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Beardbangs posted a topic in Clay and Glaze ChemistryI hand-mix a transparent glaze, which I've used for the last year continuously with great success. The last two times I've glaze-fired, TONS of little bumps appeared, a few of them up to a cm wide (those ones looks a little more like an air bubble in the clay. The clay is white and the glaze is clear, but the bubbles that are appearing are white (so it looks like the glaze has fused to the clay body and pulled it out into bumps/bubbles. Please see the attached photo- this is what all my pieces came out like. I thought my glaze might have been contaminated so I mixed a whole new batch but the same thing happened. The only other thing I can think of that might be different is that it's more humid in the studio because it's the middle of summer. Please help! I'm getting so delayed on my orders because I keep having to re-make everything and I'm freaking out! Should I try re-firing the pieces and doing something differently, like holding it a bit? I fire my bisque to cone 06, and the glaze to cone 6. The kiln sometimes runs a little on the hot side, but I haven't found that to cause this particular problem before. I use PSH cone 6 white stoneware #519. My glaze recipe is: 25% epk, 25% silica, 10% wollastonite, 25% frit 3134, 15% feldspar minspar. Thanks in advance!
bfc2 posted a topic in Clay and Glaze ChemistryIs it possible that particularly virulent bacteria continued to respire in the drying slipware? if yes, would that show bubbles burst at the surface visible to me before firing, or not, I wonder? I made my own porcelain paper clay slip with porcelain powder, dispex, tissue and water. It's worked before but I left this one and it stank. following instructions from tutor I added a bit of bleach but the bleach didn't completely kill whatever it was, not totally. It was grey in colour. I poured vessels, they looked fine (but the smell and grey colour lingered until they were totally dry). Biscuit showed no signs of any problems. But stoneware temp and they've come out looking really vile, absolutely completely covered in small irregular bumps. I've broken them open and it's clear air pockets near to the surface predominantly. I can't see that this was clumped paper fibre as most of the gas holes are smooth in shape. It was a well mixed and as bubble-free as a liquid as I would usually have it. Therefore any burnt off paper could have escaped through usual channels. HOwever, if the paper gas could escape then why not this gas (if that's what it was)? Is this just a matter of something going too hot? many thanks.