Why Pottery Can Explode In The Kiln

The idea of a piece exploding in the kiln sounds dramatic, and understandably it’s one of the more anxiety-inducing questions newer potters ask at Le Studio Art Space. The good news is that once you understand what actually causes this, it becomes clear that it’s both preventable and genuinely uncommon in a properly run studio. Knowing the real causes takes a lot of the mystery, and the worry, out of the firing process.

Here’s what’s actually happening when this occurs, and what a well managed studio does to make sure it essentially never happens with properly prepared work.

What Actually Causes A Piece To Explode

The core mechanism behind a kiln explosion is trapped moisture or air rapidly expanding as it’s heated, since water turning to steam expands dramatically in volume, and that expansion has to go somewhere if it can’t escape the clay naturally.

If moisture is trapped inside a piece that seems dry on the outside but is still damp within a thicker section, the rapid heat of firing can turn that trapped moisture into steam faster than it can escape through the clay’s surface.

That trapped steam builds pressure until it forces its way out, sometimes violently enough to crack, shatter, or genuinely blow apart the piece, and occasionally damage nearby pieces in the same kiln load. The exact force involved depends on how much moisture was trapped and how quickly the surrounding heat rose around it.

This is fundamentally a pressure problem, not a mysterious or unpredictable one, which is exactly why it’s so effectively preventable once you understand the mechanism behind it. Once you know exactly what causes it, avoiding it becomes a matter of following a few consistent, straightforward habits rather than relying on luck.

Why Insufficiently Dried Greenware Is The Main Culprit

Greenware, meaning unfired clay that hasn’t yet gone through a bisque firing, needs to be genuinely bone dry all the way through before it’s safe to fire, not just dry to the touch on the outer surface.

Thicker sections of a piece, like a solid base or a chunky handle, naturally hold moisture longer than thinner walls, which means a piece can feel dry when handled but still have damp clay hidden within its thickest areas.

This is exactly why patience during the drying stage matters so much, and why rushing a piece into the kiln before it’s genuinely, fully dry is one of the most common preventable causes of this kind of problem.

Drying time varies considerably depending on a piece’s thickness, the clay body used, and ambient humidity, which is part of why there’s no single universal drying time that applies to every piece equally. A simple thin bowl might be ready within a few days, while a thick, solid sculptural form could genuinely need several weeks of patient drying before it’s truly safe to fire.

Air Bubbles Trapped During Making

Air pockets can form during the making process itself, particularly during wedging if clay isn’t thoroughly worked, or during hand building when two pieces of clay are joined without properly eliminating the air gap between them.

Like trapped moisture, trapped air expands under heat and can cause similar pressure problems during firing, even in a piece that’s otherwise completely, genuinely dry throughout.

Thorough wedging before starting a piece is one of the most effective ways to prevent this, since proper wedging technique works out air pockets that might otherwise remain hidden inside the clay body.

For hand built pieces, scoring and slipping joins properly, rather than simply pressing two pieces of clay together, helps eliminate trapped air at seams while also creating a genuinely stronger bond overall. This is a technique worth practising deliberately rather than rushing, since a poor join can cause problems well beyond the firing stage.

How Rare This Actually Is In A Well Managed Studio

In a properly run studio with good drying practices and careful loading procedures, kiln explosions are genuinely rare events rather than a regular occurrence anyone needs to worry about on a routine basis.

Firing schedules themselves are also designed with this risk in mind, often including a slower initial heating rate specifically to allow any remaining moisture to escape gradually rather than rapidly turning to steam under a sudden, aggressive temperature increase.

Experienced studio staff develop a genuine feel for checking whether a piece is truly ready for firing, catching problems before they ever reach the kiln in the vast majority of cases, well before it ever becomes a real issue.

This is exactly the kind of practical, experience-based safeguard that comes from running kilns regularly, rather than something a hobbyist firing occasionally at home might have the same level of built-up intuition for. It’s one of the genuine, if less obvious, benefits of using a shared studio’s firing service instead of firing pieces independently.

What Competing Guides Leave Out

A detail many general guides skip is how a shared studio firing service specifically checks for this risk before loading a kiln, often including a physical check for cool or damp spots on a piece that looks dry from the outside.

What to actually do if you’re unsure whether your own piece is fully dry is another gap worth addressing directly. Holding a piece against your cheek or lip, a sensitive part of your skin, can sometimes detect residual coolness from trapped moisture that your hands might miss entirely.

It’s also worth mentioning that thicker or more complex pieces genuinely benefit from extra drying time, sometimes a week or more beyond what a simple, thin-walled piece would need before it’s truly ready to fire safely. Building in that extra buffer, rather than firing on a tight deadline, is a genuinely good habit for anyone working on more ambitious forms.

Weighing a piece periodically as it dries, until the weight stops changing between checks, is another reliable method some potters use for larger, thicker pieces where visual and touch checks alone feel less certain. A kitchen scale is genuinely sufficient for this kind of home tracking, and it removes a lot of the guesswork from an otherwise subjective judgement call.

How To Make Sure Your Own Pieces Are Firing Ready

Give pieces genuinely generous drying time, especially anything with thick walls, solid sections, or attached handles, rather than assuming a piece is ready simply because a set number of days has passed.

Check for coolness against a sensitive part of your skin, since a piece that still feels even slightly cool compared to room temperature likely still holds residual moisture somewhere within it.

When in doubt, ask a studio instructor to check a piece before it goes into the kiln, since experienced staff at a studio like Le Studio Art Space can often spot signs of insufficient drying that a newer potter might miss.

Following studio guidelines for greenware handoff, rather than assuming your own drying instincts are automatically correct, is a simple, genuinely reliable way to make sure your piece, and everyone else’s pieces in the same firing, stay safe. It’s a small habit that protects the whole kiln load, not just your own individual work.

Frequently Asked Questions

Should I actually be worried my piece might explode in the kiln?

In a well managed studio with proper drying practices and careful checking, this is a genuinely rare event, so there’s no need for ongoing anxiety, just reasonable patience during the drying stage.

How can I tell if my piece is truly dry all the way through?

Checking for coolness against a sensitive part of your skin, like your cheek, can help detect hidden moisture. Weighing a piece periodically until the weight stabilises is another reliable method for thicker pieces.

Does this only happen with certain clay bodies?

It can happen with any clay body if moisture or air is trapped inside, though thicker, denser forms are generally more at risk than thin-walled, simple pieces that dry more evenly and quickly.

Can a piece that explodes damage other pieces in the same kiln load?

It’s possible, which is exactly why studios take drying and pre-firing checks seriously, protecting not just an individual piece but the entire kiln load being fired together.

What should I do if I’m genuinely unsure whether my piece is ready to fire?

Ask a studio instructor to check it before it goes into the kiln. Staff at a studio like Le Studio Art Space are experienced at spotting signs of insufficient drying that can be easy to miss on your own.

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This article is provided for general educational purposes by Le Studio Art Space and reflects common firing safety practice. Always follow your studio’s specific drying and firing guidelines.