obtained. But there is one exception: when the pottery has undergone high temperatures in the firing process, given that certain minerals are destroyed and transformed at these high temperatures. This is the reason, amongst others, why X-ray diffraction is used – to see if these mineral indicators appear. Also, if the firing temperature is the same in all the pottery, this suggests that the firing technology was sufficiently developed and controlled.
     Neolithic individuals knew perfectly well what had to be mixed with clay in order to change the physical-chemical properties of the original material. The oldest data from the Mendandia (Saseta, Treviño) site shows that, for example, what was mixed with the clay depended on the final use of the pottery item.
     In the end, the researchers interpreted the treatment of the clay and the aim of such treatment. For example, additives are mixed with the clay to give the latter consistency; if carbonates are added it is because they wanted to use the pottery for cooking.
     Finally, a chemical analysis of the items were carried out, either to pigeonhole the groups or to form new groups. This new technique provides approximate information about the geological material of the area that was the source of this clay; i.e. if the clay is near to or distant from the site, etc. To this end, it is useful to know the geological environment of the site. In any case, the aim is not to exactly delimit the source area of this clay, but simply to mark out an environment. It is believed that some of the groups of remains studied originate from areas around Aquitania and Bidasoa. Certain specific minerals have also been found that are laying down specific geological procedures. Ophites, for example, are very characteristic in all pottery finds in the Pamplona basin.

Source: Basque Research (6 July 2006)