2Relaxed Posted October 24, 2020 Report Share Posted October 24, 2020 I emailed Skutt support but thought I'd post it here, too, to share what I find out from them and hopefully get some advice as well. I have bought a used KM 1018-3 kiln almost 2 years ago. It was around 25 years old at the time. I have immediately replaced all elements and the thermocouple. Did a test firing per instructions. Ever since I've only had a handful of bisque and cone 6 firings (I'm slow and make pots only in my spare time - mostly weekends) and it seems that this kiln has been slightly overfiring from the beginning. Lately I feel that this problem is becoming worse. The latest bisque fire took almost an hour longer than the previous one with the same schedule and a similar load. My witness cones bent more than the ones in the previous firing. I use the ^04 bisque schedule from this article, just with no holds (all my wares are bone dry when loaded into the kiln): https://www.aardvarkclay.com/pdf/technical/Bisquefiring.pdf I usually use this cone 6 schedule for glaze fires: https://digitalfire.com/schedule/plc6ds Latest firing melted both ^5 and ^6 self-supporting cones to the point that they were touching the shelf. I would like to get some advice on what steps I can take to diagnose this problem and then correct it. I have a glaze firing coming up and don't want to lose my work to overfired glazes. Thank you! The pic below is of ^04 (middle) and ^05 (edge) from my latest bisque fire. I also forgot to mention that I vent the kiln throughout the entire firing. Link to comment Share on other sites More sharing options...
Min Posted October 24, 2020 Report Share Posted October 24, 2020 It sometimes takes a couple firings to get the peak temperature dialled in to correlate with how you want your cones to bend. If the schedule you linked to is running about 1/2 to 1 cone too high/hot then drop the peak from 2200 down to around 2185 then do the 10 minute hold. If you are comfortable looking at the cones (using kiln glasses) then look at them through the peephole as you are approaching 2185 and again after the soak. Add or decrease soak time if necessary, have to do this quickly so the temp doesn't drop like a stone. If you aren't comfortable checking the cones as the kiln is firing it's going to take a couple firings to get it sorted. Link to comment Share on other sites More sharing options...
2Relaxed Posted October 25, 2020 Author Report Share Posted October 25, 2020 Min, so you are saying I only need to adjust the peak temperature to stop the cones from bending too much? May I am really overthinking it suspecting that something is wrong with the kiln.. Link to comment Share on other sites More sharing options...
neilestrick Posted October 25, 2020 Report Share Posted October 25, 2020 Kilns don't always fire accurately. It's not at all uncommon to have to make adjustments to dial it in. However based on your descriptions and photos, I'd say it's not over-firing much at all. How do your glazes look? Do you have a pic of the cone 6 cone? Link to comment Share on other sites More sharing options...
Bill Kielb Posted October 25, 2020 Report Share Posted October 25, 2020 Those cones are not overly bent actually so depending on placement etc..... it does not appear to be a significant variance from desired temperature / time. The 04 looks like it has collided with the holder. The bisque schedule you linked is interesting in that it finishes in 26 hours but has a twelve hour hold at 180 degrees. Interesting but excessive for most ordinary pottery. Both schedules seize on the idea that in about the last 200f degrees of the firing to follow 108 degrees per hour as in the center column of the Orton chart. Cones are made of glaze so in theory when they act appropriately we have fired to a certain amount of heatwork (heat for a given amount of time). Changing any of the time or temperature values in the last segment will fine tune this. So for instance by dropping the top temperature a few degrees per trial you will reduce your heatwork. Changing more than one thing for instance, time and temperature will also have the same effect but the more things you vary simultaneously the more random your results can be. Many do it successfully intuitively after years of experience and of course trial and error. Link to comment Share on other sites More sharing options...
Sorcery Posted October 25, 2020 Report Share Posted October 25, 2020 Do you have a kiln sitter? What are you using to operate it? If using the cones, moving them slightly in either direction raises or lowers the firing time. This could be why it takes longer, or you could have packed it fuller, or you could have one too many peeps open, or....it's not likely the kiln. Sorce Link to comment Share on other sites More sharing options...
2Relaxed Posted October 25, 2020 Author Report Share Posted October 25, 2020 15 hours ago, neilestrick said: Kilns don't always fire accurately. It's not at all uncommon to have to make adjustments to dial it in. However based on your descriptions and photos, I'd say it's not over-firing much at all. How do your glazes look? Do you have a pic of the cone 6 cone? Here it is, ^5 on the left, ^6 on the right. Link to comment Share on other sites More sharing options...
2Relaxed Posted October 25, 2020 Author Report Share Posted October 25, 2020 @Bill Kielb Since I don't use any holds in bisque fire, it ends up taking about 13-14 hours. Link to comment Share on other sites More sharing options...
2Relaxed Posted October 25, 2020 Author Report Share Posted October 25, 2020 @Sorcery It's a computerized controller on my kiln and I use ramp/hold manually entered schedules. The only cones are witness cones. Link to comment Share on other sites More sharing options...
Min Posted October 25, 2020 Report Share Posted October 25, 2020 If you are aiming for ^6 that cone is spot on. You are only talking a couple degrees between the tip being exactly at the same level as the top of the self supporting base. I'm not seeing a problem with the cone. Do your glazes look okay? Link to comment Share on other sites More sharing options...
Bill Kielb Posted October 25, 2020 Report Share Posted October 25, 2020 2 hours ago, 2Relaxed said: Here it is, ^5 on the left, ^6 on the right. Looks really good for cone six, your cone 04 looked pretty good. Do you have an issue with either? Link to comment Share on other sites More sharing options...
Mark C. Posted October 25, 2020 Report Share Posted October 25, 2020 That cone 6 is picture perfect . the tip is equal to the base-meaniong a perfect end point.The cones is more important than some computer theoretical temp. That cone is cone 6 spot on. What matters more than that (and its why everyone is asking ) how do the glazes look at that perfect cone 6.?? Are they great? or do they need some soak time added???? To flux them out more?Even though you have a cone 6 perfect the glazes can still need some soak time. Link to comment Share on other sites More sharing options...
2Relaxed Posted October 25, 2020 Author Report Share Posted October 25, 2020 Ok guys, you have convinced me that I'm overreacting or just being paranoid Next glaze fire better be good! Link to comment Share on other sites More sharing options...
Bill Kielb Posted October 25, 2020 Report Share Posted October 25, 2020 As is often said by many potters, many times it is not the kilns fault Link to comment Share on other sites More sharing options...
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