Why Did My Pottery Warp in the Kiln?

Clay, drying, firing temperature, thickness, and kiln placement

It can be frustrating to open the kiln and find that a piece that looked perfectly straight before firing has suddenly warped.

Warping is fairly common in pottery, especially with flat pieces such as plates, trays, tiles, slabs, and wide bowls. The good news is that warping usually gives you clues about what happened during drying or firing.

Here are the most common reasons pottery warps in the kiln and what you can do to reduce the risk.

What Does It Mean When Pottery Warps?

Warping happens when a ceramic piece changes shape during drying or firing.

A plate might become slightly curved, a tile may bend upward at the edges, or a bowl may lose its intended shape.

Some movement is normal because clay shrinks as it dries and fires. However, significant or uneven distortion can indicate a problem with the clay, construction, drying process, firing, or how the piece was positioned in the kiln.

1. The Clay Body Can Affect Warping

Different clay bodies behave differently during drying and firing.

Some clays shrink more than others, while some are more prone to movement during firing. A clay body that isn’t well suited to the shape you’re making can make warping more likely.

For example, large flat slabs can be more challenging than smaller, compact forms because they have more surface area that can shrink.

Before making a large project, check the manufacturer’s recommended firing range and shrinkage information for your clay.

2. Uneven Drying Can Cause Warping

One of the most common causes of distortion happens before the piece ever reaches the kiln.

If one part of a piece dries faster than another, the clay can shrink unevenly.

This is especially important with:

• Large plates
• Slabs
• Tiles
• Wide trays
• Flat-bottomed pieces
• Pieces with attached handles or other additions

Try to dry pottery slowly and evenly. Avoid placing a large flat piece directly next to strong heat or in a location where one side receives significantly more airflow.

For larger pieces, covering them loosely with plastic can slow the drying process and give different sections more time to dry at a similar rate.

3. Uneven Thickness Can Lead to Distortion

If one part of your pottery is much thicker than another, those areas may dry and shrink at different rates.

This can create stress in the clay and increase the chance of warping or cracking.

Try to keep the walls and slabs as consistent in thickness as practical.

This doesn’t mean every part of a handmade piece must be perfectly identical. The goal is to avoid large, sudden differences in thickness.

4. Large Flat Pieces Are More Difficult

Flat pottery is particularly susceptible to warping.

A large plate or tile has a lot of surface area that needs to shrink consistently. Even a small difference in moisture, thickness, or support can affect the final shape.

When making flat work, pay close attention to:

• Consistent thickness
• Even drying
• A stable surface
• How the piece is supported during firing
• The clay body’s recommended firing range

Some potters also use appropriate kiln shelves or firing supports designed for their type of work.

5. Firing Temperature Matters

Clay continues to change during firing.

If pottery is fired beyond the appropriate temperature range for its clay body, it can become excessively vitrified and may deform.

This is one reason it’s important to know the recommended firing range of your clay.

Don’t assume that every clay can be fired at the same temperature.

Your clay manufacturer’s instructions should take priority over a general firing temperature you find online.

6. Your Kiln Can Have Temperature Differences

A kiln isn’t necessarily the exact same temperature everywhere inside it.

Different areas can fire somewhat differently depending on the kiln, firing schedule, load, ventilation, elements, and other factors.

If you repeatedly notice that pieces placed in a particular area of the kiln warp while similar pieces elsewhere do not, the kiln environment may be contributing to the problem.

Using witness cones can help you understand how the firing is actually affecting different areas of the kiln.

7. Kiln Placement Can Make a Difference

How a piece sits on the kiln shelf can also matter.

A large flat piece needs appropriate support. If it isn’t sitting evenly, the clay may move during firing and retain a distorted shape.

Make sure the piece is placed on a suitable, stable kiln shelf and isn’t resting against another object.

Avoid stacking or supporting pottery in ways that could restrict its movement unless the method is specifically appropriate for the type of ceramic work being fired.

8. The Shape of the Pottery Matters

Certain designs naturally have a higher risk of warping.

Very wide, thin, or flat forms can be more difficult to fire successfully than smaller, more compact pieces.

If you’re making a large plate, for example, consider whether the design has enough structural support and whether the clay body is appropriate for the project.

Sometimes changing the design slightly can make a major difference.

How Can You Prevent Pottery From Warping?

You can’t eliminate every possibility of warping, but you can reduce the risk.

Try these practices:

• Choose a clay body suitable for your project.
• Keep thickness reasonably consistent.
• Dry pottery slowly and evenly.
• Avoid exposing one part of a piece to excessive heat or airflow during drying.
• Follow the clay manufacturer’s recommended firing range.
• Use an appropriate firing schedule.
• Place pottery evenly on the kiln shelf.
• Avoid unnecessary pressure or uneven support.
• Use test pieces before committing to a large project.
• Keep notes about clay, firing temperature, kiln position, and results.

What If Only Some Pieces Warped?

If some pieces warped while others fired normally, don’t immediately assume the entire kiln is the problem.

Look for patterns.

Ask yourself:

Were the warped pieces made from the same clay?

Were they thicker or thinner?

Were they all large or flat?

Were they positioned in the same part of the kiln?

Did they have the same firing schedule?

Finding a pattern can help identify the cause much faster.

Can Warped Pottery Be Fixed?

Once clay has been fired, correcting significant warping is usually difficult or impossible without changing the piece further.

That’s why prevention is much easier than trying to repair a finished ceramic piece.

If a particular type of project repeatedly warps, make a smaller test piece and change one variable at a time. For example, you might test a different thickness, drying method, clay body, or firing schedule.

Final Thoughts

Pottery can warp because of several factors, including the clay body, uneven drying, inconsistent thickness, firing temperature, kiln conditions, and placement inside the kiln.

The most useful approach is to look for patterns rather than changing everything at once.

Keep track of what clay you used, how thick the piece was, how it dried, where it was placed in the kiln, and how it was fired. Over time, those notes can help you understand what works best for your pottery.

And remember: a warped piece isn’t necessarily a failure. It can be useful information that helps you improve your next firing.

Related Pottery Kiln Guides

• How Hot Does a Pottery Kiln Get?
• How Long Does It Take to Fire Pottery in a Kiln?
• What Happens Inside a Pottery Kiln?
• Can You Put Any Clay in Any Kiln?
• Why Did My Pottery Crack in the Kiln?
• Why Did My Glaze Turn Out Different After Firing?
• How to Choose Your First Kiln

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