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Hello all! I am a potter of several years but know that I still have a lifetime of learning to do. I have a very particular aesthetic I try to accomplish with my mugs-- essentially they are liner glazed interior with a thick coating of multiple glazes on the exterior. Many potters do this, amiright? I have been creating these intricate glazes myself for 3 years now, without issue. It seems like all of a sudden (last 4 months) I have had customers come to me saying that their piece has been fine during multiple uses, when all of a sudden they pour their hot liquid in, get a ping, and a horizontal crack appears on the vessel moving along in a ring. To me, this sounds like thermal shock dunting. Right now, I am feeling lost among the vast amount of variables and don't know where to begin trying to solve the problem. I will list all of the variables/info I have collected, and hope someone out there can tell me where to focus my attention. I appreciate this community, immensely-- Thank you in advance!! -I fire with Laguna Bmix 5 and Standard 225. Both mature at cone 6. I fire to cone 6. Majority of issues have been with the 225, with one or two bmix pieces. I worry it is a clay body issue. -My firing cycle is quite standard and the same each time. I fire at a medium rate with no slow cool (I can provide the schedule if needed). -I throw my mugs thin. -My liner glaze is always the same. Black Licorice, Cone 6 (Mastering Cone 6 glazes). Recipe below. I do add Epsom Salt to this to prevent settling. -The exterior glaze always has a bit of the glossy liner glaze above and a matte as the undercoat. Then-- there are SO MANY different glazes I use from there in my laying techniques-- application and amounts differ from piece to piece. -Each time the issue has happened with a mug, the glaze has been thick and the issue arose when the customer added freshly boiled water. My glaze is alwayyyys thick on the exterior though... What does everyone recommend? If I had my biggest wish come true, there would be an adjustment to the Liner Glaze (better COE) that would allow a more balanced thickness of glaze overall in the piece. Can you see an adjustment I can make in the recipe below? Is there a better black recipe for this? Or, Should I throw thicker to ease the tension of exterior vs interior glazing? Orrrr... Am I missing something entirely, hah! Black Licorice Material Amount Ferro Frit 3134 26 Silica 26 Custer Feldspar 22 EP Kaolin 17 Talc 5 Whiting 4 Total base recipe 100 Red Iron Oxide 9 Cobalt Oxide 2

While looking into shrinkage rates and cracks and plasticity I found a picture I immediately recognised. This picture exactly matches something I've encountered. I thought maybe it was the result of some 60 mesh silica sand I was trying but now I suspect not. As someone looking for any clue along the way this small tidbit helps a bit. Thanks Tony and anyone else at Digitalfire.

I bisque cone 6 porcelain to cone 04. Then reheated to 1150F. What I pull the pieces to lay on the horse hair I get about a 30% loss/. Cracking rate. i put the vessel on sand in the sun or on hardiboard. How do I improve my success with this type of firing.

We are jiggering plates (see attached) with an Axner Power Arm onto pure and simple hump molds. We are experiencing a tremendous amount of cracking and need help! We have done a very similar form without the jigger arm, by slabbing and attaching the foot and had no cracks at all. We used a different clay body with grog but should have worked the same as 181 (has grog). None of our other forms are experiencing cracking in the dry room, regardless of the clay body however none of the other forms are jiggered which leads us to believe it is related to jiggering. First guess is perhaps the pressure of the jigger arm is causing the clay to stick to the plaster. When the clay dries too quickly it has no where to shrink and cracks internally on the plaster, then externally on the ware boards. We don't know any way to remedy this other than just not jiggering.... Troubleshooting thus far: - Drying too quickly: Initially we thought it was only due to the forms drying too quickly and the humidity. So we brought in a humidifier into the dry room. Cracks still happening. - Clay Body (grog vs no grog): We were previously using Standard 365 (no grog). We switched to Standard 181 and...still the same amount of cracking. These are all just guesses as we are still experienced cracks galore...we'd certainly appreciate any thoughts!! Best, Ernie ernieniblack@gmail.com

Please help!! I have been using all commercial bisque and commercial underglazes (duncan and mayco) with duncan pure brilliance dipping glaze for several months now with mostly good success. This latest piece is troubling and I am not experienced enough to know what the problem is or how to fix it. Please see the attached photos. The black lettering is not "attached" to the body of the piece in a few areas and there seems to be tiny clear bubbles laying on the surface of only the black lettering. Also, the colored glaze is cracked in places, but only near the lettering... A few other side notes that may be helpful to know. #1--I attached a picture of the pyrometric cones used during this firing. The curved tip indicates that the kiln fired hotter than cone 06, correct? Is this what caused the problem? If so, how do I correct it? #2--The Pure Brilliance Dipping glaze is supposed to have a viscosity of 19-24. I was getting a 16-17. I'm pretty sure I accidentally introduced water to the glaze when wiping down the sides of the container with a sponge. I will try to siphon some of the water out, but could this lower viscosity level be the problem. #3--I had several other pieces firing at the same time and all of them turned out okay. Could the problem have been the thickness of the black underglaze applied? I am truly hoping one of you can help me, but I am also interested in other resources for troubleshooting, so I don't have to bother people. I would welcome recommendations of all kinds--books, websites, etc...

Hello, I am new to this forum and new to mixing and firing my own cone 6 glazes in an electric kiln. Boy, what a learning curve! I have much to learn. I'm grateful to you guys for posting so much useful information here:) I just fired a small kiln load of pcs of different stoneware clay bodies with Turner White recipe that I found on Ceramic Arts Daily. I thought it would be a stable fool-proof glaze so I regrettably did not test. My kiln has been overfiring, so this firing I made the adjustment of firing to cone 5, holding for 15 minutes. My pyrometer cone reached cone 6, so temperature is good...but....maybe some improvements still need to be made. The turner white came out different on different clay bodies. On Venus White clay (which has some grog) and B-mix clay, it came out an undesirable chalky, super matt. The surface almost feels like clay body. There was also some crawling happening on the Venus White clay body pcs. On red b-mix and electric brown, the finish was a tiny bit more satin matt...but not much more. I also noticed a lot of crackling, popping well after the pieces had cooled down. On some of the Venus White pcs, lots of crazing where I had dripped Leach Blue over the Turner White. What do you think the problem could be? Could some of this have to do with kiln temperature and/or cool down? And could I save these pieces by coating with clear glaze and re-firing? Or mix a new batch of turner white glaze with additional chemical to increase sheen?