If you have spent any time with clay, you have probably watched a piece crack — in drying, in bisque, or even after glazing — and felt that gut punch of losing something you put real time into. It is one of the most common frustrations in pottery, and it hits beginners and experienced makers alike.
The good news? Cracking is almost always preventable once you understand what is actually causing it.
What Causes Cracking?
At its core, cracking happens because of uneven stress. Clay shrinks as it dries and again as it fires. When one part of a piece shrinks faster or more than another part, the tension creates a crack. That is really all it is — uneven shrinkage creating stress the clay cannot absorb.
This can happen for a number of reasons:
- Uneven thickness — a thick base with thin walls, or one side thicker than the other
- Drying too fast — especially edges, rims, and handles that are exposed to air
- Joining wet clay to dry clay — the moisture difference creates tension as they shrink at different rates
- Not compressing enough — especially on the bottom of wheel-thrown pieces
- Air bubbles trapped inside — they expand during firing and create pressure cracks
How to Prevent Cracking at Every Stage
During Making
Keep your walls even. This is the single biggest thing you can do. Use a needle tool to check thickness if you are unsure. For hand-built pieces, roll your slabs to a consistent thickness using guides or rolling strips.
Compress your joins. When attaching handles, spouts, or coils, score and slip both surfaces and then press firmly together. Do not just stick wet clay onto leather-hard clay and hope for the best.
Wedge your clay thoroughly. This removes air pockets and creates a uniform moisture content throughout the clay body. Even if your clay feels ready to go straight from the bag, a few minutes of wedging makes a real difference.
During Drying
Slow it down. Cover pieces loosely with plastic and let them dry gradually over several days. The slower and more evenly a piece dries, the less likely it is to crack.
Pay extra attention to attachments. Handles, lids, and any joined areas dry faster because they are thinner or more exposed. Wrap those areas with damp paper towel or extra plastic to keep them from getting ahead of the rest of the piece.
Flip or rotate pieces. If a piece is drying on a shelf, the bottom stays wetter longer. Flip it onto its rim partway through drying so moisture can escape evenly from all sides.
During Firing
Make sure pieces are bone dry. If there is any moisture left in the clay when it enters the kiln, steam will form inside and crack (or explode) the piece. The piece should feel room temperature to your cheek — if it feels cool, there is still moisture inside.
Fire slowly through the early stages. The first few hours of a bisque firing (called the water smoking stage, up to about 400°F/200°C) should be slow. This gives any remaining moisture time to escape without creating pressure.
A Quick Cracking Checklist
- Are my walls even? Check with a needle tool.
- Did I compress the bottom? Especially important on the wheel.
- Did I score and slip my joins? Both surfaces, every time.
- Am I drying slowly and evenly? Cover loosely, rotate, protect thin areas.
- Is the piece truly bone dry before firing? Touch test with your cheek.
Cracking is not a sign that you are bad at pottery. It is your clay telling you something about how it was made or dried. Once you learn to listen to those signals, your success rate goes way up — and that gut-punch feeling starts happening a lot less often.
Track your pieces in the Mud Room app to start spotting patterns — which clay bodies crack more, which forms are tricky, and what drying methods work best in your studio.