## 4 Discussion
This is because the clay minerals become aligned and then during drying and firing, thin, elongated, aligned pores can form throughout the matrix [16; 18] (Figure 18, right). Beyond firing temperature, pore size and shape variables contain information about material properties, product functionality, and ceramic technological developments. For example, cooking wares need thermal shock resistance, so they can be repeatedly heated and cooled without cracking; high porosity made up of mainly large pores contributes to thermal shock resistance by halting crack propagation [32]. Organic additives such as chopped straw, which will char and burn out upon firing, serve well for this purpose. For more homogeneous higher-fired wares, small, rounded pores can interrupt microcracks as they initiate, preventing them from continuing to travel through the material. While non-cooking wares have less need for thermal shock resistance, a glassy body lacking pores can exhibit lower strength [1]. Therefore, it is advantageous for higher-fired ceramics to retain some porosity and for these to be small, rounded pores. Despite the potential importance of such information, methods for quantitatively measuring a range of pore size and shape characteristics in archaeological ceramics have been lacking and most descriptions in the literature are qualitative. Some quantitative work  
Figure 18: Processing and fabrication effects include inhomogeneous distribution of pore sizes and shapes (**left**) from incomplete kneading of the clay; and elongated parallel-aligned pores (**right**) from fabrication methods involving application of pressure. Both views are in transmitted plane polarized light, with pores blue. uses image analysis of thin sections; however, scrolling through the hundreds of slices that make up a 3D micro-CT image makes it obvious that no single 2D slice is likely to be very representative of the actual size and morphology of 3D pores. When 3D shape factors are considered, there are many methods available to subdivide and categorize pore measurements. In our work, ten variables related to pore size and morphology were found to be significantly related to firing temperature. It is known that the size and shape of irregular networks of pores are best described with multiple rather than single measurements and they are best measured in 3D rather than in 2D [75; 82]. Four variables decrease with firing temperature. Unsurprisingly, maximum pore volume is significantly larger for the low-fired ceramics and smaller for the high-fired ones. The maximum pore surface area and standard deviation are also both significantly larger for the lower-fired ceramics. Another variable that decreases with firing temperature is the measure of pore elongation (minimum orthogonal Feret diameter/maximum Feret diameter). This trend corresponds to the shift from more elongated pores to rounder ones resulting from a combination of the use of finer, more processed materials for the higher-fired ceramics and vitrification of the ceramic bodies producing new round pores as gases are released. The other six variables, indicating shape factors, increase with firing temperature. Both the mean and standard deviation of the pore volume-to-surface area values rise with firing temperature. As a measure of the pore volume in relation to its outside surface area, this variable indicates increasing sphericity, which, as with decreasing pore elongation, describes the difference in finer materials and the higher degree of vitrification of higher-fired ceramics compared with low-fired ones; the mean aspect ratio (minimum/maximum eigenvalue) also increases with firing temperature, as the pores become more spherical. The mean of the minimum orthogonal Feret diameter also increases with temperature, another indication of increasing sphericity. Finally, the mean values of the mean Feret diameter and of the maximum Feret diameter increase with temperature; in 3D space, this is related to aspect ratio, which also increases with increased firing temperature.