Once your pottery has been designed and formed, it is vital that it is completely dry before firing. Failure to do so can compromise the end result, causing the pottery to become frail, cracked or even breaking once in the kiln. The basic premise is that pottery should be dried slowly and steadily in order to be effectively dried throughout. There are, however, many factors that can affect this including climate, the size of your piece, the thickness, and the drying technique you use.
Factors that can affect pottery drying
Climate
A humid climate ensures that your pottery can retain its moisture, even after a week. To negate this, it’s best to give the pottery an extra week or even two - the longer the better to ensure that the pottery is thoroughly dried out.
Dry climates are particularly useful for pottery makers. Even larger sized pottery will be completely dry in a week and maybe even sooner dependent on how it has been stored. However, this can also be a disadvantage as sometimes the clay can dry too quickly and crack or crumble and therefore compromise the integrity of the piece.
The size of your piece
If your pottery is half an inch thick or greater, then it is recommended to leave it to dry for up to three weeks. If you live in a humid climate and want to ensure that the clay is fully dried, then it is worth leaving pottery for an additional week to ensure it is completely dry.
When crafting a larger or thicker piece, it’s worth using extra time to make sure your pottery is totally dry.
The ingredients of your clay
All clays have a different make up, different levels of moisture and different additives. It therefore stands to common sense that the different make up of clays plays a big part in how long it takes for pottery to dry before firing. Clays with a high level of plastic and a finer composition will have a higher water content (similar to porcelain). This means that they will take longer to dry, and shrinkage will be more significant when fired.
It’s worth remembering that the greater the shrinkage, the more likely your clay is to crack.
Adding grog into your clay will help reduce cracking, reduce shrinking and your clay will also dry faster. Grog is essentially finely ground clay that has been pre-fired. The fact that the grog has been fired means that it doesn’t absorb water and therefore dries faster.
Grog does have the slight disadvantage of making the clay less easy to manipulate, so is not suited to more intricate projects.
How to fix uneven drying
Depending on the clay that you use, shrinkage can be anywhere from 2% to 10% during the drying process, which doesn’t include the shrinkage after using a kiln to fire your project.
Clays with the highest shrinkage can crack if not dried evenly and so it’s important to try and ensure even drying.
Testing your clay
Testing your clay is a really important factor in determining how it dries. Not only do you get a feel for the texture and make-up of your clay but you can also test how fast your clay dries and measure the shrinkage rate after it has completely dried through. You can also measure the shrinkage range after firing.
Drying in the sun
Drying your pottery naturally is obviously the ideal way to dry it out thoroughly, however it can cause uneven drying. The issue with uneven drying is that the dry part will pull on the wet part and crack your pottery prior to firing. The best way to avoid this is to dry your pottery in the shade, where it will get an even drying.
Large plates or flat clay projects
The best way to evenly dry large or flat clay projects is to use plywood lined with newspaper. Particleboard is not as effective due to warpage and drywall can dry the clay too fast.
Tenting
Tenting is a perfect way to slow the drying down and to create a long and even process. It is best to allow air into your piece, so use a light piece of plastic like a bag to ensure that it doesn’t touch the clay.
Alternatives For Air Drying
You can use alternatives for drying your clay in order to speed up the process, but they come with risks, as faster drying can cause cracks. Even if you speed the process up, it should still be done in a slow and steady way to ensure a comprehensive drying of the piece. Here are some ways that you can achieve a slightly faster drying cycle.
Candling
You can use your electric kiln to speed up the process (a range of electric kilns can be found at Soul Ceramics). The ideal way to use your kiln is to set the temperature to 82 degrees celsius for 8 to 12 hours. Candling can help to remove any excess moisture from your piece in an even way.
Heat Gun
The heat gun can be a useful method of drying but it can cause uneven drying if not administered properly. Set the gun at a relatively low temperature and carry out the process for less than 15 minutes to ensure a more successful outcome.
Blow Dryers
Dryers can be a tricky device to use for clay drying as they tend to blow hot air too hard on the clay and cause it to dry too quickly. If you want to experiment with a blow dryer, it’s best to use it on the lowest setting and carefully.
Fan
Don’t place a fan so that it blows directly on the piece. A fan should circulate the air to ensure that there is no uneven drying and therefore cracking.
How Do You Know When Your Pottery Is Dry
The main factor to look out for in order to check that your pottery is dry is that the color of your clay turns lighter. Additionally the piece will weigh lighter because the clay will lose around 20% moisture if dried properly. A good test is to hold the clay against your skin - if it still feels cold then it is probably not dry. It should feel like room temperature if dry.
If you need any advice on how to prepare your clay for firing, please do not hesitate to contact our experts at Soul Ceramics who will be able to guide you.
Additional resources on pottery
- How to prevent cracks in pottery
- A guide to raku firing
- Things to consider when you buy pottery clay
- A guide to bisque firing
