suz davis Posted August 10, 2022 Report Share Posted August 10, 2022 hello : ) i have a 43 year old manual kiln. my kiln seems to be underfiring. when i bisque fire to 06, my sitter cone looks perfect at 90°. however, my witness cones tell a different story. the 07 cone looks correctly bent. the 06 cone is at 45°. the 05 cone has only changed in color with no bending. since it appeared to be underfiring, i adjusted my kiln sitter. bisque fired again with similar results. so i decided to put an 05 cone in the sitter in hopes that the witness cones; 05, 06, 07; would bend correctly, aiming for cone 06. the results showed the 07 and 06 cones almost completely bent and melted, with the 05 cone changed in color and slightly bent. the 05 sitter cone was almost over fired, i think. still with me? my question is, wouldn't the 05 witness cone be more bent since i used a 05 sitter cone? i've attached a couple of photos: thanks for your time! Quote Link to comment Share on other sites More sharing options...
Pres Posted August 10, 2022 Report Share Posted August 10, 2022 Suz, I would look up the orton cone chart, and compare the temps for the self supporting and small cones. I believe you will find the small cones fire hotter than the self supporting. At the same time, check carefully to see that your drop rod of the setter is in the center of the small cones length. You pictures are helpful, but I can't figure on which set of cones you are showing as you mention 3 different firings. best, Pres Quote Link to comment Share on other sites More sharing options...
suz davis Posted August 10, 2022 Author Report Share Posted August 10, 2022 hi pres, thank you! i did a bit of research and you are correct. the firing temps of self supporting and small cones are different. the pictures show my latest firing. i used an 05 small cone in the sitter. and 05, 06, 07 self supporting witness cones. my goal was to get a true cone 06. i'm wondering why the cone 05 witness cone didn't bend, since i used a small 05, but the 06 witness cone was over. is my kiln firing almost 1 cone lower? how would i correct that? i have got myself confused i think. it does show that i didn't have the sitter cone properly placed. thank you again! suz Quote Link to comment Share on other sites More sharing options...
PeterH Posted August 10, 2022 Report Share Posted August 10, 2022 1 hour ago, Pres said: Suz, I would look up the orton cone chart, and compare the temps for the self supporting and small cones. I believe you will find the small cones fire hotter than the self supporting. 5 minutes ago, suz davis said: i did a bit of research and you are correct. the firing temps of self supporting and small cones are different. Can somebody point me to an Orton chart which shows the temps for small and self-supporting cones when fired at the same rate? PS The first chart I found gives the (different) cone temps for small cones at a significantly higher firing rate for the small cones. ... this page, while referencing the same Orton charts, implies that small and self-supporting cones operate at the same temps (when heated at the same rate).https://nmclay.com/informational-pages/orton-cone-chart-in-centegrade ... but gives no Orton reference for this Quote Link to comment Share on other sites More sharing options...
Min Posted August 10, 2022 Report Share Posted August 10, 2022 Where in the kiln were the self supporting cones placed? How large is your kiln? Difference in melting of the cones could simply be due to thermal lag if all were on the same shelf but the 07 cone was towards the middle of the shelf, or uneven kiln temps if cones were placed in the same position but on different shelves. Pres and Babs 2 Quote Link to comment Share on other sites More sharing options...
Hulk Posted August 10, 2022 Report Share Posted August 10, 2022 The small cones "...bend about 9 F hotter than the big ones." Orton has corrected the online doc that contradicted this - there's detailed reference archived in this forum somewhere*... My experience has been to place a small cone six in the sitter to get cone five witness cone to bend. That said, witness cones are the way to go, and a pyrometer is super helpful - once the relationship between pyrometer readings and witness cone results are established, it gets easier, but stay on top of it as your pyrometer may drift with time and wear. I would not want to rely on the kiln sitter for accurate heat work; I'm sure it can be done, but why? If starting over, I'd place cone packs where they can be seen (eye protection vitally important, against harmful rays and Any Flying Bits) and stop firing once target has been achieved, noting pyrometer readings. Once repeatability has been established, viewing the cone packs during firing not as important. The sitter/timer mechanism is a failsafe, imho, in case I fall asleep or somewhat, the kiln will eventually shut down on its own. Within the next several years, I do expect/hope to start over, with a new kiln, numerically controlled. The new kiln will come with its own thermocouples, and so, since I would not want to ruin several loads whilst learning, I'll go back to watching cone packs and taking notes during firing, eh? *aha!Kiln Sitter cone for witness cone - Studio Operations and Making Work - Ceramic Arts Daily Community Maybe start at the bottom and read up... PeterH and Pres 2 Quote Link to comment Share on other sites More sharing options...
suz davis Posted August 10, 2022 Author Report Share Posted August 10, 2022 min: thanks for your reply! my kiln has about 3 cubic ft of space. i had two sets of cones on different shelves; one set towards the back, and one set in front of the peep. they ended up with the same deformation. Quote Link to comment Share on other sites More sharing options...
suz davis Posted August 10, 2022 Author Report Share Posted August 10, 2022 hulk, thank you!! i really appreciate your response. lots of info - i have so much to learn! Hulk 1 Quote Link to comment Share on other sites More sharing options...
Min Posted August 11, 2022 Report Share Posted August 11, 2022 (edited) Can you get sitter bars? They tend to be easier to get repeatable results from than the small cones, Other thing you could try is put the cone in so that it’s not cantered under the rod but more towards the wide end of the cone to fire hotter and the opposite to fire cooler. Edited August 11, 2022 by Min Quote Link to comment Share on other sites More sharing options...
Babs Posted August 11, 2022 Report Share Posted August 11, 2022 Kiln 43ys old, wht is the sitter rod looking like? Thin, pointy, sitter needs recalibrating? Rod needs replacing? Min 1 Quote Link to comment Share on other sites More sharing options...
suz davis Posted August 11, 2022 Author Report Share Posted August 11, 2022 thanks min, i'll give it go! hi babs! the rod looks amazing for its age. not thin or pointy. i recently recalibrated the sitter...it might need another adjustment though. thank you for your suggestions! suz : ) Quote Link to comment Share on other sites More sharing options...
suz davis Posted August 12, 2022 Author Report Share Posted August 12, 2022 rockhopper, i honestly don't know. what is the correct placement for the sitter cone? Quote Link to comment Share on other sites More sharing options...
neilestrick Posted August 12, 2022 Report Share Posted August 12, 2022 51 minutes ago, Rockhopper said: Is it just the camera angle - or was the sitter cone placed with a flat side up ( \/ rather than /\ ) ? I think you're right. @suz davis The cone should sit on the support bars with the flat side down, with the number facing toward the inside of the kiln. The cone will bend against the spine, not along the flat side. If it's loaded with the flat side facing up, it will bend easier and shut off early. Quote Link to comment Share on other sites More sharing options...
suz davis Posted August 12, 2022 Author Report Share Posted August 12, 2022 @neilestrick @Rockhopper thank you both!! i have just been putting the cone in the sitter without paying much attention to its position. if you don't know, now you know. thank you again! Pres and neilestrick 2 Quote Link to comment Share on other sites More sharing options...
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