## 3 Results and Discussion
### The Terracotta Body  
The ceramic mixture shows the same mineralogical and chemical characteristics in all the samples. In Figure 12 the SEM microphotograph of a section of terracotta body is reported. A groundmass of glass-phases and relict of clay minerals are visible associated with silicate mineralogical phases. From a mineralogical point of view, the XRPD analysis showed the presence of gehlenite (Ca\({}_{2}\)Al\({}_{2}\)SiO\({}_{7}\)), wollastonite (CaSiO\({}_{3}\)), quartz (SiO\({}_{2}\)), calcite (CaCO\({}_{3}\)), fassaite-diopside (CaMgSi\({}_{2}\)O\({}_{6}\)--(Ca, Na) (Mg, Fe\({}^{2+}\), Al, Fe\({}^{3+}\), Ti) [(Si,Al)\({}_{2}\)O\({}_{6}\)]) type and traces of feldspar (K feldspar--KAlSi\({}_{3}\)O\({}_{8}\)) and plagioclase (NaAlSi\({}_{3}\)O\({}_{8}\)--CaAl\({}_{2}\)Si\({}_{2}\)O\({}_{8}\)) (Figure 13). The presence of calcite (even if in small amounts) has been detected in all samples and the remarkable presence of gehlenite together with calcite. The presence of gehlenite indicates firing temperatures more than 850 \({}^{\circ}\)C [5]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **wt\% Na\({}_{2}\)O** & **wt\% MgO** & **wt\% Al\({}_{2}\)O\({}_{3}\)** & **wt\% SiO\({}_{2}\)** & **wt\% K\({}_{2}\)O** & **wt\% CaO** & **wt\% PbO** \\ \hline F01 & 1.91 & - & 1.51 & 33.75 & 1.86 & 2.05 & 58.91 \\ F05 fr2 & - & - & 1.35 & 38.33 & - & 22.56 & 37.82 \\ F02 & - & - & 0.83 & 25.01 & - & 0.77 & 73.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mean values of oxides concentrations (wt%) measured by SEM–EDS for the groups identified on the basis of the glaze and the interface texture. We reported an average value of the composition obtained from 5 EDS areas for each glaze. The analysed area is 30 \(\times\) 30 \(\upmu\)m.  
Figure 12: SEM-BSE photomicrograph of terracotta body (F_02). Major, minor and trace element concentrations for the fragments sampled to investigate the terracotta composition, have been measured by ICP-MS and are reported in Table 4.  
The chemical and mineralogical composition gives an indication of the nature of the raw material and the technological characteristics with which the ceramic body was manufactured. The main pyrometamorphic phases found (wollastonite, gehlenite and a \"ceramic pyroxene\" probably fassaite-diopside type slightly Fe-, Mg- and Ca-rich) are clearly related to Ca-rich ceramic pastes [38]. The chemical analysis of the ceramic body confirms that the resource was a calcareous clay, with a lime content around 30-35 wt% CaO. There are several advantages of using calcareous clays as has been highlighted previously [39, 40, 41, 42] and surely known very well by the craftsmen: excellent porosity in the obtained ceramic piece, strength and weather resistance and resistance to cracking after lead glaze coating [41]. Visually, the colour of the clay body is generally a light yellowish buff, even if the total iron oxide contents were in the range of 3.57-3.92 wt% Fe\({}_{2}\)O\({}_{3}\). No red colour appeared, since, instead of forming hematite, the iron oxides were incorporated into calcium iron silicates [40]. In Table 5, the estimation of the firing temperature obtained by the method developed by the CHART-group at the University of South Denmark [30], which relies on measuring the magnetic susceptibility on a stepwise refi