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simatai33 posted a topic in Clay and Glaze ChemistryHello everyone! I am stumped on this issue and was wondering if anyone had any insight or advice on this. We opened our soda kiln a couple weeks ago and I had a problem with my work. I fired 64 pcs, most of which was Rods Bod clay body which also had some Red Iron Oxide slip decoration on it. I used Penn State Shino that I mixed the day that I glazed. 60% of it had major shivering! The glaze was just crumbling off and some thicker areas coming off in large pieces, leaving a grey stony finish behind. Such a bummer! See video here: https://youtu.be/0cbd0eXvYII Some things to note in this firing: - No one else's work shivered, but no one else used Rods bod or PSS Shino. - Pieces from previous firing that didn't make it in kiln and fired this time were ALL okay. They had been sitting for 6 wks and were Rods Bod with RIO decoration and PSS glaze. - I fired over two dozen spoons with Takamori clay body and PSS glaze, and NONE of them shivered. There was some crazing. - All my Rods Bod pcs with SF Shino or other glazes did not shiver. - 5 sake cups that fired cold didn't shiver. - There was crazing on several pieces. - Areas that got hit with a lot of soda on Rods Bod/PSS would shiver. - I did rush the drying process of Rods bod, drying in the sun and did a 2 hour pre-heat when I bisqued. I never had a shivering problem with Rods Bod and PSS glaze until the last two firings, which make me wonder if it's a clay body issue, a combo of clay body and glaze fit, or something happened in the glaze mixture. Or could it be the soda ash? I did find a discrepancy in our PSS recipe vs. the one from Liz Willoughby when I double checked today; we use 4.9 OM4 amount instead of her 14.9 OM4 amt, and I wonder if that makes a difference in anything. SODA ASH SPRAY RECIPE 1 lb soda ash to 1/2 gal water PENN STATE SHINO RECIPE - LIZ WILLOUGHBY 14.6 Neph Synite 7.8 Soda ash (light) 9.7 EPK 4.9 OM4 34.0 F4 feldspar 29.0 Spodumene
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?
I thought I'd throw this out there b/c my sudden shivering problem doesn't seem to fit the mold: I've been dipping a high iron stoneware in stoneware slip at bone dry and, after a 04 bisque and a dip in clear, firing to cone 5 with great success. All of a sudden, 4 out of 12 mugs came out of the kiln with a hand full of bubbles towards the base that chipped easily like shivering. I didn't change my clay, slip, or clear glaze. Any thoughts on why this would happen all of a sudden? Cheers, Allison