No one enjoys a cracked piece. It seems like you can spend all day forming the clay, smoothing it, adding texture, and then find out you have a crack somewhere. The cracks can happen during the drying process, or they might occur after firing. Cracking isn’t something you can always prevent, but there are some things you can do to minimize the chances of having a crack. A basic understanding of why clay cracks helps you to be a better potter.
Why does clay crack?
Clay holds water. The water makes the clay pliable and soft. As a piece dries, the water leaves the clay. That means the clay shrinks. If the different parts of your piece dry at different speeds, or if there is uneven pressure on the clay, the material that has dried will shrink but the wet clay won’t. This creates tension, which results in cracking. It’s easy to understand that thick sections will dry slower than thin sections. But what about forms with internal voids? What about pieces with appendages that attach to the main body? What about places where air can get to the clay easily versus places where it can’t? Understanding how clay dries will help you make less cracked pottery.
Start with a consistent thickness
One of the easiest ways to prevent cracking is to keep the thickness of your clay consistent. If your walls are thick on one side and very thin on the other, they won’t dry evenly. As the clay shrinks, the thicker and thinner sections will pull apart. If you’re throwing or sculpting your piece, don’t rely on the visual appearance of the clay to check the thickness. Look closely to make sure you’re not accidentally leaving a heavy section. This is especially true when making large pieces or pieces with lots of complex curves.
Check the base
Another area where thickness can be inconsistent is the base of the piece. If you leave a thick chunk of clay where the bottom meets the sides, the bottom section will dry more slowly than the rest of the piece. You might end up with a situation where the bottom is still wet but the surrounding clay has dried. That can lead to cracking. Try to make the transition from the base to the side smooth and gradual.
Be careful when attaching clay
Most pots are made of more than one piece of clay. You might be adding a handle, or maybe you’re putting a coil, slab, or decoration onto the piece. Sometimes, just putting two pieces together won’t work. Make sure the areas where you’re joining are prepared correctly and that the moisture level is similar between the two pieces. Attaching a very wet piece to a much drier one could lead to issues when the pieces continue to dry. The attachment should look like it’s part of the form, not just glued or placed on top.
Blend the Attachment
Once you’ve joined two pieces, smooth out the area around the joint so the transition is seamless. A sudden change in thickness can create a weak spot where tension can build up while the piece is drying. Blending the connection will help to spread the tension and can also create a cleaner finish. For bigger attachments, consider if the form needs extra support while it dries.
Avoid Trapped Air and Uneven Construction
The way you construct a form should be guided by what type of form you’re making. Hollow forms need special attention because the walls need to dry evenly and the inside needs to breathe. If a form is sealed completely, pressure and movement of moisture can be a problem during firing. Ensure that your construction is appropriate for firing, and consult with your kiln owner or local studio about whether certain forms should be sealed or vented.
Good construction isn’t just about looks. It’s also about how the form will behave as it transitions from clay to fired pottery.
Regulate the Drying Process
Another common mistake, especially for beginners, is to let a piece dry too fast. Putting freshly made pots out in the sun, next to a heat source, or somewhere that has a lot of air flowing can mean the outside of the piece will dry much faster than the inside. This can put stress on the form and contribute to cracking. Allowing the piece to dry slowly and evenly gives the moisture more time to escape.
Covering the Piece
Depending on what you’re making, it might help to cover the piece loosely with plastic to slow down the drying process. You don’t want the clay to remain wet forever, just avoid rapid water loss. As the piece gets harder, you can allow it to dry more quickly. The best drying method depends on the size, thickness, clay, and construction, so pay attention to your materials and adjust as needed.
Don’t Skip Steps
Because the clay is changing so much as it dries, you need to be patient. If the clay is too wet, it might lose its shape when you handle it, and if it’s too dry, you won’t be able to change it without breaking it. Different stages of dryness are better for different things.
When attaching handles or other additions, the two parts should have roughly the same amount of water content. When carving or smoothing, the clay should be stiff enough to hold its shape, but not quite dry enough to chip.
Finding the right stage can help with construction and finishing.
Be Mindful Of Surface Decoration
Decoration affects drying as well.
Deep cutting, stamping, piercing, and other surface treatments all change the thickness of various parts of the object.
This can cause some areas to dry faster than others.
It doesn’t mean that you shouldn’t decorate, though. Just be aware of what you’re taking away from the pot and whether the rest of it is sturdy enough.
When making a highly decorative surface, don’t forget to look at the inside of the piece, as well as the decorated side.
Watch Out For Abrupt Changes In Thickness
Deep, sharp cuts next to thick areas can leave very weak spots.
Whenever you can, avoid sudden transitions between thick and thin areas, and try not to make anything extremely thin.
That’s particularly true when dealing with sculpture, where there may be many variations in thickness throughout the piece.
Handle Leather-Hard Pots Gently
A pot can seem solid after reaching the leather-hard stage, but it’s still fragile.
Handling a partially dry pot too much will stress the walls and additions.
If the piece is large or delicate, hold it carefully while turning or shifting it.
Try to do the main construction and shaping before the clay is too dry to shape easily.
Any extra handling while the pot is drying just adds another chance for a weak spot to appear.
Look For Early Clues To Trouble
Not every crack comes out of nowhere.
Small cracks can start showing up around handles, seams, bases, and anywhere else there’s a big difference in thickness.
If you see trouble while the clay is still workable, you might be able to fix it instead of letting it get worse.
The specific technique for fixing the problem depends on the clay’s condition and water content, but the basic idea is simple: fix any structural issue before it gets worse.
Letting a piece dry completely before trying to fix a problem can make repairs harder.
Study Cracked Pots
Even professional ceramicists have pieces break.
A crack can teach you something about your clay, your building methods, or your drying conditions.
Instead of throwing away cracked pots, take a close look at them.
See where the crack started and figure out why that part of the pot may have been thicker, thinner, connected differently, or exposed to air differently than the rest. By keeping track of these details, you’ll soon start to notice patterns in your failures and can tweak your methods accordingly.
Be mindful of your environment
The climate in your studio, its temperature, humidity, air circulation, and even what surface a piece sits on as it dries can affect how it performs.
A piece might dry out fine in the winter but could crack when the air is more humid. That’s why there is no set schedule for drying every single piece of pottery perfectly. Instead, keep an eye on how things are in your studio and how your clay reacts to those conditions.
Select an appropriate clay body
There are many different types of clay. Some clays are better suited for very fine work, while others are more robust and are made specifically for sculpting or higher temperature firings. If you’re dealing with consistent cracking issues, the culprit might not be your technique at all. It’s possible that the clay you’re using just isn’t right for the style of work you’re trying to do. Always try to work with clay within the range it was intended to be fired, as the maker or your studio recommends. When experimenting with a clay body for the first time, try making some simple forms to get used to how the clay works.
Make sure the piece is bone dry before firing
Once a piece has been built, it needs to be completely dry before it’s fired. Sometimes a piece might appear dry, but if there are any thick spots, it might still be wet inside. If that happens, water trapped inside the clay will turn to steam and cause big problems as it heats up in the kiln. Be patient and let a piece dry until it’s fully done. Look closely at the thickest parts to make sure that they’ve dried as well. When in doubt, it’s usually safer to let a piece sit longer rather than put it in the kiln too early.
Wrapping Up
To summarize, most cracks in ceramic pieces are caused by moisture, unevenness, construction techniques, and impatience. Build walls evenly, make sure joints are sturdy, don’t make large jumps from thick to thin, and allow enough time for the piece to dry. Pay attention to what’s going on in your studio and be aware of how your clay body behaves. Most importantly, don’t get discouraged when a piece breaks. Each cracked piece can offer clues to what went wrong. Over time, you’ll learn to recognize what could go wrong in your own work, and you’ll develop a more intuitive sense of how to approach each piece with confidence and precision. Great pottery is not only about designing a stunning shape. It’s also about learning to understand the material you’re working with well enough to guide it through each step.