Few things hurt more than opening a kiln to find your best piece split down the middle. Pottery cracks have specific causes, and most are preventable once you know what to look for.
S-Cracks (Bottom Cracks)
An S-shaped or X-shaped crack in the bottom of a thrown piece is the most common cracking pattern. It happens because the clay at the bottom didn't compress properly during throwing, leaving weak spots that crack as the piece dries.
The fix: when you finish throwing, use a rubber rib or your finger to firmly compress the bottom from the inside. This aligns the clay particles and seals weak spots.
Rim Cracks
Cracks at the rim usually mean the rim dried faster than the rest of the piece. Thin areas dry first, and if the bottom is still wet, the rim shrinks and pulls.
The fix: cover the rim with plastic while the bottom catches up. Even out drying speed by wrapping the whole piece loosely in plastic and letting it dry slowly over several days.
Joint Cracks (Handbuilding)
In handbuilt pieces, cracks often appear at joints — where a handle meets a mug, where coils were stacked, where slabs were attached. This means the joint wasn't strong enough.
The fix: score and slip every joint. Score = scratch the surfaces. Slip = apply liquid clay between them. Then press firmly and smooth. Half-hearted joints crack every time.
Kiln Cracks
Cracks that appear after firing — especially clean breaks through thick areas — usually mean the piece had thickness inconsistency or trapped air. Thick parts heat and cool at different rates than thin parts, creating stress.
The fix: aim for consistent wall thickness throughout. Compress closed forms slowly to avoid trapped air pockets. Hollow out solid sculptures.
Glaze Cracks (Crazing)
Fine spiderweb cracks in the glaze surface aren't structural cracks — they're called crazing. The glaze contracted more than the clay body during cooling. Some potters consider crazing decorative; in functional ware, it's a problem because bacteria can lodge in the cracks.
The fix: use glazes formulated for your clay body. Our studio uses tested glaze/body combinations to prevent crazing.
Prevention Routine
- Compress bottoms thoroughly
- Dry pieces slowly under plastic
- Score and slip every handbuilt joint
- Keep wall thickness even
- Use clay and glaze that are formulated to fit together
Cracks happen even to experienced potters. They're part of the process. But with attention to these patterns, you'll lose far fewer pieces. Join the waitlist for opening updates.
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