pattersp Posted January 22, 2021 Report Share Posted January 22, 2021 Hello! I’m new to the world of kilns, so I apologize for the newbie question! I did a bisque firing yesterday to 04. My kiln is an automatic, but I used a self supporting witness cone to see if my thermocouples are calibrated. I should have used a cone pack with 05 04 and 03, but my local clay supply company was sold out of many of the witness cones, so I only could purchase 04. I’m trying to interpret my cone result by searching the web, but I’m getting conflicting info. I’m attaching a photo. Should my witness cone “kiss” the ground, or should it just bend most of the way? Different sources are telling me different things.. please help me learn! Link to comment Share on other sites More sharing options...
liambesaw Posted January 22, 2021 Report Share Posted January 22, 2021 The tip should be on the same horizontal plane as where the base of the cone meets the cone itself. Or about a hemisphere. That cone indicates a slight overfiring, of maybe a few minutes of heatwork. Link to comment Share on other sites More sharing options...
pattersp Posted January 22, 2021 Author Report Share Posted January 22, 2021 Thanks for that info, that’s very helpful. I’ll adjust the thermocouple offset. How many degrees do you think I should add? Link to comment Share on other sites More sharing options...
liambesaw Posted January 22, 2021 Report Share Posted January 22, 2021 Maybe 10? Maybe none. Depends on where the cone was in the kiln and how dense it was. If it was right next to the thermocouple you can mess with it, but I'd be happy with that for now, at least until you can do a full 3 shelf firing with cone packs on each shelf. Another issue with TC offset is that your cone 04 firing might be hot but your cone 6 slightly cool, so if you adjust the TC offset it'll make your cone 6 even less hot, and it's much better to use the cone offset instead. And only after a few firings so you can average the results. Link to comment Share on other sites More sharing options...
Bill Kielb Posted January 22, 2021 Report Share Posted January 22, 2021 9 hours ago, pattersp said: Thanks for that info, that’s very helpful. I’ll adjust the thermocouple offset. How many degrees do you think I should add? You may find this is an extremely small amount and depending how the cone was placed or the wear and tear on your elements the word slightly over fired comes to my mind. If any offset I added affected the glaze fire adversely, I would not add anything. Folks get caught up in perfect cones, but perfect cones are hard to come by in all locations of a kiln. A cone bent to three o’clock is within a couple degrees of being fully bent. So extrapolating at 100 degrees per hour final segment is about 1.6 degrees per minute so a three o’clock cone needed 1 to 3 minutes extra firing. All good theory but much too precise really. Take a look at the chart below to get an idea of just how sensitive this is and glaze fire for your best melt, look, vitrification. Bisque firing to that perfect cone probably not as important especially if we are reasonably thinking about this. Also realize that as your elements wear they will not be able to keep a good final segment rate and this will start to happen both in bisque and glaze. If this cone can directly “see” an element and happens to be fairly close, that may influence the bend slightly. Lots of reasons, but if a guard cone was used in the traditional guide-fire-guard arrangement or cone 03 cone was installed as the guard it likely would have barely bent which would make us all feel this was a good cone 04 firing. Link to comment Share on other sites More sharing options...
irenepots Posted January 23, 2021 Report Share Posted January 23, 2021 Bill, thanks for that graphic! I printed it out. Irene Link to comment Share on other sites More sharing options...
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