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Bubbles In Glaze


Celia UK

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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?

 

post-13648-0-58694200-1430158766_thumb.jpgpost-13648-0-14722300-1430158785_thumb.jpg

post-13648-0-58694200-1430158766_thumb.jpg

post-13648-0-14722300-1430158785_thumb.jpg

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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......

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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.

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