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Showing results for tags 'pinhole'.
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Took some pots out of the kiln and noted pinholes in both the celadon (Amaco Sky) and satin matte (Amaco white) vases. This is one of my earliest glaze firings and I am curious as to the factors to investigate to better control this issue. Here is some data: 1. Both clay bodies are Sheffield 20231G clay 2. Bisque fired in my E23S L&L kiln (programmable) to Cone 06 (verified with actual cones as accurate). 3. These 2 examples were more than a year old before the glazes were applied. Wiped pots but NOT with damp sponge. Possible problem? 4. Applied 3 coats of brushed on Cone 5/6 glazes from Amaco; Sky Celadon and White Satin Matte (examples). Amaco Shino glazes also, but NO pinholes in any of those 4 pieces. I think each coat dried before next coat applied, but not sure how dry is 'enough' (possible problem). I never measured thickness of final glazed product so can't confirm if too thick. Possible problem? 5. These 2 examples were both then fired with other pieces on the top shelf (only 2 shelves) to the pre-programmed Slow Glaze Cone 5. The temperature reached was a little higher than the program 2165F (Actual 2171). Total time 8 hr 44 min (included 15 min pre-heat, NO hold time or custom cool down). Witness cones on both shelves show that witness cone 6 had begun to bend. (I will try to attach a pic). 6. Pinholes seemed to be biggest issue although I also saw some cracking with the celadon glaze. I will try to attach pix. 7 (new). Took pix from top view to see thickness. Also, both of the vases were inner glazed with Amaco Clear glaze. Based on this info (or other you might request), can someone please offer some possible root causes and ways to correct them? I am happy to provide any info that can help you help me. Thank you to any and all comments/advice.
Hello helpful potters! I need help with an 04 bisque firing schedule. I'm having problems with pinholing in the 266 Standard Ceramic cone 4-6 dark brown clay that I'm using. About 50% of the time I'm getting a few pinholes, generally on the bottom but also on the sides. When I slow glaze, my cone 5 witnesses goes all the way down and the 6s are at about 2:00. The glaze I'm using is Potters Choice for cone 5/6, 3 coats as suggested by Amaco Brent, and this problem is happening pretty much just on the 266 and not the lighter color clays I use. I know pinholing can be a symptom of a variety of things, but I'm ready to try a slower bisque schedule in case they're being caused by gases or other impurities that haven't completely burned out during the bisque. Maybe it should go faster to 1100 and then slower for the next 1000 degrees? Or have a hold in there somewhere? I've tried to work out a schedule myself but it always ends up being about 18 hours long. Here's the cone 04 preset firing schedule I'm using in my LL kiln: 80 per hour to 250 (2 hrs) 200 per hour to 1100 (4 hours) 100 per hour to 1100 (1 hour) 180 per hour to 1676 (3 hours) 80 per hour to 1926 I also add a 10 minute hold at the end. When I use this cycle it tells me the end temp will be 1945 instead of 1926, ( 1926 is what it says on this firing schedule. It does end up at around 1945. I unplug the vent when it's done firing. Any ideas will be greatly appreciated, as would any suggestions about other things I may be doing, or not doing, that could be causing the pinholing. oh also I don't stack my bisque in the kiln. Would stilting the pieces give better air flow or deform them? Thanks! Irene
I thought I would start a new subject line rather than continuing to hijack the other one. I am trying to learn how to do some basic fine tuning of my glaze firing. I am going to start by trying to correct a pinhole issue I am having with one of my more popular glazes. I think the problem is that the temperature is dropping too quickly once reached and "freezing" the glaze before it has time to smooth out and heal over. I have a Bartlett V6-CF controller on my Olympic Kiln and I glaze fire to cone 6. With help from people over on the other subject of firing schedules (thank you!) I read through the Bartlett manual again. I read it when I first got it but didn't understand most of what I was reading so bad me for not reading it again. It seemed easiest to simply cut and paste the info from the Bartlett Manual so I don't get it wrong. This is their firing schedule for cone 6: Then I found this towards the back of the manual concerning a pre programmed vary fire program called User 6. They have something called a 16-S (16 segment program) under the menu section on the controller. I played around with the controller and was able to turn on this special, 16-S, user 6 cool down program. I do have a question concerning their Important Notes section. I am using the preprogrammed slow glaze cone fire program and the preprogrammed user 6 slow cool program. I don't see anywhere to do the segment adjustment they are saying to do. What am I not getting? Once I get the programming figured out my firing schedule should look like this if I am understanding it correctly: Slow Glaze Cone 6, 2232F 150 degrees per hour to 250 degrees 400 degrees per hour to 1982 degrees 120 degrees per hour to 2232 degrees Add on the Vary-fire User 6 Program (user 6 cone 6 cool down) Temperature starts at 2232 degrees F then cools at its natural rate to 1900 degrees F Then cools at 150 degrees F until it reaches 1500 degrees F at which point it then cools at its natural rate the rest of the way down to kiln opening temperature. Am I getting this right? Will adding this onto my slow glaze schedule help reduce pinholes? T
I've been reading Clay and Glazes for the Potter by Daniel Rhodes as well as Mastering Cone 6 Glazes by Hesselberth. Reading these and watching my own firings got me to thinking... How long do thermocouples last? Mine has been fired 125 times. I think it's (I don't have my kiln log in front of me for exact numbers) 55 cone 04 slow bisque, 55 cone 6 slow glaze, 15 cone 05 fast glaze (transfers). And How do you know when your thermocouple is starting to have issues? In my last couple of firings I have had a couple of pieces develop pinholes. I'm trying to remedy this issue since I have never had it before these 2 firings. I am using the same glazes as I have been. I know it might be my bisque firing as well. To fix pinholes at what temperature should I add a hold to burn out the issue? Just a hold at the end temperature? It could also be that my thermocouple is drifting because it needs to be replaced. The cone 6 before this load did not look over fired but this cone looks a little towards the over fired range. It could just be where it was placed or something. If I run a test load through at cone 5 should I add a hold at the end temp? If so for how long? In this last load I also had a couple Amaco Blue Rutile pieces in there and they seem more brown than blue than they usually are. This can also happen if I have the glaze too thin so am not sure if Blue rutile runs brown if over fired. Thank you for helping me answer these questions.