Lbegley Posted November 16, 2018 Report Share Posted November 16, 2018 I fired a cone 10 gas kiln yesterday and the cone 10 and cone 11 melted at exactly the same time, on both the bottom and top cone packs. I’ve never seen this happen. Does anyone know what would cause this? Link to comment Share on other sites More sharing options...
Mark C. Posted November 16, 2018 Report Share Posted November 16, 2018 Yes I have seen this happen many times-it means your kiln is flying fast temp wise-both cones start falling as the climb is moving upwards fast. The other reason is the kiln can be slow moving(super saturated at a given temp) and then a small adjustment can make the temp fly fast. Either way cones can fall together. Link to comment Share on other sites More sharing options...
neilestrick Posted November 16, 2018 Report Share Posted November 16, 2018 Cones 10 and 11 are only bout 18 degrees apart at a climb of 108F/hr, so they'll often drop together. Link to comment Share on other sites More sharing options...
Bill Kielb Posted November 16, 2018 Report Share Posted November 16, 2018 I agree with Neil and add that your kiln has significant thermal mass so the cones may simply reflect stored heat work in the kiln. Most automatic kiln controllers default to between 80 and 120 degrees per hour for the final 250 degrees of firing. This is done so the controller has sufficient time to figure out the actual remaining heat work before shutting off the kiln. Cones contain flux and are intended to reflect vitrification of a fluxed body. Their temperature spreads are not uniform nor do the fall at one specific temperature. They are affected greatly by the rate during the last hour or two of firing. Cones are actually glazes several cones under their rating so they fall when expected to. More importantly, how did you like your results! Link to comment Share on other sites More sharing options...
Mark C. Posted November 16, 2018 Report Share Posted November 16, 2018 Happens all the time-I fire every other week and picked these cone 10-and 11 packs out from some recent fires Do yours look like these cone 10/11 packs????? Link to comment Share on other sites More sharing options...
Lbegley Posted November 17, 2018 Author Report Share Posted November 17, 2018 Thank you for the good information! I did speed up the firing faster than typical towards the end because I needed to shut her down and get out of the studio. That must have been it. I’ll open the kiln tomorrow and see the results. Fingers crossed it’s not overfired!! Link to comment Share on other sites More sharing options...
neilestrick Posted November 17, 2018 Report Share Posted November 17, 2018 18 hours ago, Bill Kielb said: Most automatic kiln controllers default to between 80 and 120 degrees per hour for the final 250 degrees of firing. Unless you're firing fast. On the Dynatrol/V6-CF, they use 200 per hour for the final segment. Link to comment Share on other sites More sharing options...
Bill Kielb Posted November 17, 2018 Report Share Posted November 17, 2018 Yes, Same on the new Genesis which offers a medium speed as well. 120 on slow and medium and they stuck with the 200 on fast Link to comment Share on other sites More sharing options...
Mark C. Posted November 17, 2018 Report Share Posted November 17, 2018 Its best for most glaze to fire slow at the end during the melt process-fast going up is fine slow at the end. Link to comment Share on other sites More sharing options...
Lbegley Posted November 17, 2018 Author Report Share Posted November 17, 2018 Here are the cone packs. The 11 looks more melted than the 10 to me in the front one. Weird! the glazes all look great, so that’s what matters most, but I’m pretty new to firing a gas kiln and need all knowledge I can get out of each firing. The biggest challenge is this is mostly beginning student work, and they sometimes glaze crazy thick, and one of the studio glazes runs like hell when it gets any past 10, so I have a pretty narrow window Link to comment Share on other sites More sharing options...
Bill Kielb Posted November 17, 2018 Report Share Posted November 17, 2018 Pretty interesting, slow at the end is likely best. Angle may have influenced these ever so slightly but the rear cone pack in the picture looks like 10 is at least ahead of 11. Glad your results are fine. We like to keep our firings tight in the community kiln more so because some clay bodies begin to expand beyond their rating. The firing curves on some clay bodies are quite sharp and begin to fall off the planet one or two cones over, Thanks for the picture and good outcome Link to comment Share on other sites More sharing options...
Lbegley Posted November 17, 2018 Author Report Share Posted November 17, 2018 Aside from just me being impatient, this kiln is a little tricky to get to fire evenly top to bottom, so sometimes when it’s ahead on the bottom, I need to open the damper to even it out, but that means speeding up the firing too. I guess the good news is that it was fine, but next time I’ll be sure to make the adjustments earlier and go slower. Link to comment Share on other sites More sharing options...
Lbegley Posted November 17, 2018 Author Report Share Posted November 17, 2018 Luckily in this studio, students are supposed to only use the clay bodies we provide, and they all seem pretty forgiving. The glazes, less so, and I hope to work on that. I’m new to the job, so hopefully I’ll just get really good at hitting the window, but maybe adjusting our problem glaze could help too. Link to comment Share on other sites More sharing options...
neilestrick Posted November 17, 2018 Report Share Posted November 17, 2018 Does the kiln have a bag wall? If so, raising it slightly can help keep the heat up top. If not, you can also try increasing the length of the flame by reducing the air or turning up the gas. Link to comment Share on other sites More sharing options...
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