Internet Archaeology. 9. Affonso. Discussion

5.0 Discussion

Petrographical and chemical analysis indicated that figurines of Nevali Çori were produced with local raw materials. Not only are they mineralogically similar (Figures 4 and 7; 5 and 9), but also they are similar in the main chemical composition (Figure 12) and trace element patterns (Figure 13), attesting that all materials used occur at the vicinity of the site. Microscopic comparison of the figurines and the clay raw materials from the surrounding area of the site indicates, however, that the artefacts contain higher amounts of subangular grains of silicates as inclusions than the natural materials. At present there is virtually no alluvial sand in the vicinity of the site. Thus, it must be concluded that either the temper was specially prepared by crushing stones or that small occurrences of alluvial sand along the Kantara or the Euphrates valley, now inaccessible because of the inundation, were used.

Thermoluminescence glow curves indicate an average firing temperature above 450°C for all objects (Dr I. Wagner, Archaeometrie Gruppe der Akademie der Wissenschaft, University of Heidelberg). Petrographic and mineralogical comparisons of artifacts and samples from firing experiments made in the laboratory suggest a minimum firing temperature of 600°C. Practically all the artefacts show brown-coloured oxyhornblende, instead of the green-coloured ones, that typically occur in the natural sediments of the region. Firing experiments indicate that hornblende begins to alter into oxyhornblende at temperatures above 600°C for the local materials (Figure 14).

Other observations suggest that the maximum firing temperatures did not exceed 700°C:

In the soft marls, the calcite began to decompose at about 600°C, but samples fired over 650°C subsequently disintegrated owing to the recarbonation of burnt lime, suggesting that figurines fired over this temperature could not have survived.
Illite, starts to break down above 650°-700°C, but was identified in practically all of the figurines of calcareous clay and soft marls examined.
Weathering soils show burnt lime when fired over 700°C and well-developed glassy phases over 750°C. As we often observe incipient decomposition of shells but no glassy phases at all in the analysed samples, we must conclude that the firing temperature may have lain between 650°-700°C for figurines made of this material.