Clay Molds Blew up in kiln
Two possible reasons for clay objects blowing up in the kiln:
1) The clay was not completely dry. Clay must be absolutely dry before placing in the kiln. Objects of clay should be relatively thin: plate and tile molds can be 1/8″ thick. Always allow clay to dry for at least a few days before firing. If it feels cool to the touch, it’s probably still damp.
2) Depending on the shape of the mold, there may have been hidden air pockets. Every clay tutorial will tell you that clay needs to be wedged before working it. Wedging clay is exactly like kneading dough. Clay needs to be wedged in order to push out the air pockets. Periodically cut through the clay using a wire cutter and check for air pockets.
Another way to wedge clay is to repeatedly slam the clay onto a surface with some force; reposition the clay ball in your hands each time so that the clay ball remains ball shaped.