Drying Metal Clay

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. Drying on a piece of soft, open-cell foam sheet is a good method. You can accelerate the drying process by placing the clay (on the foam sheet) into a 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.. Or you can make a homemade drying box to use with a hand-held hair dryer (blow dryer).

If you are going to dry your metal clay on a non-porous surface, such as a piece of non-stick sheet, 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 non-stick 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 a 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 lens will go into more detail about each of these drying methods and their respective pros and cons.

A food dehydrator is an excellent way to dry metal clay. 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 non-stick 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 non-stick 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 non-stick sheet in the dehydrator.

The best and most versatile dehydrators are the Excalibur® brand. Most dehydrators are designed with the heating elements and fans at the bottom, so that the temperature varies significantly from the bottom tray to the top tray. And the efficiency with which their fans circulate the air can vary widely from one brand or model to the next. The units are round and the drying trays are donut-shaped, which cuts significantly into their usable area (you lose as much as 25% of the tray space because of the "donut hole"), and they're stacked, which means you need to lift off the lid and the upper trays 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're out of luck. (You can jury-rig height spacers by placing three drinking glasses spaced equally around the tray, but that not only cuts further into the usable space but also opens up the sides, which interferes with the air circulation.)

By contrast, Excalibur dehydrators are square rather than round, and feature a unique and efficient design that gives you use of the entire surface of each tray. The trays slide in and out from the front, like drawers, so you can pull out a tray with one hand and load it with the other hand, which makes loading and unloading much faster. You can remove some of the trays, if you wish, to accommodate taller pieces or pieces that are sitting on a piece of foam. The Excalibur dehydrators have built-in thermostats that allow you to control the temperature within a fairly wide range, and the company's unique Parallexx™ Horizontal-Airflow Drying System creates a much more efficient airflow for faster, more even drying. The design also makes cleaning much easier.

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. Many metal clay instructors swear by their Excaliburs. And you often can get great deals on eBay.

There are made-in-China knockoffs that have "borrowed" many of the design elements of the American-made Excalibur dehydrators, but there are differences in the quality. While hardly unbiased, this article by the Excalibur staff explains some of the key differences between the originals and the knock-offs.

If you don't need or want to invest in an Excalibur, of course, there are many dehydrators that are far more affordable. When choosing one, 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.

The next best thing to a dehydrator is to use a hand-held 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.

Making and Using a Drying Box for Metal Clay:

• First, find a cardboard box. (such as a shipping box from something you've had delivered to you). 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.
• Place the clay piece(s) to be dried on piece of non-stick 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, which will allow the air to circulate underneath the clay as well as over and around it. However, if you place the clay directly on the mesh, it might leave marks on the clay or cause cross-contamination if not cleaned thoroughly before switching between different types of clay.
• 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.

One way to dry your fresh clay is to place it on piece of non-stick sheet. After one side has dried completely, flip the piece over to allow the reverse side to dry.

A tip I learned from Celie Fago is to roll out the clay on the non-stick sheet, cut out the shape and remove the excess clay while 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 non-stick sheet helps maintain contact between them as the clay dries, which will help minimize warping. (I like to tape the edges of the non-stick sheet to the work surface to ensure that it stays as flat as possible.)

Remember to flip the piece over after the top has dried to allow the reverse side to dry.

If you need to dry something quickly - especially something flat - you can place it on a piece of non-stick sheet on an electric cup warmer (also called a mug warmer or candle warmer) or 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.

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.

Note: This test is not infallible, especially for thick pieces, but it's a helpful indicator. When in doubt, dry your piece longer than you think you need to!

As I said earlier, choosing a drying method for metal clay involves a trade-off between drying it quickly and drying it evenly. In some situations, you way want to use a combination of drying methods to strike a balance between speed and even drying.

For example, you might start by air-drying the clay (on a piece of foam sheet or a 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 finish removing any remaining moisture.

Tip: Even if you air-dry your pieces until you think they're thoroughly dry, you can set them on an electric cup warmer for a minute or two (or longer, for thick pieces) as extra insurance that every bit of moisture has been removed from the clay before it's fired.

This lens is copyrighted by the author and is protected by a Creative Commons "Attribution-NonCommercial" license. You are free to share this lens and to adapt the content with proper attribution and for non-commercial use.

Exception: If you are teaching a class, you are welcome to distribute unaltered, printed copies of this lens along with the link information.




This
work is licensed under a
Creative Commons Attribution-NonCommercial 3.0 License.

©2009–2012 Margaret R. Schindel. All rights reserved.