Tunatown Posted July 11, 2020 Report Share Posted July 11, 2020 Hi Folks, Looking for some expertise about a strange occurrence during glaze firing. My colleague was supervising the kiln through it's final ramp, and texted me to inform me that she heard a "big loud bang" at 2200 degrees. Has anyone heard of a piece exploding during glaze firing, let alone at this temp? She's not a ceramicist so I think it is possible she heard the relays switching and mistook it for an explosion- but that usually isn't something I would qualify as a big bang noise. If it helps, the kiln is electric with a digital controller and I am firing to cone 6. Thoughts? I will learn what actually happened when I open the door, but for now, I am too anxious for words. Thank you! Link to comment Share on other sites More sharing options...
Bill Kielb Posted July 11, 2020 Report Share Posted July 11, 2020 I have only experienced this with some refires that could not tolerate the stress and broke during the upper temperatures of the firing. Link to comment Share on other sites More sharing options...
Tunatown Posted July 11, 2020 Author Report Share Posted July 11, 2020 1 minute ago, Bill Kielb said: I have only experienced this with some refires that could not tolerate the stress and broke during the upper temperatures of the firing. Thanks, Bill. Did you find that glaze splattered onto kiln walls or elements? I am hoping to avoid having to replace anything outside of kiln furniture if it was the case. Link to comment Share on other sites More sharing options...
Bill Kielb Posted July 11, 2020 Report Share Posted July 11, 2020 Just now, Tunatown said: Thanks, Bill. Did you find that glaze splattered onto kiln walls or elements? I am hoping to avoid having to replace anything outside of kiln furniture if it was the case. Unfortunately it popped enough to land in, you guessed it, the bowls! Since then we have a policy, no refires without everyone knowing and when they are tolerated, they go on the bottom shelf. Link to comment Share on other sites More sharing options...
Mark C. Posted July 12, 2020 Report Share Posted July 12, 2020 4th of july fire???? at that temp maybe a cracked piece took out another falling. Hopefull not a shelve collapse-wrong temp for explosions- as a tuna fisherman myself I must ask about your name-Tunatown please tell us how the fire turns out as well Link to comment Share on other sites More sharing options...
Tunatown Posted July 12, 2020 Author Report Share Posted July 12, 2020 37 minutes ago, Mark C. said: 4th of july fire???? at that temp maybe a cracked piece took out another falling. Hopefull not a shelve collapse-wrong temp for explosions- as a tuna fisherman myself I must ask about your name-Tunatown please tell us how the fire turns out as well A fallen shelf crossed my mind but I am really hoping it's not the case! That would be truly tragic. I will surely post an update here in case it proves helpful for anyone in the future. Thank you for your insight! Tunatown came from a couple of sources. My dear furry cat friend/studio assistant is named Tuna. It also happens that fish keeping is a huge passion of mine when I am not making pottery. Alas no fisherman here but rather a huge respect for the species. Link to comment Share on other sites More sharing options...
Tunatown Posted July 12, 2020 Author Report Share Posted July 12, 2020 @Bill Kielb @Mark C. Here's the update! Thankfully not an explosion or shelf collapse. I think it was the sigh of relief heard around the world. What I did find, was that two of my bowls developed some pretty gnarly cracks. They didn't have any cracks during the greenware or bisque phase, and were very even. Curious about what could have caused this. My initial thought was that it didn't fully mature during the bisque fire and still had remnants of moisture. However, my other pieces were completely fine. Could this just be one of those fluke things? This was a different clay body than I have ever used so I am still working out the kinks. Link to comment Share on other sites More sharing options...
Mark C. Posted July 12, 2020 Report Share Posted July 12, 2020 This is where a photo will help us tell you what happened . Link to comment Share on other sites More sharing options...
CactusPots Posted July 12, 2020 Report Share Posted July 12, 2020 19 hours ago, Tunatown said: Alas no fisherman here but rather a huge respect for the species. It's easy to have respect for Thunnus thynnus, when he's kicked your ass and made you cry like a little girl. Personal experience. Link to comment Share on other sites More sharing options...
Tunatown Posted July 12, 2020 Author Report Share Posted July 12, 2020 8 minutes ago, Mark C. said: This is where a photo will help us tell you what happened . Couldn't get the photo of the bowl with a larger crack to attach no matter how much I resized it but here is one of them. Link to comment Share on other sites More sharing options...
Tunatown Posted July 12, 2020 Author Report Share Posted July 12, 2020 3 minutes ago, Tunatown said: Couldn't get the photo of the bowl with a larger crack to attach no matter how much I resized it but here is one of them. Here is the other bowl Link to comment Share on other sites More sharing options...
Babs Posted July 13, 2020 Report Share Posted July 13, 2020 The cracks wouldnt cause the explosive noise. Are the edgges of those cracks smoothed or sharp with clear cut of glaze? Link to comment Share on other sites More sharing options...
Tunatown Posted July 13, 2020 Author Report Share Posted July 13, 2020 @Babs The cracks are very smooth and clean Link to comment Share on other sites More sharing options...
neilestrick Posted July 13, 2020 Report Share Posted July 13, 2020 In the second photo the glaze has pulled back from the crack, which means it probably happened during heating. Cracks that come straight down from the rim like that are usually the result of poor compression of the rim after stretching, or stress during some other part of the process, like during trimming. If the lip is a little bit uneven, the uneven pressure applied to the rim while it's sitting upside down during trimming can cause stress/cracking that isn't visible until glaze firing. Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted July 13, 2020 Report Share Posted July 13, 2020 The yellow one looks like it was picked up by the rim one handed while it was green. That can sometimes cause micro cracks that aren’t visible after the bisque. The only way to find them is to flick the bisqued piece to see if it rings. Link to comment Share on other sites More sharing options...
Tunatown Posted July 14, 2020 Author Report Share Posted July 14, 2020 On 7/13/2020 at 4:20 PM, neilestrick said: In the second photo the glaze has pulled back from the crack, which means it probably happened during heating. Cracks that come straight down from the rim like that are usually the result of poor compression of the rim after stretching, or stress during some other part of the process, like during trimming. If the lip is a little bit uneven, the uneven pressure applied to the rim while it's sitting upside down during trimming can cause stress/cracking that isn't visible until glaze firing. That makes perfect sense as the cause for the cracking. Thank you! Link to comment Share on other sites More sharing options...
Tunatown Posted July 14, 2020 Author Report Share Posted July 14, 2020 On 7/13/2020 at 4:53 PM, Callie Beller Diesel said: The yellow one looks like it was picked up by the rim one handed while it was green. That can sometimes cause micro cracks that aren’t visible after the bisque. The only way to find them is to flick the bisqued piece to see if it rings. Thanks, Callie! I have never heard of that trick and I will definitely try that in the future. Grateful for everyone's expertise here! Link to comment Share on other sites More sharing options...
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