## 4 Discussion  
The primary goal of these experiments was to explore whether data on pore systems obtained from 3D image analysis of micro-CT scans could be useful in deducing firing temperatures of ancient and historic ceramics. Firing temperatures indicate technological developments [2], and porosity and the structure of pore systems themselves have implications regarding the use functions of ceramics. None of the current methods for studying firing temperatures of archaeological ceramics are completely satisfactory on their own [38; 66]. The results reported here indicate that micro-CT, in combination with 3D image analysis, has the potential to be a useful addition to the toolkit of archaeotherrometry. In addition to providing data for firing temperature studies, the pore system data can contribute to an understanding of the physical and mechanical properties of ceramics that relate to their use functions [1; 71]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Ceramic**} & **Ratio of \# of Edges/\# of** & **Edge Equivalent** & **Vertex Equivalent** \\  & **Vertices** & **Diameter Mean, \(\mu\)m** & **Diameter Mean, \(\mu\)m** \\ \hline
1 & 4.35 & 127 & 235 \\
2 & 5.10 & 129 & 239 \\
3 & 5.60 & 120 & 232 \\
4 & 5.55 & 119 & 235 \\
5 & 5.15 & 125 & 240 \\
6 & 5.35 & 122 & 232 \\
7 & 6.45 & 155 & 308 \\
8 & 5.75 & 120 & 234 \\
9 & 6.15 & 163 & 324 \\
10 & 6.40 & 146 & 292 \\
11 & 6.50 & **182** & 363 \\
12 & 6.45 & 150 & 302 \\ \hline \hline \end{tabular} The lowest value of the means for each variable is in blue; the highest value is in red. Each value is the mean of 2 for that ceramic type.  
\end{table} 
Table 7: Significant (\(p<0.05\)) pore network variables from Open PNM. Figure 17: The ratio of edges to vertices rises with increased firing temperature. Points are the mean of 2. Initially, all data were collected from both 5 \(\times\) 5 mm (10 \(\upmu\)m spatial resolution) and 10 \(\times\) 10 mm (20 \(\upmu\)m spatial resolution) fields of views. Data from the larger spatial resolution were not as strongly correlated with firing temperatures, indicating that achieving the best spatial resolution of pores as possible, while also imaging a large enough area to be representative of the sherd as a whole, is important for characterizing pores in archaeological materials. It is possible that micro-CT images of larger areas with less spatial resolution would work well for studies of particle distribution and for quantifying aspects of the glaze or slip layers and interaction layers, but that is a subject for future research. Most methods for determining porosity measure only connected pores; in contrast, micro-CT analysis provides a measure of total porosity that includes both connected and isolated unconnected pores. The total volume porosity of shends in this experiment was found to be significant for predicting firing temperature, with lower-fired ceramics generally exhibiting a higher volume fraction of pores than higher-fired ones (Table 2, Figure 5). The lowest fired ceramic has the largest volume percent pores and the two highest-fired ones the lowest, but with variation in the middle of the firing range. This finding corresponds to assumptions made in the archaeological science literature, where a lower volume percentage of pores generally implies higher firing temperatures [1; 18; 28; 36]. As firing temperature increases, pores become fewer in number as vitrification of the body proceeds [32; 39; 40] but the amount of porosity is complicated by many other factors. Some of the production steps that affect porosity include the choice of raw materials and fabrication methods, so it is not surprising to see that for the middle of the firing range here there is no simple linear correspondence of porosity with firing temperature [1]. Firing to too high a temperature for the specific mix of raw materials used creates bloating of pores [35; 72; 73] and would increase porosity, and carefully selecting raw materials such as a potash flux that will promote vitrification will reduce porosity.