As Sumi von Dassow explains in today’s post, 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 activity to try out in your studio, read the article and start experimenting with this backyard pit firing technique. – Jennifer Harnetty, editor.
Pit Firing Without the Pit!
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. 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.
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.
Pit Firing Pottery in a Weber Grill
To pit 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.
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 pit firing. As the coals gradually begin to smolder, preheat the pots on the cooking grid above them.
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.
For a beautiful decorative effect similar to horse hair raku, 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.
For other alternative pit 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.
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.
One more beautiful effect you can easily achieve pit 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.
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).
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!
Red clay for burnishing: Navajo Wheel from Industrial Minerals Company – www.clayimco.com
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 in the Ceramic Arts Network Bookstore.