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AndrewNorrell

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About AndrewNorrell

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  1. I just unloaded the cone 5 test. I fired slowly after cone 04 to be extra cautious, and slowed the cool with the switches at 40% for 4 hours. Tiles came out to 2.8% porosity, high but functional. There is no more bloating or crazing. There was a whole set of experimental mugs ready to go on this clay body so I threw them in. 2 plates put in crazed. So the fit isn't perfect, but the mugs are functional. So, even with all the glaring warning signs in the recipes, they probably work but aren't great. These problems are mostly due to my novice approach to a manual firing, over firing then under firing a not very stable recipe. I doubt the cone 6 firing had anywhere near even temps in the kiln, causing some of it to reach cone 7. Could the cone 5 firing have left the glaze short of fitting to the clay body making the plates craze?.... instead of asking I'll do my testing first. In the future I'll get opinions on clay/ glaze recipes before using them, fire with proper schedules, and use guide cones.
  2. Hi Nerd, I apologize for the typo when I copy pasted the recipe. I had already subbed Red Art for availability. Is it possible to bloat an unvitrified clay? From what I understand about bloating is that fast overfiring causes bloating because gasses become trapped in already formed glass, and that it takes flux to form glass at lower temps. So I thought that the ingredients might have been unstable, forming too much gas and there being too much flux causing vitrification too early. The KNaO is 2.82 molar, I'll post the rest of the fluxes molarity and a better test Wednesday. The plan is going to be to slow down at around 2000F (I have no temp readout) and fire to just below cone 6. I don't think discussing the issues is useful without a proper test.
  3. Hoping for advice on if I should continue testing, changing the firing schedules, or just choose a different glaze clay combo. Problems here are bloating and crazing. I used a clear cone 6 glaze to test on cone 6 stoneware. The 4.6 cubic foot electric kiln was mostly empty, which I think let to some of my issues. Also, this is a manual kiln with no pyrometer. My temperature estimates are based on color and cones. I used Heath A2V cone 6 Silica 35.4 Gerstley Borate 29.2 Nepheline Syenite (Theoretical) 20 EPK 6.6 Strontium Carbonate 5.7 Wollastonite (Theoretical) 2.5 Dolomite. 0.6 Cone 6 Stoneware Cushing's Handbook (#4 on p.38) VC Stoneware Cone 6 OM4 25 Goldart 25 Hawthorn 25 Lizella Red 10 Talc 5 Nepheline Syenite 10 I bisqued to cone 05 ( thinking of switching to cone 06) moving slowly from 200 to 1000 F, but once I passed 1300 I put all switches on high til the cone bent like we do at the kilns at my college. Through research though, I found out moving fast just after crystolysis can trap organics in the clay and this could be the cause of the bloating during glaze firing. Firing to cone 6, I shot the kiln right up at about 300F an hour... All the way to cone 6... Not doing that again.... I attempted to hold the cone 6 temp for 10 minutes, but like I said- no temperature readout. Results of the cone, test tile, and test mug are attached. Would it be wise to try this again with a slower schedule, or scrap the combo?
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