The Pros and Cons of Metal Clay Drying Options
Drying Metal Clay Thoroughly Before Firing is Essential!
Most metal clay artists agree that the clay must be bone dry all the way through before it is fired. Any moisture that remains in the center of the clay can cause warping, blisters or bubbles (air pockets created by built-up steam), or even craters (if the bubbles burst open under the force of the steam's pressure)!
Metal Clay Drying Methods: The Trade-Off of Speed vs. Even Drying
In general, choosing a method for drying metal clay involves making trade-offs between speed and even drying (uneven drying can crack or warp the clay). Most artists use more than one method, depending on the individual piece, time constraints, and other considerations. This article describes several different options for drying metal clay and the pros and cons of each approach.
A Word About Warping
Metal clay tends to warp as it dries when the entire piece does not dry evenly at the same rate. The center of the clay dries last, as it is not directly exposed to the air, so the more slowly you dry the clay, the more evenly it will dry and the less prone to warping it will be.
Of course, it's natural to be impatient for your clay to dry so that you can refine it, assemble it with other pieces, if necessary, and fire it. Just be aware that, in general, the more you accelerate the drying process, the less evenly your clay is likely to dry and the more susceptible to warping it will be.
The best way to avoid this is to air-dry pieces rather than drying them with heat, and if possible, to dry them in a way that allows air to circulate around all sides of the clay at the same time. Air drying on a piece of soft, open-cell foam sheet lets metal clay pieces dry evenly but it's fairly slow. You can accelerate the drying process by placing the clay (on the foam sheet) into a food dehydrator to increase the air circulation. Ideally, using a no-heat setting is best and will dry the clay most evenly. However, you can use a low heat setting, if you wish (never use medium or high heat). If you choose to use the low heat setting, don't leave the metal clay in the dehydrator too long to avoid warping. You also can make a homemade metal clay drying box to use with a hand-held hair dryer (blow dryer).
If you are going to dry metal clay on nonstick sheet or another nonporous surface, you can help minimize warping by not lifting your clay from the sheet after the last pass with the clay roller, and after cutting the desired shape, removing the excess clay without lifting the edges of the piece you have cut out. The nonstick sheet has a very slight texture that grabs onto the clay a bit, so the clay is less likely to curl up at the edges if they remain adhered to the sheet.
If you are going to use a hotplate or cup warmer to dry your clay faster, you'll need to monitor the drying and flip the piece over frequently to minimize warping.
The rest of this article will go into more detail about each of these drying methods and their respective pros and cons.
Air-Drying on Open-Cell Foam Sheet
Especially for volumetric pieces that aren't being dried over/around a support, it's a good idea to air dry the fresh clay on a piece of soft, open-cell foam sheet 1/2" to 2" thick. It is often sold by the yard at fabric stores and is sometimes used for upholstery.
- Use foam that is soft and squishy (not dense), which is filled with air pockets and will allow air to circulate around all sides of the clay. This will speed up the drying process somewhat and also eliminate the need to flip the piece over in order to dry both sides.
- Another benefit is that it prevents the clay's surface (whether smooth or textured) from being marred while it's still "wet."
- If you can't find this type of foam by the yard, you can use the thicker piece of foam from a package of Wilton Fondant Shaping Foam or the Ateco Molding Mat for fondant. Both are made of food-grade foam and designed for drying soft fondant cake decorations.
Make a Folded Foam Drying Support
Celie Fago taught me a neat trick, which is to fold a piece of the foam sheet accordion-style to fit inside a drinking glass, mug, jar, etc. While you wouldn't use this method to dry fresh metal clay pieces, there are two situations in which it's extremely useful.
The folded foam is perfect for propping up dried components vertically if you are attaching fresh clay to an edge, which allows the moist clay addition to dry without being marred or distorted by gravity. The photo shows an example of a dried copper clay kimono that I propped up vertically in the folds of the foam so that the fresh copper clay collar pieces I attached could dry without flattening, marring or sagging—all of which would likely have happened if I had laid the pendant flat to dry after adding the collar. I also used the foam to dry a repaired, tapered copper clay rod that had broken in the center. Gravity helped hold the broken ends together until the fresh repair clay had dried. If I had tried to dry the rod horizontally, gravity would have made the tapered ends sag rather than remaining on a straight axis, pulling the two halves apart before the repair clay had time to dry.
Another use for the folded foam sheet in a cup is to support dry metal clay pieces that you've joined together with slip while the joint dries. Nestling the pieces inside the folds of the foam will hold them together with gentle, even pressure so the pieces can't slip or slide as they dry.
Using a Food Dehydrator
A food dehydrator is an excellent way to dry metal clay, providing gentle, even drying when used on low to no heat. The dry, circulating air speeds up drying significantly and is less likely to result in warping than a direct heat source, such as an electric cup or mug warmer or a hotplate.
It's important to use a dehydrator that allows you to dry with no heat or very low heat to minimize the chances of warping.
To protect the fresh metal clay from becoming textured by the mesh screen shelves in the dehydrator, always line the shelf with a piece of nonstick sheet before drying your clay. To further decrease the chance of warping, especially if you are using (low) heat, either use the same piece of nonstick sheet on which you rolled out your clay (without lifting the edges of the clay from the sheet after rolling or cutting) or place it on a piece of foam sheet and put the foam on top of the nonstick sheet in the dehydrator.
Choosing a Dehydrator for Metal Clay
Some of the features to consider include the usable tray space, whether it has a thermostat, where the heating element is located, the efficiency of the airflow, the spacing of the trays, the warranty and the company's customer service reputation/track record.
Round food dehydrators are the most commonly use type for drying metal clay. Here are the advantages of this type:
- Most are fairly inexpensive; sometimes you can find them used or at yard sales.
- They're very common, so they may feel more familiar.
But they also have several disadvantages:
- Most are designed with the heating elements and fans at the bottom, so the temperature varies significantly from the bottom tray to the top tray.
- How efficiently the fans circulate the air can vary widely from one brand or model to the next.
- These units are round and the drying trays are doughnut-shaped, which cuts significantly into their usable area. In fact, you may lose as much as 25% of the tray space because of the "doughnut hole" in the center.
- They trays are stacked so that they rest directly on top of one another. That means means you need to lift off not only the lid but also the upper trays when you want to load or unload pieces on the lower trays.
- The trays are fixed-height, so if you need to dry something tall (or on a piece of foam), you'll need to jury-rig height spacers. You can do this fairly easily by placing three drinking glasses (or even sturdy foam cups) spaced equally around the tray in between your metal clay pieces. However, that not only cuts further into the usable space but also opens up the sides, which prevents the air from circulating efficiently or evenly.
Square Excalibur® Dehydrators
If you're a professional metal clay artist and can justify the cost, square Excalibur brand dehydrators are the best and most versatile on the market. Advantage include:
- Excalibur dehydrators are square and feature a unique and efficient design that gives you use of the entire surface of each tray. You can dry many more pieces at a time, or much larger pieces, than you can in a round model with open-centered trays.
- The trays slide in and out from the front, like drawers. That means:
- You can pull out a tray with one hand and load your pieces onto it with the other hand, which makes loading and unloading much faster.
- You can remove some of the trays to accommodate taller pieces (or pieces that are sitting on a piece of open-cell foam).
- Excalibur dehydrators have built-in thermostats that allow you to control the temperature within a fairly wide range. So you can reduce the temperature to very low to minimize warping. This is a major benefit!
- The company's unique ParaFlexx™ Horizontal Airflow drying system creates a much more efficient airflow for faster, more even drying.
- They come with a generous warranty—5 or 10 years, depending on the model and where you purchase it.
Of course, all these features come at a price; Excalibur dehydrators are significantly more expensive than those from other manufacturers. However, if you make a lot of large pieces, or make a lot of pieces at the same time, or if you teach metal clay classes, you should consider investing in one. For maximum drying space and versatility, I recommend the 9-tray model. Excalibur 3926TB dehydrator
A word to the wise: There are less expensive knock-offs, but they don't have the same quality, reliability or service and support as genuine Excalibur units.
Using a Hairdryer and a Homemade Drying Box
The next best thing to a dehydrator is to use a handheld hairdryer (blow dryer) set on a low temperature inside a homemade drying box. A drying box usually consists of a cardboard box with a hole cut into one of the sides for the hairdryer to poke through. Here's one way to make one.
How to Make and Use a Drying Box for Metal Clay
Making the Drying Box
- Find a cardboard box. such as a shipping box from a package you've had delivered. Choose one that is approximately 12" deep, if possible.
- Cut off the top flaps, or just fold them inside, flat against the sides of the box.
- Cut an opening in the bottom of the box that is just large enough to fit the nozzle of your blow dryer snugly.
Using the Drying Box
- Place the clay piece(s) to be dried on piece of nonstick sheet or open-cell foam. You also can place your clay pieces on a a raised platform or shelf made from a piece of fine stainless steel mesh or screen (see Fine Stainless Steel Mesh Racks for Drying Metal Clay, below), which will allow the air to circulate underneath the clay as well as over and around it. Choose a fine wire mesh to minimize any marks on the back of the clay, unless you like the light texture created by the mesh.
- Place the dryer box upside down and centered over the clay.
- Poke the nozzle of the hair dryer through the opening, and turn the dryer on, using a low-to-medium speed (to avoid blowing the piece around) and a low to medium heat setting (to minimize cracking or warping).
- Turn on the dryer and let it run for several minutes, checking the piece for dryness periodically.
- When the top of the piece is dry, turn it over and continue to run the dryer for several more minutes.
The amount of time required to dry your piece thoroughly will depend on a variety of factors: the size and thickness of the clay piece, what it's resting on, the size of the box, the location of the opening, the speed and temperature of the hair dryer, etc. Most pieces will dry in a total of 10–20 minutes.
Fine Stainless Steel Mesh Racks for Drying Metal Clay
Stainless steel mesh screen made from fine wire is very good for making racks or shelves for drying your metal clay pieces. The air can circulate all the way around pieces that are elevated on the mesh rack, and the fine wire mesh minimizes the likelihood of a pattern imprint on the back of the clay.
You can cut squares or rectangles of mesh to the desired size with wire cutters (or buy a piece that has been cut to a convenient size, which is more convenient but also more expensive for the same amount of mesh). is a good choice. 304 stainless steel mesh sheet with a 0.0016" wire diameter and 46% open area
To make a drying rack, lay the wire mesh over an open frame (or raise the edges with stacks of thickness spacers, the type used to roll out metal clay) or make a drying shelf by grasping each corner of the mesh at a 45-degree angle with parallel pliers and bending it down 90 degrees, thereby creating four "feet."
How Do You Usually Dry Metal Clay?
Which metal clay drying method do you use most often?
Air-Drying on Nonstick Sheet
One way to dry your fresh clay is to place it on piece of nonstick sheet. After one side has dried completely, flip the piece over to allow the reverse side to dry.
Another tip I learned from Celie Fago is to roll out the clay on the nonstick sheet, cut out the shape and remove the excess clay, taking care not to lift the edges of the clay you just cut out. The tension between the clay and the subtle texture of the nonstick sheet helps maintain contact between them as the clay dries, which will help minimize warping. I also like to tape the edges of the nonstick sheet to the work surface to keep it as flat as possible as the clay dries and shrinks.
Remember to flip the piece over after the top has dried to allow the reverse side to dry.
Nonstick Sheet for Metal Clay
You can use nonstick sheet made for food dehydrators, for lining baking pans or ovens or for craft use as long as they are very thin and the surface is very smooth (no Silpat or similar baking sheets). Cut these large pieces of nonstick sheet into several smaller squares or rectangles. I also cut some of this into circles the same size as the flat heating surface of my cup warmer.
Using an Electric Cup Warmer or Hotplate
If you need to dry a metal clay piece quickly—especially something flat—you can place it on a piece of nonstick sheet on an electric cup warmer (also called a mug warmer or candle warmer) or a hotplate. However, because the surface of the clay touching the warmer will dry very quickly, you'll need to turn the piece over every minute or two, at least for the first 5 minutes or so, to try to heat both sides as evenly as possible to minimize warping or cracking. The reason clay tends to warp when dried on a cup warmer is that the surface of the clay that is touching the heated surface dries quickly and shrinks (because the moisture has been driven out and evaporated by the heat and the metal and binder particles are compacted. The rest of the clay (especially if it is thick) hasn't yet dried and shrunk. Visualize a clay slab, and then imagine what would happen if just the bottom surface shrank: the clay that had not yet shrunk (or shrunk as much as the bottom) would start to dome slightly, i.e., warp.
For flat pieces, after you heat the first side for a minute (which will firm up the surface of that side enough to protect the texture), flip it over with a flat metal spatula and press the spatula against the piece for 5 to 10 seconds to keep the piece flat while the other side firms up. Continue to flip and press about once per minute until the clay is dry all the way through to the center. The amount of time will depend primarily on the thickness of the clay.
When you think the clay is thoroughly dry, move the piece from the warmer to a mirror and let it sit for between 5 and 20 seconds, depending on the thickness of the piece. Lift the clay and immediately check for any cloudiness on the mirror. If you see any cloudiness, it's condensation from moisture that's still in the clay, so dry the piece a while longer.
You can also allow the clay to cool completely and then hold it against your chin. If it feels cool, it isn't dry all the way through.
Note: These tests are not infallible, especially for thick pieces, but they do provide a helpful indicator. When in doubt, dry your piece longer than you think you need to!
Combining Drying Methods: The Best of All Worlds
As I said earlier, choosing a drying method for metal clay involves a trade-off between drying a piece quickly and drying it evenly. In some cases, using a combination of drying methods can help you strike a balance between speed and drying evenness.
For example, you might start by air-drying the clay—on a piece of foam sheet or stainless steel mesh shelf or in a dehydrator or drying box—until it's mostly dry and then transfer the piece to an electric warmer to drive out any remaining moisture.
Tip: Even if you have air-dried your piece until you think it's thoroughly dry, it's a good idea to set them on an electric cup warmer for a minute or two (or longer, for thick pieces) as extra insurance. If there is even a very small amount of moisture remaining in the clay when it is fired, it can result in bubbles, craters or worse in the sintered metal.
Questions & Answers
How long should PMC dry in a food dehydrator?
It depends on how thick, long and wide your clay piece is. A thin, small charm might only need 30 minutes, whereas a thicker, larger piece might need an hour or even two. A good way to determine whether your piece is thoroughly dry is to use the mirror test I described in this article.
© 2010 Margaret Schindel