Beginner Info, Blog
Why Does My Pottery Warp? 5 Causes (and How to Fix Each)
After watching one of my YouTube videos, a viewer asked:
Thanks for all the tips! can you tell me a little about drying please. I made some porcelain brooches recently and some of them warped. I think the problem was in the drying….. i think! any help would be brill x
Suzanne Orford, via YouTube
Warping in pottery is a tricky problem to tackle and can occur for a number of reasons, here are my tips to avoid clay warping for small flat items such as broaches, earrings, pendants etc:
- Use a good quality clay and be sure to wedge it well
- Make sure your items are thick enough, my work is at least 3mm thick
- Dry items on a flat hardboard, I use MDF boards
- Slow dry your items, you can cover with plastic to trap moisture and extend the drying time
- Be patient and keep practising, pottery is a craft to learn over a long period
If you don’t currently have flat hardboard’s it is easy to have them made. I recently popped down to B&Q and found a large sheet of MDF which made 6 boards for around £14. They have a cutting service in-store at no extra cost, give them the size of boards you want and you’ll walk out the store with them ready to use!
I’ve seen others place a board on top of their work when drying. This isn’t something I do, my personal experience is this can lead to items cracking.
Now for the longer answer.
Pottery warping can be quite frustrating for anyone who enjoys working with clay. It alters the quality and usability of your finished pieces. Understanding why does my pottery warp? is crucial for improving your pottery skills. It aids in maintaining the correct shape of your creations. For instance, clay memory can lead to unexpected changes. By grasping these reasons, you can prevent issues from recurring. Explore the solutions in this blog to enhance your pottery-making experience!
1. Quality of Clay
Clay Memory
The quality of clay is very important for pottery warping. One key factor is clay memory. This means clay wants to go back to its original shape after you shape it. When you form your clay, it can keep some stress from that process. If you do not handle this well, your pottery might warp when it dries or is fired.
To reduce clay memory, pick clays that have lower plasticity. This helps lower the chance of warping. Also, it is very important to keep moisture even across your piece. Uneven moisture can cause different drying rates, which often leads to warping.
Choosing the Right Clay
Choosing the right clay can greatly lower the risk of warping. Here are some things to think about when picking your clay:
- Choose clays with lower plasticity to lessen memory issues.
- Make sure the wall thickness is even to avoid drying problems.
- Do not use too much water when forming to reduce memory effects.
- Use damp boxes or plastic to help with even drying.
- Roll slabs in different directions to stop uneven compression.
Some types of clay are less likely to warp. The table below shows some of these clays and their features:
| Clay Type | Firing Range (℃) | Characteristics Before Firing | Characteristics After Firing |
|---|---|---|---|
| Kaolin | N/A | High purity, stable, less likely to warp | Durable, withstands high temperatures |
| China Clay | N/A | Lower plasticity, less likely to shrink or warp | N/A |
| Earthenware | 950 to 1100 | Highly plastic, does not warp too much | Softer, porous, less durable |
| Stoneware | 1100 to 1300 | Fairly plastic, easy to work with | Hard, non-absorbent, very durable |
| Porcelain | 1300 to 1346 | Low plasticity, can warp easily | Hard, non-absorbent, very durable, delicate translucency |
By knowing the properties of different clays, you can make smart choices. This will help you create pottery with less warping.
2. Inadequate Wedging
What is Wedging?
Wedging is an important step in making pottery. It means kneading the clay to get rid of air pockets. This also helps make sure the moisture and plasticity are even. This process helps you create a material that shapes easily. If you skip wedging or do it badly, your pottery might warp when it dries or is fired. Good wedging gets your clay ready for shaping. This greatly lowers the chance of warping.
Techniques for Effective Wedging
To get the best results, use these good wedging techniques:
- Wedge the clay until it is even in moisture and plasticity. This makes sure every part of your clay acts the same when you shape it.
- Get rid of air pockets. Air trapped in the clay can grow during firing, causing cracks or warping.
- Test a small pinch of clay. If it feels too stiff, wrap it in plastic and let it rest. If it feels too soft, knead it gently until it is just right.
- Aim for a smooth, workable body. Your clay should respond well to shaping, letting you create the forms you want without problems.
By learning these wedging techniques, you can improve your pottery skills. Good wedging not only makes your work better but also helps you avoid the annoyance of warping. Remember, well-prepared clay is the key to successful pottery!
3. Thickness of the Item
Recommended Thickness
When you make pottery, the thickness of your item is very important. It affects how it looks and how stable it is. Try to keep the wall thickness around 5 to 10 millimetres for most pieces. This thickness helps your pottery dry evenly and lowers the chance of warping. If the walls are too thick, it can cause problems. If they are too thin, they might not be strong enough.
How Thickness Affects Drying
The thickness of your pottery changes how fast and evenly it dries. Here are some important points to remember:
- Thicker pottery walls dry slower than thinner ones. This can cause uneven moisture.
- Different wall thicknesses can make drying harder and raise the risk of warping.
- Thin pieces are more likely to warp because of stress.
Clay memory, or how clay particles are arranged, can cause warping as the clay dries. Thicker walls dry slower than thinner ones, which can make warping worse because of uneven moisture. Also, having the same thickness is very important. If the thickness changes, it can lead to different drying speeds, making warping more likely.
To prevent these problems, make sure your pottery has the same thickness all over. This helps it dry evenly and lowers the chances of warping. Remember, thinking carefully about thickness can really improve your pottery’s quality.
4. Improper Drying Conditions
Drying Environment
The place where you dry your pottery is very important. Things like humidity and airflow can change how your pottery dries. High humidity can change the minerals inside your pottery. When it is moist, salts in the clay can come to the surface. As your pottery dries, these salts can form crystals. This can cause stains on the surface and may lead to warping. So, it is very important to keep a controlled drying environment to avoid these problems.
Tips for Controlled Drying
To dry your pottery properly and reduce the risk of warping, use these helpful tips:
- Dry your pottery slowly and evenly to stop cracks.
- Do not put your pottery in extreme temperatures, like direct sunlight or heat from a kiln.
- Use a damp box for drying, taking off the lid now and then to help it dry evenly.
- When your pottery is nearly dry, put it on a wooden shelf to finish drying.
By using these methods, you can lower the chances of your pottery warping. Remember, being patient during drying times is very important. Taking care will give you better results and improve your pottery-making experience.
5. Why Does My Pottery Warp? Temperature Changes
Effects of Temperature
Changes in temperature can really affect your pottery. Quick changes in temperature while firing can cause thermal stress. This stress can lead to warping, cracking, or even ruining your pieces. For example, firing clay at the wrong temperatures can cause bloating, cracks, or colour changes. If you under-fire your pottery, it can become brittle. If you over-fire it, it can warp and have other problems.
To show how temperature affects pottery, look at this table:
| Temperature (°C) | Effect on Structural Integrity |
|---|---|
| 600 | Initial cracking begins |
| 800 | Significant decrease in compressive strength (up to 50%) |
| 1000-1200 | Loss of structural integrity and mass loss |
Gradual Temperature Adjustments
Making gradual temperature changes while firing is very important to stop warping. You should heat your kiln slowly, especially at the start. This helps trapped moisture escape without causing explosions. Here are some tips for managing temperature well:
- Heat slowly at low temperatures, especially during the first 200-300°F.
- Vent the kiln or keep peepholes open at the start to let water vapour and gases out.
- Increase the temperature faster than during bisque firing, but avoid quick jumps.
- Keep peepholes closed after the first few hundred degrees to keep heat steady.
By following these tips, you can lower the chances of warping in your pottery. Remember, being patient during firing helps improve the quality of your finished pieces.
Pottery warping can happen for many reasons. These include the quality of clay, poor wedging, thickness, drying conditions, and temperature changes. To stop warping, you should:
- Pick clay that has lower plasticity.
- Make sure to wedge well to remove air pockets.
- Keep the thickness even all over your piece.
- Control the drying conditions to prevent uneven moisture.
- Change temperatures slowly while firing.
For helpful solutions, think about watching videos that give tips from experience. You can also check out resources like the Xiem Tools Batmate 14 Inch Bat Jitter & Warping Solution and the Xiem Tools Batmate 12 Inch Bat Jitter & Warping Solution. Remember, getting better takes practice and patience!
FAQ
What causes pottery to warp during drying?
Pottery warps when it dries because of uneven moisture. If some parts dry quicker than others, stress builds up. This stress can cause warping. Always make sure your pots have even thickness and moisture.
How can I prevent warping in my pots?
To stop warping, pick the right clay and wedge it well. Keep the thickness consistent. Control the drying area and avoid quick temperature changes when firing. These steps help keep your pots stable.
Is it normal for freshly thrown pots to warp slightly?
Yes, slight warping can happen with new pots. You can reduce this by using good techniques when shaping, drying, and firing. Being consistent in these steps lowers the chance of noticeable warping.
Can I fix warped pottery after it dries?
Fixing warped pottery after it dries is hard. You can try reshaping it while it is still damp or use a damp sponge to soften the edges. However, it is better to prevent warping than to fix it later.
What is dry footing, and why is it important?
Dry footing means making sure the base of your pottery is dry and even. This method stops warping and helps with stability during firing. Good dry footing keeps your pots strong.
