Celia UK Posted April 27, 2015 Report Share Posted April 27, 2015 I dipped my 'sky' plate (white stoneware - Valentine's ES5), in a Potterycrafts, opaque, leaded, mid-fire glaze (that I see now has a recommended firing range to 1100oC) then sprayed areas using an airbrush, with a dilute mixture of copper carbonate and cobalt carbonate. Fired it to 1200oC (approx cone 5) - oops! With a 10 minute soak. This is the first time I've fired as high as this in my small electric kiln. The areas with the oxide over are almost ok, but the white areas have tiny bubbles - almost granular in appearance. Photos attached. So....I've realised the White opaque was fired 100oC above its recommended range, but is that likely to be the problem or is it something else? And why is this only on the areas that weren't sprayed over with the oxide wash? Any ideas? Link to comment Share on other sites More sharing options...
neilestrick Posted April 27, 2015 Report Share Posted April 27, 2015 Bigger photos, please! Link to comment Share on other sites More sharing options...
Marcia Selsor Posted April 27, 2015 Report Share Posted April 27, 2015 Yes. I think they are "boiling" or burnt...overfired.The oxide could have helped the glaze flux rather than boil. just my explanation. Marcia Link to comment Share on other sites More sharing options...
Celia UK Posted April 27, 2015 Author Report Share Posted April 27, 2015 Not sure how to insert bigger photos Neil - I had to reduce the resolution to upload them??? I've tried cropping it. Thanks Marcia - I'll try a lower temperature that covers both the clay and the glaze next time!!! Link to comment Share on other sites More sharing options...
Celia UK Posted April 27, 2015 Author Report Share Posted April 27, 2015 Just a thought - is there any mileage in refiring this at a lower temperature, or is it officially 'dead' ? Link to comment Share on other sites More sharing options...
Chilly Posted April 27, 2015 Report Share Posted April 27, 2015 Just a thought - is there any mileage in refiring this at a lower temperature, or is it officially 'dead' ? I'd re-fire. One of three things will happen: 1. No change 2. It improves/cures the problems 3. It cracks/breaks/changes colour completely! If you're not happy with it now, what have you got to lose? I've re-fired some things three or four times, usually at a lower temperature and been surprised at the change in both texture and colour. Don't forget to post photos...... Link to comment Share on other sites More sharing options...
Celia UK Posted April 28, 2015 Author Report Share Posted April 28, 2015 Thanks Ann - somehow the cropped photo pulled in nice and big AND clear. I work on my IPad and the photos are taken on it too, not sure if that makes a difference, There are obviously various ways of doing this. Next time, I'll try your route! I've done refires before and had success, but probably mostly to correct under firing or rapid cooling (I think). It was Marcia's possible explanation as it being 'burnt' that just made me think this might be an irreversible change. I'll put it in the next firing, as yu say, nothing to lose. Link to comment Share on other sites More sharing options...
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