This makes your pottery strong and solid, and impervious to water and the elements.
The general process of glazing ceramics is first to mix your glaze, apply it to bisque-ware, let it dry, then finally load it into the kiln for the glaze firing. The kiln is slowly brought up to the appropriate temperature for the silica in the glaze to melt, then slowly cooled again. This makes your pottery strong and solid, and impervious to water and the elements.