Imagine you’re a potter who’s been hard at work creating a new sculpture. You’ve got the clay just the way you want it, and you’re ready to start drying it. But just as it starts to take shape, you notice that the clay starts to get hairline cracks. What can you do to prevent your clay from cracking?
Clay needs to be compressed when forming it, then it needs to dry evenly. Make sure the pottery is covered, so it does not dry too quickly to prevent your clay from cracking.
I understand how frustrating it feels after you’ve molded the perfect piece, and it cracks while drying. My article will offer advice and strategies to overcome those struggles so that your clay doesn’t crack when drying.
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Why does clay Crack while Drying?
Wet clay consists of tiny particles surrounded by water. As the water evaporates the clay particles shrink together closing the gaps in the clay. Here are a few reasons why clay cracks while drying.
The main reason why your clay will crack is from uneven drying. If one part of the pottery dries faster than the other, it can cause the piece to crack.
Clay particles are made up of very tiny, thinly sliced platelets that are stacked together and arranged randomly. These wet and dry particles push against each other during the drying process, causing tension and possible cracking.
Another reason why your clay will crack is that it dries too quickly. When the clay dries too quickly the water in between the clay particles starts to evaporate, pulling the clay particles close together. Drying too quickly can put tension on these clay particles, which can cause the clay to crack.
The third reason is that the clay may not have been compressed correctly when it was formed. For example, suppose there isn’t enough pressure on the clay to compress and align the clay particles. In that case, the clay particles will stay disorganized and will often crack as it starts to dry. This is because these tiny clay particles are now pushing against each other, thus forming a crack.
Steps to Prevent Clay Cracking
Clay cracking when your pottery is drying can ruin all your hard work. The good news is that you can take steps to prevent your clay from cracking while it dries. Follow these steps to ensure that your clay doesn’t crack while it dries.
1. Control the Clays Drying Time
One of the best ways to prevent your clay from cracking is to understand how the clay dries and control the clay’s drying time. Clay dries in Three stages.
First Stage of Drying
The first stage of drying is when the water is in-between the spaces in the clay particles.
This high moisture content is what makes the clay malleable (flexible), allowing you to mold the clay.
Second Stage of Drying
The second stage of drying is when the clay becomes leather hard. The water has evaporated enough to harden the clay a little more.
At this stage, you can trim, add handles, and make other alterations. Even though the clay has less water content the clay particles are still moving because the water continues to evaporate in-between the spaces in the clay particles.
Third Stage of Drying
The third and final stage of drying is when most of the water has evaporated from in-between the spaces in the clay particles. At this stage, the clay particles are no longer moving but there is still water present in the clay.
The clay needs to dry more slowly during the first and second stage of drying. If it dries too quickly, the water in the clay can start to evaporate unevenly. Then one part of the clay is moving, and the other part is not. This puts pressure on the clay particles and causes the clay to crack. Slow drying is the best way to dry your clay evenly.
2. Consider what type of clay body you choose.
When it comes to pottery making, the Type of Clay Body you Choose is important. Different clays have different rates of shrinkage. The higher the shrinkage rate the more likely pottery clay cracks.
Porcelain can shrink anywhere from 12 to 20%. While the shrinkage rate of Stoneware is around 12 to14%. A low fire Earthenware has a less shrinkage rate of 4 to 7%. The higher the shrinkage rate, the greater chance you have of your clay cracking.
Grog in Clay
Consider choosing a clay with grog. You can also add grog to your clay. Grog is made up of broken pieces of fired clay and ground up. Grog is ground up into fine, medium, and large bits.
Grogged clay shrinks less and helps to add strength and stability to the clay. Which can help prevent cracking while the clay dries. In addition, the finely ground nature of the fired clay means that water won’t be absorbed, which also speeds up drying time!
Paper Fiber in Clay
You can also add paper fibers to your clay body or use paper clay. This Porcelain Paper Clay helps to prevent the clay from cracking when drying.
3. Wedging Your Clay to Prevent Cracks
Wedging your clay is an important step in preventing it from cracking while drying. This helps to compress and align the clay particles, which helps prevent cracking.
It’s important to wedge your clay correctly so that it has an even consistency throughout. You don’t want hard lumps that are drier in your soft clay. This will result in uneven drying.
I have an in-depth article with a video on wedging clay click How To Wedge Clay A Beginner’s Guide With A Step By Step Video
4. Compressing the Clay (Hand Building and Wheel Throwing)
Compressing the clay is the act of pressing down on the clay and smoothing it out. This technique helps align the particles and keep cracks from forming.
If there isn’t enough pressure on the clay, these tiny particles remain disorganized. In addition, when the clay particles are disorganized, they place more pressure against each other as the water evaporates, which can cause the clay to crack.
When the clay particles are more aligned, they have a better chance of bonding together as they dry. Hand-building pottery and wheel-thrown pottery require different compressing techniques.
Hand Building Clay Compression
When hand-building clay, use a Rubber Rib to compress and smooth out the clay. Place the rib on a slight angle onto the clay. Then, lightly move the rib to smooth the surface area and compress the entire piece evenly.
One of the most important steps in preventing your clay from cracking when slab building is to roll out your clay, then flip your clay over to align the particles on both sides. This helps to prevent the clay from warping.
Also evening out the thickness of the clay when hand building. This will help prevent cracking because the clay will be drying at a more even rate.
Compress the Clay on the Pottery Wheel
When throwing pottery on the wheel, you need to compress the clay. You are compressing the sides and aligning the clay particles while you are throwing your pot. However, the rim and the bottom of the pot are not being compressed.
It’s important to compress the rim and smooth out the surface of the clay to avoid small cracks on the rim of your pot. First, hold the sides of the rim with your anchor hand thumb, and index finger. Then place the index finger of your outside hand on the top of the rim and slowly turn the wheel.
Compressing the Bottom
The bottom needs to be compressed to avoid S cracks. You can do this by pressing down on the clay with your fingers or using a sponge. This will flatten and align the clay particles. This helps to decrease the water absorption of the clay, thus keeping the clay stronger longer. I do this once after forming the base of the clay and when I finish my pottery piece.
To make sure the base of a pot is not too thick. A thicker base or uneven thickness can cause the clay to crack. Use a needle tool to check the thickness.
Slide your index finger down the needle tool until your finger touches the clay. Keep your finger in place on the needle as you remove the needle tool away from the clay.
The thickness of the base is the distance between your finger and the tip of the needle.
5. Attaching Handles, Knobs, and Features to your Clay
Handles and different attachments can add a lot of character and function to your pottery. Unfortunately, they are also weak spots on the pottery and can be a place where cracks often form.
When adding handles, knobs, or other features, it’s important to wait until the pottery and attachments are in the same drying stage. This is the second stage of drying when your clay is leather hard. You can no longer mold it at this stage, but the clay is strong enough to hold the attachment in place.
To help ensure the attachment does not crack on your pottery, it’s important to score both of your pieces
Then apply slip to both your handle, knob, or feature and piece. Once both pieces are scored and slipped, attach them together.
This will help to create a strong bond between the handle and the pottery. It is also a good idea to smooth any sharp edges on your pieces of clay with a Finishing Sponge.
I never have problems with my attachments when I do it this way. It is also best that your slip is the same clay body as your pot and attachment.
For more detailed information on attaching handles go to my article on Attaching Handles.
6. A Drying Area or Room for Your Pottery
Once you’ve molded your clay, you need to find a place to let it dry slowly and evenly. This drying technique is one of the best practices to prevent cracks while drying. If a pottery piece is left out in the open, The rim will dry faster than the sides and base of the pottery.
There are several places to dry your clay. You can use a damp box, a portable greenhouse, a drying room, or a designated drying area.
Using a Damp Box to Dry Pottery
A damp box is a great way to dry your pottery. The moisture level in a damp box is even and will allow your clay to dry evenly and slowly as the moisture slowly escapes from the covered box.
You can make your own damp box by using a Plastic Container with a Cover. Make sure the top of the container is not sealed so that the moisture can slowly escape.
Portable Greenhouse for drying pottery
Another way to dry your pottery evenly is a Portable Greenhouse. A portable greenhouse will allow you to control the humidity while your pottery dries. This will keep your moisture level even while your pottery dries.
A Drying Room for Drying Pottery
You may be lucky enough to have a whole room designated for drying your pottery. Like a Greenhouse, a Drying room will also help keep the moisture even as the pottery dries, so you don’t have to cover your pottery.
Tenting Your Pottery
Tenting is covering the top of your pottery with a sheet of plastic or a plastic bag. Set up an area where your pottery can safely dry. Do not seal the plastic bag around the pottery. Tenting helps to keep the top of the pottery from drying faster than the bottom. Allowing the water to evaporate from the clay more evenly and slowly with not too much air exposure.
I like to use Clear Plastic bags so I can see my Pottery and don’t accidentally hit a piece of pottery.
7. Arrange Your Pottery for Proper Drying
Separating your pottery pieces for drying is an important step in drying. You can do this by spreading out the pieces so that they’re not touching each other. You will want to place your pottery at least an inch apart for air to flow in between them.
Your handles and attachments should be positioned facing inward so they don’t dry faster than the pottery piece they are attached to. You can also carefully wrap the handles in plastic for the first few days of drying.
8. Rotating the Pottery
Rotating and turning your pottery over is important in the drying process to prevent a cracked area from forming. Turning the piece over. Helps to ensure that the pottery dries evenly and doesn’t crack. By rotating the pottery, you allow all the pieces to dry at the same rate.
This is an important step in the drying process that will help to prevent any cracking from occurring.
9. Properly Drying your Pottery
To ensure that the clay dries evenly, you should allow the pottery to dry slowly for several days.
Depending on the type of clay, 20% to 30% of the clays body weight is water. So, you want the water to evaporate slowly and evenly to prevent pressure from being put on the clay particles from wet and dry clay.
When Using a Damp Box
After a day, remove the lid from the damp box for an hour or two, depending on the climate you live in. If you live in a dry climate, an hour is fine. Rotate and turn your pottery over; replace the lid on your damp box.
Repeat this process the next day. Check your pottery daily until the clay has reached the final drying stage.
When Using a Portable Greenhouse
After a day, you should unzip the door for the greenhouse to allow the moisture to escape. An hour or two is fine. Then rotate the pottery carefully by turning and flipping it over.
Repeat this process the next day. Check your pottery daily until the clay has reached the final drying stage.
When Using a Drying Room
If your drying room is not climate controlled after the first day, open the door or window for a few hours to release some of the moisture. Then carefully rotate your pottery and close the door.
Repeat the process the next day. Check your pottery daily until the clay has reached the final drying stage.
When Tenting Your Pottery
After a day of tenting your pottery, remove the plastic for an hour or two to release some of the moisture. Rotate the pottery and cover again with the plastic bag. This will help equalize the moisture so the clay can dry more evenly.
Repeat this process the next day. Check your pottery daily until the clay has reached the final drying stage. The time it takes will depend greatly on the climate you live in.
10. Find a place to let the clay dry in the Final Stage of drying
The final step is to let the pottery air-dry. You can do this by leaving the pieces out to dry naturally. At this stage, the clay has little water left, and the clay particles are no longer shrinking or moving. You can remove your pottery from under your plastic bag, damp box, damp room, or portable greenhouse to complete drying.
Then place the pottery on a rack, like a Cookie Rack. Depending on the amount of greenware you have you can also get a Steel Rack Shelving Unit. This will allow the air to get under nether the pottery to help the final drying process. You can also use a fan for greater airflow or candle your pottery at this point.
Make sure that the pieces are bone dry before firing them in the kiln.
How to Know Your Pottery is Bone Dry
Bone dry clay will feel room temperature when held to your cheek. Keep in mind the room will be cooler than your cheek unless the room is over 98℉ or 37℃.
The clay will also be lighter in color than when it is wet. The clay will feel cold if it still has moisture in it.
Can you use heat to dry your pottery?
Yes, you can use heat to help dry your clay projects. Heat can be used to dry your pottery in several ways, but you must exercise caution.
Using a Heat Gun:
Heat guns are mainly used for wet pottery. This helps the clay stiffen to prevent it from collapsing. The heat should be distributed as evenly as possible to prevent cracking.
Set the gun temperature at 120 and keep the gun at least 5 inches away from your clay. A heat gun is not used to dry the clay completely.
Candling is a term used for drying your clay in the kiln. Place your greenware in the kiln. Set your kiln to 180 degrees Fahrenheit (82 degrees Celsius) for 8 to 12 hours. Candling will take out any moisture left in your pottery evenly and much faster than air drying.
However, candling is only recommended to do when your ceramic clay is in its final stage of drying. It is not recommended for clay with too much water in it. There are several reasons for this. First, it can increase the chance of your clay cracking. It’s harder on the elements in your kiln (Electric Kilns hate moisture). Plus, it is not energy efficient.
Placing Greenware Next to Your Kiln:
Another way to speed up the drying process is to place your pottery near your kiln when you are firing another load of pottery. This should also be done with clay in the final stage of drying. Wet or leather hard clay will dry too fast and unevenly around the kiln. Plus, it is not recommended to place ANYTHING on the top of your kiln.
Can You Fix a Crack in Bone Dry Clay?
If you love the piece and want to try and save it, you can try a mixture of Vinegar, a little toilet paper, and clay. It must be the same clay as your cracked pottery. Mix it to the consistency of sour cream and gently rub the mixture into the crack. Let dry and hope for the best.
There is no guarantee that this will work, but it’s worth a try if you’re attached to the piece. Bone dry clay is very difficult to work with, so it’s important to be careful and take your time. If the crack is small, you may be able to repair it without too much trouble. However, if the crack is large or runs through the entire piece, it may be best to start over.
How Long Can You Store Pottery Before Bisque Firing?
Once your pottery is completely dry, you can fire it in the kiln. If you’re not going to be firing your pottery right away, you can store it for an indefinite period of time.
However, your bone-dry pottery is extremely fragile at this stage. Your environment could destroy the bone-dry clay. Therefore, you need to store your pottery in a safe area where it will not get damaged.
You can store your pottery in boxes. You can also store your pottery in cabinets or bins to make sure that they are protected. Make sure that the area you choose is dry. This will help to prevent the pieces from growing mold.
In this article, we discussed how compressing and properly drying your pottery is essential in preventing cracking. By following these tips, you can ensure that your pottery dries evenly and doesn’t crack while it dries!
If you’re looking for more tips on how to prevent your pottery from cracking, be sure to check out my other article on How Long Pottery Should Dry Before Firing. Thanks for reading!