I spent the afternoon trimming a leather hard plate and using underglazes, sgraffito, and silk screen printing. As I left the studio, I did not cover the plate with plastic. When I returned the next day, the bottom picture is what I found....yikes...CRACKS!!
Non uniform drying is the most common cause of cracking. The clay dries from the outside and shrinks. If it dries too fast , the inside is not shrinking at the same rate and causes stress...thus cracking.
My studio is heated in the winter and tends to dry pottery much faster. To prevent cracking, I need to cover the piece with plastic, uncover for a few hours, cover again, and repeat. This process takes 3 - 4 days.
Other factors can be clay strength and clay that is not the same thickness throughout.