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Grilling Season: How to Pit Fire Pottery Using a Good Old-Fashioned Charcoal Grill

Posted By Sumi von Dassow On July 7, 2010 @ 7:15 am In Daily,Features,Firing Techniques,Pottery Making Illustrated | 45 Comments

Pots on the barbie; greenware placed on top of the cooking grill while the charcoal preheats.

Pottery on the barbie; greenware placed on top of the cooking grill while the charcoal preheats.

It’s summertime and that means grilling season is at its peak. But grilling isn’t just for meat and veggies anymore. Why not also use it as a creative tool? Yes, as Sumi von Dassow explains, you can get great pit firing effects on pots using a good ol’ charcoal grill. And, with so many people switching to gas grills these days, you could probably find a cheap charcoal grill at a garage sale, or you might even have one in the back of your own garage!

So if you’re looking for a fun summer activity to try out in your studio, read the article and start experimenting with this backyard pit-firing technique. – Jennifer Harnetty, editor.



It’s summer and time to throw some pots on the barbecue! Yes indeed,
your trusty old Weber grill, the little round one on three legs that
you might have left sitting in your garage when you upgraded your
outdoor kitchen, can have a second life as a mini-kiln. If you don’t
have a kiln but still want to fire some pots—or you have an electric
kiln but you’d like to do some smoke-firing without digging a fire-pit
in your yard or alarming the neighbors too much—the grill is a
surprisingly versatile alternative.

This article appeared in Pottery Making Illustrated magazine’s July/August 2010 issue. To get great content like this delivered right to your door, subscribe today!


Fig.1 Lift out the cooking grid, spread out the coals and put the preheated pots on the coals.

Fig.1 Lift out the cooking grid, spread out the coals and put the preheated pots on the coals.

I used a 22½-inch round grill, achieving a variety of effects with
several kinds of clay and surface finishes. In order to replicate the
look of Native American pottery fired in outdoor bonfires, I fired
pinch pots and small wheel-thrown pots made from micaceous clay. This
clay incorporates small particles of mica in addition to grog, which
makes it beautiful as well as very resistant to heat shock. In New
Mexico it’s traditionally used to make flame-ware for cooking directly
on a fire or on the stove-top. I also tried a variety of smoke-firing
techniques on pots made from smooth stoneware clay that was burnished
either with a stone or using terra sigillata.
Fig.2 Cover the grill but leave the cover cocked to allow for air flow.

Fig.2 Cover the grill but leave the cover cocked to allow for air flow.

Grilling Greenware

To fire greenware on the grill, make pots with walls that are about 3/8-inch thick throughout—no fat bottoms or thin rims—and dry them thoroughly before attempting to fire them. You don’t need to use micaceous clay, but use a clay which is resistant to thermal shock such as raku clay, groggy stoneware, or paperclay.

Fig.3 Surround taller pots with wood scraps. Use newspaper to encourage the wood to burn.

Fig.3 Surround taller pots with wood scraps. Use newspaper to encourage the wood to burn.

Make sure the grill is clean, removing any ashes or partially burned coals in the bottom, then get it going just as you would for cooking, pouring lighter fluid over mounded charcoal and lighting it. Note: Wear gloves and protective eye wear whenever handling pots around the grill, from placing them onto the grid to taking them out of the coals after the firing. As the coals gradually begin to smolder, preheat the pots on the cooking grid above them.

Fig.4 To raise the temperature, use a metal fan to blow air into the partially opened lid.

Fig.4 To raise the temperature, use a metal fan to blow air into the partially opened lid.

 

Fig.5 Remove the hot pot from the kiln and place horse hairs on it to create squiggly black lines.

Fig.5 Remove the hot pot from the kiln and place horse hairs on it to create squiggly black lines.

After 15 minutes or when the coals are turning gray at the edges, quickly and carefully move the pots, remove the cooking grid, spread the coals out and place the warmed pots directly in the hot coals (figure 1). Spread the coals out as you would for cooking, and nestle each pot into the coals. Cover the grill to retain heat, but leave the cover cocked for better air flow (figure 2). Be careful not to rest the hot edge of the lid on the plastic handle of the grill! Out of curiosity, I put a pyrometer inside one of the pots in this firing, and it registered as high as 1300°F, or approximately cone 018. After 30 minutes or so, your pots can be removed. Test them by tapping them to see if they ring, or scratching them with your fingernail. If your pot rings when you tap it and you can’t scratch it easily, it’s fired. Of course the clay won’t be fully vitrified and your pots won’t hold water, but the finished pots won’t disintegrate in water as greenware would. Coals alone reach a temperature of at least 1100°F, and will be enough to fire small pots. For pots above two or three inches tall, or to increase the firing temperature, you might want to pile wood scraps around them to ensure an even firing temperature from the top to the bottom of the piece (figure 3). To increase the heat even more, you can try blowing air into the grill with a fan (figure 4), though it’s possible that doing this repeatedly could shorten the life of the grill, particularly of the charcoal grate. Adding wood to the fire will make it smoke more and consequently the pots will come out with more smoke-markings.
Fig.6 Wheel-thrown micaceous clay, fired green in horsehair decoration.

Fig.6 Wheel-thrown micaceous clay, fired green in horsehair decoration.

Alternative Surfaces

For a beautiful decorative effect, place horse hairs (or other animal or human hair) on the pot immediately after removing it from the fire (figure 5). When working with this technique, remove the pot using tongs, and place it on a piece of warmed soft brick to avoid cracks from thermal shock. The hairs will burn and leave squiggly black marks on the pot (figure 6). Have the hairs ready and work fast—you may only have a few seconds before the pot cools down too much.
Fig.7 This sphere has designs drawn with a gold leaf pen and lines made using copper foil tape.

Fig.7 This sphere has designs drawn with a gold leaf pen and lines made using copper foil tape.

For other alternative firing effects, try burnishing your pots with a stone or applying terra sigillata. Depending on the type of clay you are using, you might want to bisque fire them in an electric kiln and use the grill for decorative effects. I create patterns on pots with copper foil tape (intended for stained glass work), gold leaf pens (figure 7), or masking tape (figure 8). Decorated pots can then be wrapped with a double layer of aluminum foil and placed either directly on the hot coals or on the cooking grid for 30 minutes (figure 9). I placed these tape decorated pieces on the cooking grid instead of in the coals because aluminum foil disintegrates when placed directly on the coals, which can allow smoke to blacken the pot too much. Since the grill can’t produce enough heat to burn off the adhesive on the copper foil tape, this needs to be scraped off after the firing.
Fig.8 This pot was bisque-fired to cone 010, masked with tape, and brushed with terra sig.

Fig.8 This pot was bisque-fired to cone 010, masked with tape, and brushed with terra sig.

I’ve found that different brands of masking tape can have very different effects-—some burn quite quickly and may leave your pot completely black if left on the grill for the full 30 minutes, while other brands have a great deal of sticking power, provide a strong resist and need to be scraped off after firing. The white stoneware piece (figure 10) was brushed with terra sigillata, bisque fired to cone 010, decorated with masking tape, wrapped in a double layer of aluminum foil and fired in the grill.
Fig.9 Place foil-wrapped, tape-decorated pots on the cooking grid rather than on the coals as the foil disintegrates in high heat.

Fig.9 Place foil-wrapped, tape-decorated pots on the cooking grid rather than on the coals as the foil disintegrates in high heat.

One more beautiful effect you can easily achieve firing in your grill is the rich glossy black of burnished and smoke-fired Pueblo Indian pottery. For best results, burnish a smooth red stoneware clay with a stone. If you want to bisque-fire it in an electric kiln first, fire it only to cone 018 to retain the burnish. To blacken it in the grill, wrap it in newspaper and then aluminum foil and place it in the coals. For a deeper black, place it directly in the coals and surround it with wood scraps.
Fig.10 A white stoneware lidded box with masking tape resist decoration after a smoke firing in a Weber grill.

Fig.10 A white stoneware lidded box with masking tape resist decoration after a smoke firing in a Weber grill.

When the wood is burning merrily, cover the grill, shut the air valve on the grill cover and close the cleaning valve on the underside. To protect the burnished surface from getting scratched or marked by the fuel, you can follow the same general steps but start by placing the pot in a coffee can or cookie tin that has holes pierced in the sides. Nestle it into some wood shavings at the bottom of the can, place the can into the coals (figure 11), and cover the can with aluminum foil or a piece of kiln shelf (figure 12). This way, smoke can surround the pot but the pot won’t be in direct contact with burning wood or coals. After 30 to 45 minutes, when the grill has stopped smoking, the pot can be removed. If the pot wasn’t bisque-fired beforehand in an electric kiln, you’ll need to carefully preheat it and fire it directly in the coals to get it hot enough to vitrify—but you’ll probably get the richest black color this way (figure 13).
Fig.11 Place a burnished pot inside a perforated coffee can prior to firing to create an even, glossy black surface.

Fig.11 Place a burnished pot inside a perforated coffee can prior to firing to create an even, glossy black surface.

I’m sure I’ve just scratched the surface in exploring the possibilities offered by this simple piece of equipment. Playing with fire in your barbecue grill makes for an easy and fun project you can enjoy by yourself or with your family—so break out the clay, get some charcoal, and fire away!
Fig.12 Surround the coffee can with wood scraps to create more heat and smoke. Cover the opening with a piece of kiln shelf.

Fig.12 Surround the coffee can with wood scraps to create more heat and smoke. Cover the opening with a piece of kiln shelf.

Clays used

Micaceous clay is available from: Coyote Clay www.coyoteclay.com/clay.html

or New Mexico Clay www.nmclay.com


You can also buy powdered mica and add it to your own clay body.

Red clay for burnishing: Navajo Wheel from Industrial Minerals Company www.clayimco.com

Fig.13 A red stoneware, stone burnished pot, bisque-fired to cone 018, placed inside a perforated coffee can and fired in a Weber grill.

Fig.13 A red stoneware, stone burnished pot, bisque-fired to cone 018, placed inside a perforated coffee can and fired in a Weber grill.

Sumi von Dassow is a frequent contributor to PMI, the author of the best selling book Low-firing and Burnishing as well as the producer of the new DVD Pit Firing & Burnishing. For more information, go to www.herwheel.com. Her book and DVD are available at /bookstore.

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