Why Clay Cracks (and How to Stop It)
Cracked pots. Not the metaphorical kind — the kind that break your heart after hours at the wheel.
If you’ve ever opened a kiln to find a hairline fracture or watched your bowl split in two before it even dried, you're not alone. Cracks happen — but they don’t have to.
Here’s what causes clay to crack (at every stage), and what you can do to prevent it.
Why Does Clay Crack?
Clay cracks for a few key reasons — and most of them happen before it even reaches the kiln:
Uneven drying: Parts of your piece dry faster than others, causing stress in the clay body
Improper joining: Not scoring and slipping enough means parts separate as they shrink
Clay too thick or thin in places: Uneven walls = uneven stress
Drying too fast (or in direct sun): That lovely sunny windowsill? Often a silent pot killer
Internal air pockets? Actually, not usually the villain — they’re rarely the cause of cracks [source]
How to Dry Clay the Right Way
The drying stage might be the least glamorous, but it’s where most cracks are born. Here’s how we do it at Mayfield:
Dry slowly and evenly: Cover your work with plastic or a damp cloth, especially if one part is thinner or more delicate
Rotate your work: Turn it daily so all sides dry evenly
Don’t place clay directly on plaster or wood: These draw out moisture too fast
Use the plastic test: If it still feels cold on your cheek, it’s not dry
According to Mayco Ceramics, proper drying takes anywhere from 3–10 days, depending on climate, clay body, and thickness.
What Happens in the Kiln
You’ve done your drying — now the fire begins.
Inside the kiln:
Around 100 °C: Physical water evaporates. Rushing this can cause steam to crack your work
300–600 °C: Organic material burns off
573 °C: Quartz inversion occurs — the clay rapidly expands and contracts. If your drying was uneven, this is where you'll see it
1000 °C and beyond: Vitrification begins — clay fuses, hardens, and becomes watertight
Want the science behind firing?
Read our step-by-step firing guide for the full temperature journey.
Clay undergoes physical and chemical changes in the kiln. It dries, burns off organic matter, and transforms into ceramic as temperatures rise — locking its shape and strength permanently.
Studio Tips to Prevent Cracking
Score and slip every join (crosshatch with a serrated rib and use juicy slip)
Compress slab seams and bases while forming
Let bowls dry upside down to equalise rim drying
Dry your pots under plastic overnight or over several days
Don’t rush — cracking is often a sign of impatience, not failure
Final Thoughts
Clay rewards care. The slow, even approach might not feel exciting — but it’s what makes a pot strong, stable, and lasting.
Want to learn these techniques in person? We’d love to show you.
Join a class at Mayfield and fire with confidence.
