Pawelpksa Posted April 1, 2018 Report Share Posted April 1, 2018 Hi, I would like to ask you for help regarding some trouble with cracking bottoms of my pieces in the kiln.effect that is not described below. When I fire in my electric kiln I can observe that the bottoms of the bodies get stack to the shelves or just crack at the bottom. See the picture here<https://1drv.ms/u/s!AkzUYiXaPPNa3TZ80pGXEUeQBfob> (often there are more severe and damaging cases) So, I think it is not: - Overheating above clay limit as I happened to different clays including porcelain. In all the cases the clays were supposed to survive the temperate of the firing (about 1230 C). - Overheating due to broken controller, because no other signs of it, it happens on every shelf. - Shelf wash because I changed it 3 times I wonder how to avoid this problem? What is the root cause? Maybe the atmosphere from the glazes or wrong heating curve (usually 80C/h to 600C, 120C/h to 1230C, 20min, skip)? Can you share your opinion? Thanks in advance Link to comment Share on other sites More sharing options...
oldlady Posted April 1, 2018 Report Share Posted April 1, 2018 picture not available. are you glazing the bottoms of the pieces that stuck? Link to comment Share on other sites More sharing options...
Pawelpksa Posted April 1, 2018 Author Report Share Posted April 1, 2018 Here is the picture. I will make better (with more severe cases) tomorrow. No, I don't glaze the bottom Link to comment Share on other sites More sharing options...
Mark C. Posted April 1, 2018 Report Share Posted April 1, 2018 Make and use your own kiln wash on shelves problem will go away. My guess Link to comment Share on other sites More sharing options...
neilestrick Posted April 1, 2018 Report Share Posted April 1, 2018 Looks like a kiln wash issue to me. Don't use the commercial stuff, especially at cone 10. Do a search here and you'll find lots of recipes for wash. Link to comment Share on other sites More sharing options...
Pawelpksa Posted April 2, 2018 Author Report Share Posted April 2, 2018 Hi, I was changing wash 3 times: twice it was commercial mixture, 3rd time my own (50-50). May you give good recipi? Other hints than wash? See more pictures on different clay. Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted April 2, 2018 Report Share Posted April 2, 2018 Is it something as simple as housekeeping? In those last 2 pictures especially, it looks like there's residue of glaze (or other things?) which is definitely going to cause your pots to stick to the shelf. Are your pots perhaps picking something up from a dirty ware board? Even if you're using wax, you still have to wipe glaze residue off with a clean sponge, using clean water. It pays to be really immaculate about feet. Link to comment Share on other sites More sharing options...
Rae Reich Posted April 2, 2018 Report Share Posted April 2, 2018 It also looks like you have very sharp edges at the transition from side to bottom. Those edges are more likely to "grab" the shelf and they might not clean up as well as a slightly smoothed over edge. I don't see traces of kiln wash left on the pots, did you grind it all off? How thickly are you applying the wash to the shelves? Link to comment Share on other sites More sharing options...
Mark C. Posted April 2, 2018 Report Share Posted April 2, 2018 Grind your shelves so there is no glaze on them-wash them with this formula mixed to heavy cream constancy . Also make the edges of pots more smooth as noted by another poster. This will cure your sticking issue 1/2 alumina hydrate 1/4 calcined EPK (bisqued to cone 08 or so) 1/4 EPK Link to comment Share on other sites More sharing options...
Rae Reich Posted April 2, 2018 Report Share Posted April 2, 2018 45 minutes ago, Mark C. said: Grind your shelves so there is no glaze on them-wash them with this formula mixed to heavy cream constancy . Also make the edges of pots more smooth as noted by another poster. This will cure your sticking issue 1/2 alumina hydrate 1/4 calcined EPK (bisqued to cone 08 or so) 1/4 EPK Adding what Mark has recommended in other posts - use a paint roller to apply the wash, clean any wash from edges of shelves. A good application should last you for several firings with just touch-ups where needed. Link to comment Share on other sites More sharing options...
Pawelpksa Posted April 2, 2018 Author Report Share Posted April 2, 2018 Hi, thanks a lot. I will grind the shelves and apply wash again with a paint roller. Regarding the idea of glazed button - the middle picture (red clay) is misleading because it was positioned on seeshells (you can see the 3 marks). But maybe you are right that they are dirty in general and same traces of old glaze could have remained on the shelves. The idea of sharp edges is very interesting. I will have to look for other post to understand what exactly you mean by smoother edges... i didn’t grind the bottoms from any wash, there was no need. Wash itself was applied in 3 runs as creamy paint. Thanks for recipe. I’m from Poland and I don’t think that ‘calcined EPK’ naming is recognized here. What exactly it is? In my recipe I use 1:1 kaolin and alumina hydrate. Regards Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted April 2, 2018 Report Share Posted April 2, 2018 EPK = kaolin Link to comment Share on other sites More sharing options...
Pawelpksa Posted April 2, 2018 Author Report Share Posted April 2, 2018 1 hour ago, Rae Reich said: calcined EPK (bisqued to cone 08 or so) Yes, sure about EPK but how to get ‘calcined EPK (bisqued to cone 08 or so)’ ? Link to comment Share on other sites More sharing options...
Tyler Miller Posted April 2, 2018 Report Share Posted April 2, 2018 Just now, Pawelpksa said: Yes, sure about EPK but how to get ‘calcined EPK (bisqued to cone 08 or so)’ ? I buy it pre-calcined from my supplier, but the studio I work at just has a bisque bowl they fill with epk and put in the bottom of their bisque loads. Link to comment Share on other sites More sharing options...
Pawelpksa Posted April 2, 2018 Author Report Share Posted April 2, 2018 Aha, thanks, seems to be simple Link to comment Share on other sites More sharing options...
Mark C. Posted April 2, 2018 Report Share Posted April 2, 2018 Yes just fire some EPK in one of your pots in a bisque fire to whatever temp you bisque to. Dump it out and brush or wash pot out and its ready for glaze fire. Mix your wash to a heavy cream consistency and roll it on with roller . I have a few posts you can search for on this topic. I put my shelves in sun to heat them up roll them in sun and let dry. two coats on new shelves. Link to comment Share on other sites More sharing options...
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