Jul 5, 2013

Posted by | 20 Comments

Exploding Clay

My kiln is in the back of my classroom. Due to the smell from firing, I never fire the kiln when my students are present. I turn on the kiln at the end of the day. One day, I stayed after school to catch up on grading. After the kiln had been on for three hours, I heard it: the infamous popping sound coming from the kiln. I immediately knew what happened…Someone’s clay piece, their precious artwork, exploded.

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I ran through all the reasons how their clay project could have blown up. Was it too wet? Maybe there were too many air bubbles? Was it my fault? I immediately felt guilty. I probably didn’t let them dry out long enough. I thought I did…

Worst of all, what was I going to say to the student? How was I going to explain that the artwork they worked on for a week exploded? What if it hit another piece and that project exploded too?  Luckily, in most cases, the students are able to remake their projects. If I’m pinched on time, I have them re-make them in air-dry clay. Is it the same? No. Does it give them a project to take home? Yes. Not to mention, it creates a learning experience for all of us.

Have you ever heard the awful popping sound from your kiln?

How do you handle situations when clay projects explode?



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  • Emily

    I had about 8 clay dinosaurs explode once. With it being so many I’m pretty sure it was teacher-error (not enough drying time). There were heads, tails, and legs everywhere! Students decided it was the true reason the dinosaurs are extinct. A few students only lost a leg or tail, they did not remake it, instead they pretended the dino had been in a battle. The others came in during recess to remake theirs. Because it was definitely my fault, and I had the clay, they remade the dinos with real clay and I fired them.

    Since then I give ample drying time, and the worst thing that’s happened is pieces that weren’t scored properly fall off or break. Those students glaze the pieces and after it’s glaze-fired I get out the hot glue gun.

    I also learned from a veteran art teacher about “candling”, or firing the kiln on a low temperature for several hours to help things dry out faster before actually firing them.

    • Amanda Heyn

      Emily, I was going to mention candling too! I always do it, and I’ve never had an explosion.

  • Lynn

    I had something worse than that happen. While firing a load of middle school projects, we had a power outage for about 30 minutes. When the power came back I reset the timer for 12 hours, The timer is a backup to a kiln sitter that shuts off when a cone melts. The next morning I opened the kiln to see all the projects had melted and were stuck to the shelves. Since the kiln was only a few months old, I was determined to find out what went wrong. I finally called the cone manufacturer and was told that once the cone is heated to any temperature, it solidifies and will not melt again. Therefore, the kiln got too hot for the clay and luckily shut off after 12 hours before burning out all the elements. SO, BE ADVISED, if you ever have a power outage while the kiln is on, let it cool down and use a new cone before starting it again.

  • Katie

    I also have the kiln in my classroom and fire on weekends when there are no kids. While I’m familiar with that horrible popping sound I am very adamant of warning my students of consequences from not following directions when working with clay–not just for their projects but for those surrounding them. I let projects dry for at least a week before firing. It’s helped a lot. Last year i didnt lose anything and only 1 piece the year before that. Like Emily, I have a problem with the kids not attaching things well enough and then popping off despite emphasizing the 4 S’s score, slip, stick, and smooth. Any pointers or tips for this? Thanks for any advice!

    • Cassidy Reinken

      Love the 4 S’s (I only use score and slip) I will have to add the stick and smooth. Thanks for sharing!

      • Lonna

        I use score, slip, smoosh, and smooth to emphasize that the attachment needs to be snugged in there before they smooth.

  • Carrie

    I NEVER fire the kiln when I am not present. So many things can happen, such as the kiln not shutting off, going to too high of a temperature, etc. I do set the timer so that it will start early in the morning (3am) and be at 500 degrees when I come in at 7am then shut off at 3pm.

    I teach 3 high school level ceramics classses who know the consequences of not properly joining clay together, hollow areas that can blow up, and too thick of clay. It seems at the beginning of the year I have more things blow up. I start taking points off towards the end of the 1st grading period, because at that point they should know better.

    With younger kids, I can imagine it would be different, but in my situation my students know better, but sometimes get lazy with craftsmanship and then KABOOM!

  • Emily

    At my first school the kiln was in the teachers workroom. I didn’t like to fire it during the day because so many people were in and out of the room and it would get so hot in there. Plus there was just a little barricade to keep people from touching the kiln. One night while it was firing, somehow a plastic tub was set on top of it! Luckily the night custodians were there and smelled the smoke from the tub burning and melting! Oh my gosh, I felt so bad! I put up lots of warning signs after that, and prayed. The year after I left I heard from the next art teacher that the electrical socket in the wall exploded or something. A cursed kiln for sure.

    • Cassidy Reinken

      Electric kilns are amazing!
      Your story reminded me of when red solo cup melted on the top of my kill- it turned into a beautiful sculpture and serves as a good reminder of how hot the kiln can get, and how fast!

  • Sarah

    Oh man! I’ve been there. Few things can make you feel worse as an art teacher. Thanks for sharing!

  • H. Taylor

    I didn’t know it was called “candling”, but we do this at our site during the winter especially (when it takes FOREVER for clay to dry). I feel for the folks that have to use cones. I’ve been very spoiled with an electric kiln. We still have our occasional explosion, and when that happens, I feel guilty too. I try my best to let the student re-make the piece when they finish other projects early, or during recess/lunch.

  • Kathryn Premraj

    I did use cones (really old kilns), but as I learned from the art teacher before me, I used a small piece of furniture to keep the lid slightly open and put the kiln on low over night, basically a long, low candling. (I am not sure about the safety of this in retrospect, but I took the previous teacher’s advise since he had been there for so very long.) It always worked though, and in two years I had very very little pop! The following day, after it had shut off and cooled, I would then start it on low closed, then ramp it up to medium, then high, when the cone curled and switched off. It was rough though, in an old school basement, coming in my PJ’s with an overcoat and flashlight to manually switch it up!! I would make my husband talk to me on the phone because it was so creepy at night!

    • Cassidy Reinken

      This sounds like what my mom used to do before she retired from teaching art! I’m so thankful I have an automatic kiln.

  • Toby

    I am lucky I have a separate kiln room with clay storage just across from my classroom so I hear nothing or smell nothing. No heat or safety issues. I always make examples as they create….just in case one blows… I save the examples from year to year too for the student who moves in the day we are glazing and has no project….with our tight schedule ( we meet only every eight days) no time to make one… They would get too far behind in the other projects. They just are evaluated on their glazing as they didn’t create it. It helps to make new kids feel part of the group.seems to work.

  • Annemarie

    I have worked in clay since I was 6. I have a MFA with a ceramics major. I have built up a strong component to our art program at the middle school I teach at.
    If something blows up in the kiln, it’s because I didn’t let it dry long enough. When we make any clay project, I usually have students make 2 versions, the second one being better and that way they at least end up with one project to take home.

    My secret to not having things blow up in the kiln is not kosher at all but it works for me. I put all the projects student make ON TOP of the kiln and fire the kiln. The next day I put the thoroughly dried projects in the kiln. Nothing blows up in the kiln ever that way.

  • Lynn

    I have a solution for pieces that pop off before firing. It’s called paper clay and it’s a miracle! You mix 1 part toilet paper with 2 parts slip in a blender. The resulting slip will repair ANYTHING, even at a bone dry stage. I would have a lot more tears in the elementary art room if it wasn’t for the paper clay.

    • Rina_k6art


      That sounds amazing!
      I’ve tried Magic Mender and also vinegar to bone dry clay and it didn’t work. I’ll give yours a try. Now to the thrift store to find a blender!

  • Jen Matott

    I had a WHOLE kiln full of projects blow up last year. I tried to rush them along before the Christmas break… it was awful! I knew they were still a bit moist, put the kiln on low and prayed, but when i opened it, the entire lower level was in a million pieces. The top layers fared better with only a few cracks and missing pieces. I took a photo of the kiln when i opened it and showed the kids what happened (I had already cleaned up the mess, salvaged what could be fixed, and thrown away the rest) and did a lesson on clay and how it dries/ fires. I have taught for 15 years and this was the first time I have blown up a whole load! The kids remade the pieces and all was well. Such a pain! Now, I always fire on low for several hours or all day and then fully fire the next day! Just to be safe!

  • Doris Benter

    This happened with some clay face casts that the children had made. Several “exploded” in the kiln. We turned this “mistake” into a learning opportunity by combining the broken clay pieces into a mixed media seascape (the theme was decided upon by the class after experimenting with the clay pieces). The clay was attached to a painted background (luan) and adhered using liquid nails. We got fabulous results and kids got a lesson in how artists are able to rethink, replan and move into action in art.

  • Jess

    This just happened to my this morning in my art room. i have an extremely talented student who made a clay sculpture for the Beta Club’s convention next week. She worked so hard on it, and I let it dry for 3 weeks in the kiln room. It was maybe a foot tall, and we hollowed out the whole inside. I had taken another load out of the kiln a couple days before this, and so I also let it sit in the kiln for a day when it was barely warm, just to make sure. I opened the kiln this morning, and it exploded into a million little pieces. I didn’t even hear a sound coming from my kiln room! It is so confusing, and I feel extremely guilty over the whole incident. There is no way for her to salvage it by next week. Very frustrating!