|Monthly Tech-Tip |
The way in which the walls of this bisque fired kaolin cup laminate reflect the plately and uniform nature of the kaolin particles. Because they are lining up during the wedging and throwing process, the strength to resist cracks is better along the circumference than perpendicular to it. The bonds are weak enough that it is very easy to break it apart by hand (even though it is bisque fired). The worst laminations were at the bottom where wall thickness was the most variable and therefore the most drying stresses occurred. However, if this kaolin were blended with feldspar and silica, this lamination tendency would completely disappear.
Ceramic clays have a flat particle shape. Various factors determine the extent to which they can bind face-to-face in pugged clay in the presence of particles of other materials.
Laminations because of improper pugging of a clay body will cause separations and drying cracks in the ware.