The clay drying process is one of the most crucial parts of the ceramic process to get right. Not paying attention to the drying process can result in cracking or attachments popping off. In today’s post, an excerpt from her book Mastering Hand Building, Sunshine Cobb gives some great tips on how to manage the clay drying process so that you avoid disasters! -Jennifer Poellot Harnetty, editor.
How do you keep a piece from drying out while you work on it? In most studios, a simple, soft plastic sheet will be your primary tool (I recommend dry-cleaner plastic). The longer you leave a piece exposed to open air, rather than under plastic, the quicker it will dry.
Clay Drying Process: Environment
Besides the covering (or uncovering) of your work, the biggest factor in how fast your work dries is your studio environment. I have been lucky to live in places with a dry climate, so work tends to dry quickly and evenly if it’s not exposed to directional air (for example, an air conditioner or fan). What I love about a dry climate is you can work on multiple pieces simultaneously, easily moving from one to the next when each is ready. Still, it’s always possible for work to dry too fast.
If you live in a humid environment, work can take a while to dry. I have found that covering projects with plastic in high humidity can cause them to become completely saturated, absorbing atmospheric condensation and making pots seem damper than when you first wrapped them. Chances are you will still have to cover pieces when you leave them overnight, and you may need to return to the studio early to uncover them if you want to make progress on finishing them.
Clay Drying Process: Damp and Dry Boxes
Damp boxes are great if you need to rehydrate your work or keep it moist in a dry studio. There’s little risk in using a damp box other than the clay drying out faster than you expected. Use great care when using a dry box, though. It can be a very useful tool in a humid studio, but it can also ruin your work. Set a timer and continually check your pieces until you can begin working on them again. Rapid drying can lead to cracking and other problems, so it’s best to let your work dry at a normal to slow rate. The goal is to allow your work to dry at a steady rate despite the humidity.
Clay Drying Process: Thickness Matters
The next thing to consider in the drying process is wall thickness. I like to make work relatively thin. Besides conserving clay, thin walls help to reduce drying time. The thicker your work, the more patient you’ll need to be.
Once you’re finished working on a piece, the final drying process is, again, dependent on the environment and your clay. Is it picky clay or a fragile object? Will it be exposed to directional air? In general, letting your piece dry slowly helps decrease the chance of it cracking or breaking before firing. If your piece is exposed to directional air, drape some plastic or a bedsheet over it to help it dry at a more even rate. Throughout the drying process, monitor forms that may be prone to cracking or fitting too tight in spots as they dry, such as lids on jars.
Clay Drying Process: Pick the Right Plastic
Not all plastic bags are created equal. In fact, I often refrain from using the term “plastic bag” because what students often think of is the small bag you get from the grocery store or the plastic bag that the clay comes in. Neither of these bag types is great for wrapping your projects. Grocery bags are not airtight. They breathe so well that your work will dry out under them. Clay bags do retain moisture, but they’re so rigid that they can be hard to wrap around projects without trapping a ton of air or damaging your work. I suggest using dry-cleaner plastic. It’s soft, mostly airtight other than the hole at the top created for the hanger, and when cut lengthwise, it becomes a large sheet perfect for flipping slabs or wrapping up a full board of pots. It’s also transparent—a huge plus in communal studios where you want to quickly find your work among others’ on the shelf.
Sourcing dry-cleaner plastic is usually easy. Friends or family may already have extra bags from a recent trip to the cleaners, or you can stop by your local cleaners and purchase a few bags.
Clay Drying Process: Using a Heat Gun or Torch
Chances are if you’ve been in ceramics for a while, you have seen people use a propane torch or a heat gun to speed dry their in-progress pieces. Using a torch or heat gun can be very tempting, and each can be a great tool if used cautiously. I often use a torch in the early stages of a form, getting the foundation to firm up so I can continue building (1).
Here are a few best practices:
- Keep the object moving (preferably on a banding wheel) when applying heat.
- Be mindful about how close you allow the flame or heat gun to get to the form.
- Let the form rest a bit after you have heated it to let the moisture in the clay equalize (the water will migrate, and the clay will steam for a bit).
Here are things to avoid:
- Don’t heat clay that is prone to cracking or a form that is particularly thin.
- Don’t heat the surface where a future attachment is going to be made.
- Don’t heat a seam. It will start to pull apart.
- Don’t heat one spot too much. The goal is to dry your piece as evenly as possible.
- Don’t burn yourself! I prefer a propane torch with a trigger that, when released, shuts off the heat. Heat guns may seem safer; however, once they get hot, they stay hot in places. I have seen many people accidentally burn things they set too close to a hot heat gun or forget that the tool is still hot despite the absence of an open flame.
Clay Drying Process: Fast Drying Done Right
I’ve found one method of fast drying that seems to work better than just leaving a piece to survive in a dry room on its own. However, this requires having your own kiln or the permission of your studio technician or manager.
Place a sheet of dry-cleaner plastic over the piece, covering the form loosely but making sure to cover the whole piece from top to bottom and tuck the plastic under the piece securely. Vent the plastic bag at the top (dry-cleaner bags are perfect for this since most already have a hole for a hanger). Now either place the piece in a dry box or in a kiln set at 180°–200° F (82°–93° C) and hold for as many hours as necessary to dry the piece. (Don’t heat the piece to the point of boiling water, though, or your piece will explode.) Approximately one hour per half inch of wall thickness is the standard drying time or hold pattern I recommend. Note: This should be done only for work that is difficult to dry evenly or work that needs an extended drying period.
Photos: Tim Robinson.
Excerpted from Mastering Hand Building by Sunshine Cobb and published by Voyageur Press, an imprint of The Quarto Group. To learn more, visit www.quartoknows.com/books/9780760352731/Mastering-Hand-Building.html. The book is available for purchase from the Ceramic Arts Network Shop at https://ceramicartsnetwork.org/shop/mastering-hand-building.