S cracking can occur on pieces that dry unevenly, for instance if you take a bowl and put it in front of a fan. Other reasons for S cracks are leaving water in the bottom of your piece during the drying out phase. To reduce the risk of S cracking:
- Make sure to compress the piece.
- Do not leave water at the bottom of the piece before putting it away for the drying process.
- Tap the center of the underside of the piece that is still in the leather-hard stage with your finger. It may seem that the ever so slight indentation your finger produces is enough to eliminate the S-shaped crack that appears in the drying stage or during the firing process. This simple, but very effective technique, should also work on hand-build flat bottom items.