SmartsyArtsy Posted September 1, 2014 Report Share Posted September 1, 2014 After 175 ^04 and ^6 firings I had my first incomplete firing. According to the controller info, this small SPS Crucible kiln either had a low voltage issue or problem with the elements. It got to 2166 F before the error aborted the firing. I attempted to do a full on test to examine the elements but will have to come back later when it is dark so I can see the elements more easily. The night after the firing (last night) we had a wide area blackout from some unknown (to me) problems. So, I am wondering if the kiln issue was related to an impending obvious voltage problem. Much to check on. I am also tempted to just do another ^6 firing and see if all is OK now. Meanwhile, I am wondering if the horrific bloating on the one large planter in that firing is the result, and if I should take a chance on re firing it. It went through a slow bisque with good results, but wonder why it bloated so much. The whole piece is bellowed, and there are 30 or so bloats from the size of a marble to a grade a large egg. This is Klamath Brown 634 clay-- first time using it. If I retire, could it explode from the bloats? Link to comment Share on other sites More sharing options...
bciskepottery Posted September 1, 2014 Report Share Posted September 1, 2014 The bloat could be caused by gases in the clay body not escaping because the glaze is sealing over before they escape. don't think a refire will help any; you will likely learn more by breaking the platter on the bloats and seeing how the inside looks . . . just be careful and take normal safety precautions (safety glasses, gloves, etc). Did the bloating only happen with this one glaze, or did other pieces with different glazes also bloat? It could be an incompatibility with the one glaze, if localized to the only piece. Firing a new piece with same glaze will tell you if it is a problem. Link to comment Share on other sites More sharing options...
Mark C. Posted September 1, 2014 Report Share Posted September 1, 2014 The elements may be fine as well as the voltage it could be the pyrometer thermocouple probe going out-it tells the computer what the temp is and has a limited life. I have no idea what the life is in your setup but Neil may if you discribe your setup. May be a relay issue? The blaoting sounds like the brown clay body-just put a new small piece in next fire as your bloated piece is toast it sounds. Mark Link to comment Share on other sites More sharing options...
SmartsyArtsy Posted September 1, 2014 Author Report Share Posted September 1, 2014 I wondered about the clay body/glaze fit, but doesn't that also include the firing error as a factor? Unfortunately, (but really fortunately) there was only one other piece and a few test tiles in there beside the planter. The other piece was fine (except for where the bloated planter kissed it) the test tiles even looked ok. They were just a test for a pattern design of two reliable glazes in my repertoire. So, regardless of the lower temp reached and the free fall cooling, all else was OK. I can and will test fire another piece with the same clay/glaze. The Error says that the heat was climbing less than 12 degrees per hour. sounded like a voltage drop to me, but I would like to understand how to check the thermocouple. Link to comment Share on other sites More sharing options...
SmartsyArtsy Posted October 2, 2014 Author Report Share Posted October 2, 2014 The firing problem was a thermocouple that I needed to replace. For the benefit for anyone else here who has never replaced one, it was a bit more confusing. After the first error msg with dark clay, "Error 1": low voltage or bad elements, I fired a white stoneware bisque load and had no problems. Then I fired a white stoneware light glaze load and had no problems. The third firing after the "Error 1" was another large dark clay planter. That resulted in "FAIL" and another bloated pot. When I went to purchase a new thermocouple, I asked about the bloating dark clay. I was told to fire only to ^5 -- even though it says ^4-^6 Link to comment Share on other sites More sharing options...
neilestrick Posted October 2, 2014 Report Share Posted October 2, 2014 Error 1 is terribly vague. It simply means that it's not heating as fast as it should, which means the problem could be ANYWHERE in the electrical path- wires, connections, relays, elements, etc.- or the thermocouple. You have to go through the system with a meter to find the problem. In your case you were lucky because the thermocouple actually failed, alerting you to the problem. Checking the elements visually to see if they glow will only tell you that there are no breaks in the elements. But they could very well be worn out to the point that they aren't getting hot enough to do the job even though they are glowing. The only way to tell if an element is good is to check the resistance with a meter. That said, if the coils are laying over and bunching up they are probably due for replacement. Voltage drops in the electrical service that are big enough to mess up a firing are very, very rare. I've never seen it happen in 10 years of repairing kilns. You could check a thermocouple with a multi meter that reads millivolts, but it's really not worth the hassle. If everything in the electrical current path is working as it should, then the problem is most likely the thermocouple. A visual check is all you need. If it's corroded, it should be replaced. Link to comment Share on other sites More sharing options...
neilestrick Posted October 2, 2014 Report Share Posted October 2, 2014 Several of the dark commercial clays max out at cone 5. Standard 266 is another example. Link to comment Share on other sites More sharing options...
potterbeth Posted October 3, 2014 Report Share Posted October 3, 2014 I use Standard 266 (dark brown clay body, no grog), bisque to cone 06 and glaze to cone 5. Even then, I will occasionally get a bloated piece, particularly with one glaze. But the beauty of the rest of the work makes the risk worth it. I know of another studio using the same clay body that had horrible bloating problems at cone 5...but they were firing a low bisque at cone 010. Just another factor to consider. Link to comment Share on other sites More sharing options...
SmartsyArtsy Posted October 3, 2014 Author Report Share Posted October 3, 2014 Lessons learned! I had forgotten what the thermocouple first looked like; now I know! Link to comment Share on other sites More sharing options...
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