In July 2019, I was invited to give a lesson on “the chemistry of ceramic materials” at the First International School of Sciences Applied to Cultural Heritage (ISSACH) in Egypt. The course, organized by the University of Catania (Italy) in collaboration with Ain Shams University (Egypt), took place at the Coptic Orthodox Cultural Center in Cairo (CCOC). Aimed at university students, restorers and researchers, the course had as its objective multidisciplinary scientific training on the most advanced and current techniques of conservation, diagnostics and restoration of cultural heritage for professionals who work in public and private Egyptian institutions such as museums, archives, libraries, and archaeological sites. While I was preparing my speech, which ranged from ceramic materials to ancient and modern techniques, I tried to unite my two souls as a chemist and a potter, addressing the problems not only from a purely scientific point of view but also from a practical approach for those who experiment with ceramic materials, clays, glazes and firings by getting their hands dirty. The first questions I asked myself was what was the oldest ceramic find ever discovered; the technique used to make it, the function of the artifact, the presence or absence of decorations and the firing process used? To my great surprise, I discovered that they were not functional objects or containers for purely practical use, as believed up to the early 1900s, but objects of ritual use. 

The Dolní Věstonice Site
On July 13, 1925, during an excavation campaign conducted by the Moravian Museum and directed by Professor Karel Absolon in the Paleolithic site of Dolní Věstonice (Czech Republic - see figure 1), a sculpture of just 11.5 cm in height was found among the thousands of fragments and zoomorphic figurines that followed the characteristics of the “steatopygia venus” [1] in features and morphology. These sculptures are the most ancient representations of the female human figure, closely related to fertility rites and the cult of the Mother Goddess and typical of the upper Paleolithic period. Many examples generally made of stone or bone have been found in numerous sites around the world.[2] Unlike equally famous specimens, our small sculpture, known all over the world as the Dolní Věstonice Venus, has a characteristic that makes it extraordinary: it is the oldest known work of terracotta sculpture in the world, and for this reason, it is unique. The dating traces it back to the Gravettian culture of the Upper Paleolithic (27000 - 24000 BC). The discovery of this figurine with numerous others fragments and sculptures in the Paleolithic site of Dolní Věstonice allowed the scientists to backdate the invention of ceramic technology by about 14,000 years as compared to fragments of vases found in the Xianrendong Cave in China.[3].

Materials, Methods and Sequence of Fabrication
Based on the first set of wet chemical analyses on the well-known Dolni Vestonice Venus made in the 1920s, Karel Absolon (1877 - 1960), the most important expert of the Paleolithic sites of Moravia, proposed that the figurine was made of mammoth fat and bone mixed with bone ash and local loess. No alumina or potassium was found; thus, clay was initially excluded as a raw material.[4] Only in 1954 [5], based on a quantitative chemical analysis that demonstrated the presence of alumina, Bohuslav Klima supported the hypothesis that the figurines were made of fired clay, sometimes using the term "terracotta." To confirm this hypothesis, in 1989 Pamela Vandiver [6] and her collaborators published the results of analyses obtained on numerous other samples in the prestigious scientific journal Science, confirming that the starting material for the realization of these extraordinary artifacts was local loess, thanks to the comparison to the microstructural characteristics and the crystalline phases present both in the soil and the figurines. Loess (from the German Löss [lœs]) is a periglacial or aeolian (windborne) sediment, defined as an accumulation of 20% or less of clay and a balance of approximately equal parts sand and silt (with a typical grain size from 20 to 50 micrometers), often loosely cemented by calcium carbonate. It is usually homogeneous and highly porous, and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs. The X-ray Diffraction analysis carried out on 3 samples of local loess and 20 fragments of figurines, confirmed the presence of quartz (SiO2), illite, chlorite, dolomite, and anorthite in similar proportions, in both sample types, except for the more abundant calcite in the loess samples. Apatite, i.e., calcium phosphate Ca5(PO4)3, indicative of bone, was sought but not found.  The chemical-physical analyses of the archaeological finds not only answer questions such as the type of material used and its origin but also questions relating to the technique and the construction sequence of the artifact. A microscopic analysis of porosity (the relationship between the pores and the total volume of the material) has, for example, shown a reduction of about 50% in the sculpture’s pores compared to loess (raw material). This difference is important in understanding the process of forming the figurines, because loess could not have been selected in bulk form and carved to shape (subtractive technique); rather the figurines were formed plastically (additive technique) with wetted loess, which allowed the particles to cohere. Test firing of wetted loess resulted in a hard, durable ceramic, whereas firing unwetted loess resulted in a friable, nondurable mass and confirmed the hypothesis that the figurine was obtained from a mixture of loess and water modeled by hand, with the subsequent additions of the head and limbs having been hand-built separately. The analysis of the surface porosity also highlighted the fine processing of the surface through the use of tools to smooth and seal it. No traces of pigments and decorations were found other than the engraved signs to underline the details.

The firing process 
During the firing process of a material containing clays, silicates, oxides and different kinds of impurities, it is possible to observe a series of irreversible chemical reactions that lead to the disappearance of some crystalline phases and the formation of new phases at characteristic temperatures. The presence and/or absence of these crystalline phases is an excellent indication for determining the range of firing temperatures. In general, the starting material is fired (in this case, the local loess mixed with water) and the XRD analysis (X-ray diffraction) is collected for increasing temperature in steps of 100 °C. The resultant diffractograms obtained are compared to the XRD of the archaeological sample until the firing temperature reached generates the formation of the same crystalline phases present in the artifact under study. From the analysis carried out, it was shown that the temperatures reached during the firing of the artifacts were between 500 °C and 800 °C. Furthermore, the particular composition of the local loess, in which the quantity of clay is relatively low, the presence of phosphorus oxide P2O5 (0.6%) has been shown to have a synergistic effect with the other alkaline oxides present, such as sodium, potassium, iron, calcium and magnesium oxides (Na20, K20, FeO, CaO, and MgO), which act as fluxes and produced a durable, sintered mass. Moreover, two structures, identified as kilns based on the abundance of ceramics present, were found in the archaeological site containing over 2,300 ceramic fragments (figure 3). The first structure was an oval pit of about 130 cm x 40 cm, with a depth of about 40 cm and possessing a raised wall in the shape of a horseshoe; the second, at a distance of about 40 meters from the first, measured 1 meter in diameter by 60 cm in depth and was also partly covered by a loess wall. From the analysis carried out on the materials of the two structures, it was confirmed that the temperatures reached were between 500 °C and 800 °C.

Study of fractures on heat shock findings
As already reported at the beginning of this short article, the Venus was found broken into two large fragments. Of the more than ten thousand artifacts collected, only one figure was found to be intact and very small in size. Such repetitiveness suggested to scholars a closer investigation to see whether the presence of such fractures was attributable to accidental events, atmospheric events, thermal shock due to inexperience in the firing or manufacturing processes, or concealed other causes. From the studies carried out on this type of materials through repeated tests it was possible to exclude as the main causes of the fractures: cracking due to drying shrinkage which is extremely low (less than 2%), mechanical fractures due to percussion which produce smoother fragments not compatible with those of ancient finds, simulations of atmospheric phenomena of freezing and thawing i.e. sudden changes in temperature. The only possible cause is the intentional heat shock to which all the artifacts, which we recall represent animals and gods like our Venus, seem to have been subjected.
Rather than probable inexperience on the part of the person who was in charge of firing the pieces, one must consider the possibility that the goal was not to produce long-lasting pottery but that the heat shock during the firing process was intentional and had sociocultural and ritual significance. The practice of heat shock also seems to be supported by the presence of walls around the firing pit that would act as protection for those who participated in the ritual (see Figure 3). Did the artists who made these small sculptures want to make small idols that would last over time or were they part of a fire-related ritual that had propitiatory or divinatory purposes depending on the breaking of the pieces? Although we will probably never be able to give a definitive answer to this fascinating question, the repetitiveness and spread of the technique across many Moravian sites supports the ritual hypothesis.

The fingerprint on the Venus of Dolni Vestonice
More than 75 years after its discovery, a fingerprint on the left side of the figurine back was analyzed. The dimensions of the fingerprint are 3 × 5 mm and it is possible to recognize seven lines. The structure was identified as a negative of human friction skin based on the minutiae ridge breadth and other markers, and was the subject of a scientific study published in the journal Anthropologie in 2002.[7] The authors argue that the fingerprint is attributable to that of a child between the ages of 7 and 15, difficult to identify with the one who modeled the figurine. I like to imagine that even the Paleolithic children were extremely curious and touched everything as is true today.

Conclusions
As a chemist, ceramic artist and scholar, I am aware that there is still much to understand about our adventure as human species on this Earth. Knowledge is an endless journey that allows us to investigate the world we live in and also ourselves. A purely scientific training cannot exclude a humanistic approach and vice versa, since the two visions are extremely important and complete each other in synergy.

BIBLIOGRAPHY
^[1] venus steatopygies (from the Greek words στέαρ, στέατος, "fat," "adipose," and πυγή, "buttocks," hence "with large buttocks") or callipygies (again from the Greek καλλιπύγος, compound of κάλλος, "beauty," and πυγή, hence "with beautiful buttocks").

^[2] Alan F. Dixson, Barnaby J. Dixson, "Venus Figurines of the European Paleolithic: Symbols of Fertility or Attractiveness?", Journal of Anthropology, vol. 2011, Article ID 569120, 11 pages, 2011. 

^[3] Xiaohong Wu, Chi Zhang, Paul Goldberg, David Cohen, Yan Pan, Trina Arpin, Ofer Bar-Yosef, "Early Pottery at 20,000 Years Ago in Xianrendong Cave, China," Science 29, June 2012, 1696-1700

^[4] Karel Absolon, The Diluvial Anthropomorphic Statuettes and Drawings, Especially the So-Called Venus Statuettes, Discovered in Moravia: A Comparative Study Artibus Asiae, 1949, Vol. 12, No. 3 (1949), pp. 201-220

^[5] Bohuslav Klima, Antiquity 28 (no. 109), 4 (1954);

^[6] PAMELA B. VANDIVER, OLGA SOFFER, BOHUSLAV KLIMA, AND JIRl SVOBODA The Origins of Ceramic Technology at Dolni Vestonice, Czechoslovakia, Science New Series, Vol. 246, No. 4933 (Nov. 24, 1989), pp. 1002-1008 (7 pages) November 24, 1989, Volume 246,' pp. 1002-1008

^[7] KRÁLÍK, MIROSLAV, VLADIMÍR NOVOTNÝ, and MARTIN OLIVA. “FINGERPRINT ON THE VENUS OF DOLNÍ VĚSTONICE I.” Anthropologie (1962-) 40, no. 2 (2002): 107–13.