Lbauer12 Posted March 22 Report Share Posted March 22 I have a Duncan the teacher manual kiln that fires pretty fast: 5-6 hours for cone 05. I figured the problem was that it was firing too fast, I slowed it down as much as possible but it came out with even more pinholes, even bigger, like craters. I let it cool about 20 hours before taking it from the kiln. I read that too much glaze can be a problem, which I might have put on too much. I also read firing to 04 could help. I bisque fired to 04, but again it only took 5-6 hours. Any bets on what the issue is? There are so many variables to adjust I don’t know where to start. Thanks. Quote Link to comment Share on other sites More sharing options...
Min Posted March 22 Report Share Posted March 22 Just to clarify you are firing lowfire glaze to cone 05 on a lowfire body that has been bisque fired to cone 04? Or cone 6 glazes on cone 05 and 04 bisque? How fast are you ramping up the kiln for both bisque and glaze? Is it possible to do a hold/soak with this kiln? Are the glazes your recipes or commercial ones? If they are your recipes could you post a recipe or two that are giving you problems? What claybody are you using? Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted March 23 Author Report Share Posted March 23 (edited) I’m using Sheffield mass red, I think it’s 03-05. I am using 05 Amaco Artists choice and Amaco opalescent combinations. 2 coats of opalescent under 1 coat of Artists choice. About half of them came out fine, the last several batches I’ve fired have gotten worse to the point that it’s not just pinholes it’s more like big pits. I try to fire as slow as I can and it averages 5-6 hours. This is a manual kiln so no way to do a soak or hold. I bisque to 04, I make sure there is no water vapor coming from the peephole for awhile before closing it. But again it’s 5-6 hours. The Artists Choice are out of production, I just ordered them but maybe that’s part of the problem. I also have Mayco Elements that I also got some pinholes with but overall less issues. There is also a lot of pinging going on so I know there are crazing issues as well. There are just so many variables I don’t know where to start, other than to buy a new kiln. Edited March 23 by Lbauer12 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 23 Report Share Posted March 23 On 3/22/2024 at 9:32 AM, Lbauer12 said: I have a Duncan the teacher manual kiln that fires pretty fast: 5-6 hours for cone 05. I figured the problem was that it was firing too fast, I slowed it down as much as possible What is your firing schedule? Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted March 23 Author Report Share Posted March 23 What’s a firing schedule? I have this set to auto low, turn the infinite switch to about 10:00 let it go 2 hours with peep holes open, turn to 8:00, shut bottom peep, then 6:00 with both closed until it shuts off. Quote Link to comment Share on other sites More sharing options...
Min Posted March 23 Report Share Posted March 23 I looked up the Mass Red clay from Sheffield Pottery, from their info it fires from 06 up to 02. I don't use commercial glazes so I also looked up the glazes you are using, Mayco Elements have a range from ^06 up to ^6 and the opalescent are ^05 if you go at 270F and hour for the final 200F of firing and the Artist's Choice recommend ^05. All claybodies are strongest when fired to their top maturity temp/cone. So for your body the clay needs a higher bisque than what your glazes fire to. This is okay for earthenware as the body will still be porous enough to accept the glaze well. I would suggest bisque firing to ^02 and turning the dial up very slowly. Don't rush when you turn it up! Leave peeps open to get air through the kiln, it helps burn off impurities in the clay. I would suggest leaving all the peepholes open until you see the kiln glowing red inside then shut the bottom one and leave the top one open for the entire firing. Once the kiln stops then you can close the top one off. (I'm assuming it has 2 peepholes?) For the glaze firing, again you want to slow it down, doesn't have to go as slow as the bisque though. I'm not familiar with your kiln but what you are trying to do is slow down the firing, Try and stretch out the middle and then particularly the end of the firing. Someone more familiar with your kiln than I am should be able to help you with this part. Given that the clay has already reached it's maturity with the bisque firing then the glaze firing is to get the best looking glazes you can. Cone 05 should do it although the Mayco Elements can go higher, if you have a hotter area in your kiln you could try putting those glazes there. When I looked at some images of Mayco Elements I do see a fair number of pinholes in one of them when fired to ^06 so the odd one might be more prone to pinholes. (image below from Mayco's website of Oyster Shell) Hulk 1 Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted March 23 Author Report Share Posted March 23 Thanks, I’ll try 03 next time since I don’t have 02 sitter cones. Oyster shell was one of the glazes I had issues with pinholes. Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 23 Report Share Posted March 23 (edited) 3 hours ago, Lbauer12 said: What’s a firing schedule? I have this set to auto low, turn the infinite switch to about 10:00 let it go 2 hours with peep holes open, turn to 8:00, shut bottom peep, then 6:00 with both closed until it shuts off. While Fast glazing may / may not be a problem, fast bisque generally not the greatest practice unless you know your clay has burned everything out in that timeframe. To slow things down modify your turn up schedule leave it on low for longer or turn it up less. Duncan provides calibration instructions for the switch. It may be too old to calibrate but following the analysis part should reveal if it is just too worn and needs to be replaced. For now, just as a test, I would slow down the bisque simply by firing slower, more in the 8-12 hour range for sure to see the effect on your clay and glaze. If you leave it at the 10:00 position and do not turn it up, how long to 04? If that extends the firing, then calibrated or not calibrated you have an option to slow things down to test with. Edited March 23 by Bill Kielb Hulk 1 Quote Link to comment Share on other sites More sharing options...
Babs Posted March 23 Report Share Posted March 23 Looks like from Min's post that tge pinholes whete thicker in the texture indens. Maybe you're applying too thick also. C 03 bisque would say to mre that you wont be able to glaze too thickly :-)) Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted March 24 Author Report Share Posted March 24 Ok, are you saying if I bisque to 03 then applying glaze too thick will show up as even more of a problem? Should I just bisque to 04 and try to extend as much as possible by leaving it on low at the 10:00 position? Should I leave both the peepholes open the whole firing to extend it? Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 24 Report Share Posted March 24 24 minutes ago, Lbauer12 said: Should I just bisque to 04 and try to extend as much as possible by leaving it on low at the 10:00 position? Should I leave both the peepholes open the whole firing to extend it? If you leave it on 10 with your normal peep hole procedure, how long does it take to get to 03, or 04? Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted March 24 Author Report Share Posted March 24 I’ve never just left it at 10 before, so idk how long that would take. Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 24 Report Share Posted March 24 (edited) 56 minutes ago, Lbauer12 said: so idk how long that would take. Maybe time to test it out? Edited March 24 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted March 24 Author Report Share Posted March 24 Do 04 or go to 03? Which will be more likely to reduce defects? Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 24 Report Share Posted March 24 (edited) 15 minutes ago, Lbauer12 said: Do 04 or go to 03? Which will be more likely to reduce defects? How about an empty firing to 04 just to see how long it takes to get there with the dial set at 10 and never turning up? Maybe make sure you can make it in ten to twelve hours? It’s just getting to know how your kiln fires so you can apply it as needed. Edited March 24 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
Babs Posted March 24 Report Share Posted March 24 My point was, given Min's info on clay, at a bisque to C03, your clay would be not very porous do would not take up much glaze if dipped, Quote Link to comment Share on other sites More sharing options...
Min Posted March 24 Report Share Posted March 24 11 minutes ago, Babs said: My point was, given Min's info on clay, at a bisque to C03, your clay would be not very porous do would not take up much glaze if dipped, Approx 6.5% at cone 06. I would do a test firing to cone 03 and include some test tiles. Just like the kiln firing it’s going to take some testing to see how the glazing. I’m not a big fan of underfiring clay bodies. I couldn’t find any data on absorption figures for anything other than 06, would be something I would test. Quote Link to comment Share on other sites More sharing options...
Babs Posted March 24 Report Share Posted March 24 24 minutes ago, Min said: Approx 6.5% at cone 06. I would do a test firing to cone 03 and include some test tiles. Just like the kiln firing it’s going to take some testing to see how the glazing. I’m not a big fan of underfiring clay bodies. I couldn’t find any data on absorption figures for anything other than 06, would be something I would test. Ok, if clay is rated to cone02, then a subsequent glaze and fire to C06 to suit the glazes could mean a difficult beast to get a layer of glaze to adhere to? Don't know the glazes or the clay or tge method of glazes so assumption on my part, sorry. Quote Link to comment Share on other sites More sharing options...
Min Posted March 24 Report Share Posted March 24 I think that since so many of us fire to midrange the go to mindset is bisque low, fire higher to glaze. Problem with this when working with earthenware is more often than not the commercial glazes are rated in the 06-04 range yet many earthenware bodies will actually mature higher than this and still be porous enough to take glaze well. I haven't used the body in question, but if it can go to 02 (as the lit suggests) then I would at least try 03 and see how it does. Babs and Callie Beller Diesel 2 Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted March 29 Author Report Share Posted March 29 I did an 04 test firing with the dial at 10:00 the whole time. I put covered the bottom peephole 5 hours in. After 10 hours I cranked it up because I wanted to go to bed. Will firing 10-12 hours instead of 5-6 help eliminate pinholes and crazing? For a glaze fire would it be best to do the same thing? Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 29 Report Share Posted March 29 (edited) 7 hours ago, Lbauer12 said: Will firing 10-12 hours instead of 5-6 help eliminate pinholes and crazing? Crazing is a clay and glaze expansion mismatch issue. In general it’s usually related to the match between clay and glaze and probably rarely related to bisque temperatures so I don’t want to confuse two issues here. As far as pinholes, yes effective bisque may help with pinholes. If all the organics are not burned out in the bisque, they can create a pinhole issue as they burnout in the glaze firing. Effective burnout of organics depends upon time AND time at temperature. Most bisque cycles run 10-12 hours to try and ensure all organics are removed. So now I think you know that you can fire slower and when you have reason, modify your turn up schedule as appropriate. Originally I think you felt that it was firing as slow as possible ……. Hopefully now you have a way to go as slow as you find necessary, bisque and glaze. Edited March 29 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted March 29 Author Report Share Posted March 29 Hopefully that will help. I don’t feel like I was glazing too heavily(3-4 coats brushed). Or cooling down too fast(20-24 hours). Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted March 29 Author Report Share Posted March 29 I have some stoneware I previously fired in 5-6 hours at 04 to bisque. Would it be ok to re-fire it at 10-12 hours? Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 30 Report Share Posted March 30 6 hours ago, Lbauer12 said: Would it be ok to re-fire it at 10-12 hours? Yep! It will likely tighten somewhat so a nice 10 hr bisque to 05 / 06 might be just the thing. Time at temperature is important to complete burnout. You might be able to work out a slower turn up schedule so it’s not such a guess each time. So turn up to ten, then maybe 1-2 hours nine / eight …… a cheap pyrometer can help a bunch here. Anyway, a way to slow things down and for bisque a way to try and burn everything out that could cause problems by going slowly. All part of testing and learning kiln, clay, glaze….. Quote Link to comment Share on other sites More sharing options...
Lbauer12 Posted April 4 Author Report Share Posted April 4 I have one more question. My kiln is in my garage. Is it ok to fire when it’s around 40 degrees outside. The thing I’d be concerned about is when I take it out if the change in temperature would damage the glaze. If I wait until it’s room temperature does it matter if it’s a little cold? Quote Link to comment Share on other sites More sharing options...
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