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Kiln Pointers
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How to Make Firebricks Last |
CONTENTS 1) How to Make Firebricks Last 2) Reader Response: estimating the cost of firing a kiln 3) Book Review by Charles Moore on “Clay: A Studio Handbook,” by Vince Pitelka Let me know if you like book reviews or would like to write them. 1) HOW TO MAKE FIREBRICKS LAST Arnold Howard I have seen 10-year-old kilns with firebricks still in pristine condition and one-year-old kilns that looked like they had been dropped from a roof. You can tell at a glance when a kiln has been cared for. Please follow these guidelines to make your kiln last: Vacuum the kiln interior regularly using the brush nozzle of a vacuum cleaner. Be gentle when you touch the firebricks with the nozzle. Apply kiln wash to the kiln’s firebrick bottom. But keep kiln wash away from the walls and elements. (In a glass kiln, you could also use glass separator to coat the bottom.) If possible, do not fire moist greenware. It should be bone-dry and warm to the touch. If you must fire moist ware, wait until all signs of vapor have disappeared before heating past 200 degrees F. The moisture at higher temperatures is not good for the firebricks and can cause the ware to explode. Do not lean too heavily against the firebrick walls while loading and unloading. Some people use a small stepladder to reach into a deep kiln. You can also cut a piece of plywood to fit across the wall that helps protect the wall during loading. Lower the kiln lid (or close the kiln door) gently. Slamming the lid can crack the lid the first time it happens. Fully disengage the lid support before lowering the lid. Forcing the lid downward can break the bricks near the lid hinge. From time to time, check the condition of the lid support and lid handle. Keep the lid closed when you are not using the kiln. This keeps dust out and prevents the lid from dropping while you are away. Do not store anything inside the kiln. The kiln stand should be level and rock-steady. An unlevel stand can stress the firebricks. A stand that rocks can cause the kiln to move when jarred, knocking over ware against the sidewalls inside the kiln. During loading and unloading, do not touch the sidewalls of the kiln with anything. Do not allow a shelf to bump into the firebricks. The extra time and care you spend loading and unloading may add years of life to your kiln. If glaze, glass, or other materials drip onto a kiln wall or the kiln bottom, repair before the next firing. Otherwise these materials will remelt and embed deeper into the firebricks. Remove the contaminant by scraping gently with a putty knife. If you remove kiln wash from the kiln bottom, apply a fresh coat to the bare spot. Do not be concerned about small cracks that appear in the firebricks. The cracks are normal and act as expansion joints. During firing, they close tightly. 2) READER RESPONSE Nuala in Ireland wrote, "Thank you, Arnold, for explaining how much the firing costs! I have been trying to get this information from our national electricity supplier here in Ireland but have never managed to get a satisfactory answer. They would shoot back at me, 'Are you single-phase or 3-phase?' "'C'mon guys, you're my supplier. Surely you should have that info on your records.' "Response: 'Well, no, actually we don't have that info on record. Where do you live again?' "At this stage," wrote Nuala, "I'm just about foaming at the mouth with frustration, so I am grateful to you for giving me the where-with-all to work out the electric costs on firing!" Kathi Martin of Artistry Glass Studios in Chandler, Arizona, USA wrote, "You know, I had my local utility company rep do an energy audit for our business a few years back. I think it cost me about $120. "At the time, I gave her information on my Paragon GL-24ADTSD (top-side-door elements with ceramic top). My programs included all the cooling time after the firing was complete, so it registered from when the kiln shut down at 700 degrees to when it reached room temp. That usually was about 15 hours. That's what I gave her--15 hours of firing time. She used firing time, kiln amps, and the kw cost and told me it cost $13.00 to fire that big bad boy. I was amazed! Only $13.00! "Then I realized that the elements are really on for only about half that time since the cooling doesn't pull power. Now we're down to $6.50 for a full-fuse cycle at commercial electrical rates. "That single piece of information has sold more big kilns for me than any beautiful piece of glass art in my studio. I recouped my $120 in the first big kiln sale." 3) BOOK REVIEW From "Greenware," the publication of the Orchard Valley Ceramic Arts Guild By Charles Moore Sacramento, California USA You can see this book at Paragon’s website: http://www.paragonweb.com/BookInfo.cfm?BID=12 (Go to www.paragonweb.com, click on Products, then Books & Videos from the drop menu.) As soon as Vince Pitelka’s book was published, I bought a copy and began to use it--not just read it, but use it. "Clay: A Studio Handbook" became for me a major reference. I am glad that I have waited to review Pitelka’s work; I have had a chance to live with it and learn by following his advice. "Clay: A Studio Handbook" is perhaps the most comprehensive book on clay work that I have encountered. In addition to the scope of the book, I would note clarity in writing and in explanation of principles, ample illustrations, a concern for safety in the clay studio, and a straightforward presentation. The ten major chapters: Clay and Claybodies; Handbuilding; Throwing; Plaster Working, Mold Making, and Slip Casting; Surface Decoration on Greenware; Glazes and Glazing; Kilns and Firing; Mixed Media in Ceramics; Studio Design, Setup, and Operation (including marketing, photography, and exhibiting). Within each chapter are numerous sub-sections. Because of the scope and thoroughness of the text, I can only hope to sample bits here and there to give a reader a sense for what Pitelka presents. Chapter 2, Handbuilding, for example contains matter Wedging the Clay, Handbuilding: General Guidelines and suggestions, Making Pinch forms, Coil Construction, Slab Construction. Other chapters offer a much greater number of sub-sections. The book also contains a most thorough alphabetical index. Each time I return to the book, I find something that I had missed before. For example, Pitelka presents a paragraph on “Grinding-In” Your Lids. This grinding-in is done when the pot and lid are bone dry: “To accomplish this, hold the pot sideways vertically (with its mouth facing the side) cradled in one hand, and place your other hand flat against the lid with your fingers spread on either side of the handle. Put the lid in place against the pot, and gently rotate it back and forth against its seat several times…rotate it 90 degrees or so, turn it back sideways, rotate the lid back and forth against its seat, turn the pot upright, life the lid and rotate it 90 degrees. Repeat the procedure until you are satisfied with the fit of the lid” (p. 69). I wish I had known this technique when I recently made a small casserole that had top that would fit only if placed in one position. Note the careful detail of Pitelka’s description of “grinding-in.” Early in the book, Pitelka uses a series of twelve photographs to show opening clay on the wheel and basic pulling (p. 47). Then he follows with nine photographs showing in cross sections how the clay would look at each step in the pulling and shaping of a vessel (p. 48). Nothing else could be clearer. In a section on “Vessel Proportions,” Pitelka says, “Vessel proportions vary widely, and unless you are seeking a low spherical shape, these particular forms often look best when the height is at least 1 ½ times the maximum diameter. Also a mix of straight and curved profiles can work very well. For example, the walls might rise straight up six inches from a six-inch diameter base, and then taper inward and flare back outward to a five-inch-diameter rim” (p. 62). Pitelka continues exploring other pleasing proportional variations. Though he is not dictatorial, he offers some valuable advice on proportion. He follows with a section on “Necking In a Vessel” (pp. 63-64). This section is too lengthy for me to repeat, but it is interesting that he presents careful written description of the necking in process and makes reference to a series of photographs. In a series of line drawings, Pitelka presents “Types of Lid and Galleries” (p. 70). Again, nothing could be clearer. Pitelka’s work on “Glazes and Glazing” (pp. 120-159) is thorough without being overwhelming. Though I like to think that I am well acquainted with glaze work, here and there Pitelka teaches me something new. A simple example occurs in the sub-section on “Opacifiers”: “Bone Ash--Calcium phosphate—can give an opalescent satin gloss surface, as microscopic globules of phosphorus remain suspended in the glaze.” p. 146) In another sub-section, “Firing Clay: Chemical and Physical Changes,” I find useful information about what occurs at different temperatures in the firing. Briefly, I will extract some sample temperatures that Pitelka discusses at length: “Around 400°F all free water has evaporated from the work, but chemically combined water is still present. Around 451°F organic materials begin to combust (oxidize). Around 900°F sintering begins.” (pp. 73-174) Though Pitelka continues to present the changes that occur as the temperature rises, this sample is, I think, sufficient to illustrate Pitelka’s vast knowledge of heatwork in the kiln. A few months ago I bought an updraft kiln. I turned to Pitelka’s “Controlling and Correcting Temperature and Atmosphere in an Updraft Kiln” (pp. 180-181). He carefully explains how the damper at the top of the kiln serves to reduce the atmosphere and to even out the temperature from top to bottom. A page later, he presents “Watching the Flame Shape”: “In both updraft and downdraft gas kilns, the shape of the flame entering the burner port can tell you a lot. If the flame tapers rapidly at the burner tip, there is probably too much secondary air, reducing heatwork. If the flame seems to expand and fill the port but there is not reduction, then you have an efficient neutral atmosphere. If the flame spreads out in lazy waves with flickers of yellow, it is getting inadequate secondary air, unless your intention is a reduction atmosphere” (p. 182). I have not found this valuable information elsewhere. Chapter 9 is entitled “Studio Safety and Sensible Studio Practice” (pp. 246-255). Pitelka begins by presenting a “Studio Safety Checklist.” This chapter is a “must read” for any studio potter. When I remodeled my studio recently, I picked up many suggestions from Chapter 10—“Studio Design, Setup, and Operation.” Perhaps the most valuable for me was the sub-section on “Ware Storage.” Pitelka says, “I suppose there is not such thing as a studio with too much shelving, but one does not want to sacrifice space needed for other purposes. My favorite solution is to equip the studio with plenty of ware carts. Rather than viewing them as a device for efficiently moving wares from one place to another, think of ware carts as movable shelving” (p. 259). Following his advice, I have no fixed shelving, but use a series of ware carts of different sizes. One of them has a plastic cover, which serves as a damp room. I have even mounted my slab roller on large, lockable casters. I owe Vince real thanks for this advice; my studio is almost completely flexible. In the appendices at the back of the book, Pitelka presents an extensive and useful “Glossary of [Ceramic] Terms” (p. 316-339) and a “Glossary of Ceramic Raw Materials” (pp. 340-347). Again, his definitions are clear; he has a highly developed sense of reading audience. Finally, I want to finish this review with a philosophical note from Pitelka: “One of the most valuable aphorisms in ceramics is ‘Don’t bond with a piece until it comes out of the glaze firing’” (p. 136). Clearly, I am pleased to own Pitelka’s "Clay: A Studio Handbook," and I recommend it to anyone who is serious about clay work. ----------------- Thanks, Nuala and Kathi, for the letters. It was great to hear from you. I appreciate the book review, Charles. John Hohenshelt and I will be at the NCECA pottery tradeshow in Portland, Oregon March 8 – 10, 2006. If you are attending, please stop by the Paragon booth #628. I would enjoy meeting you. With best wishes, Arnold Howard Paragon Industries, L.P. - Better Designed Kilns 2011 South Town East Blvd. Mesquite, TX 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 ahoward@paragonweb.com / www.paragonweb.com Feel free to email this Kiln Pointer to friends. To read back issues Click here or go to www.paragonweb.com, select “Support,” and then “Kiln Pointers” from the drop menu. To respond to this Kiln Pointer, press Reply. Your email will go directly to Arnold Howard. PRIVACY NOTICE: Under no circumstance do we share or sell your email address. Copyright 2006, by Paragon Industries, L.P. |
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