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What happened? Refiring earthenware pottery to repair


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Hi all,

I had a piece of pottery that developed a couple of cracks in the glaze on the handle and when my thumb rubbed it, a few chips came off.  I decided to repaint the undergalze color on where the chip was and did a thin layer of clear overglaze just where I had repainted.  Then THIS happened!!!  Can anyone tell me why?  There are places all along the handle that were perfect after the first glaze firing and after this second one (both at Cone 06), parts that I had not even touched basically burned away back to the bisque.  I am so confused.  Also, was I wrong to reapply the underglaze and overglaze and refire in an attempt to "fix" it?

Thank you in advance.  My heart is broken that this happened and I never want it to happen again!!

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That surface is rejecting the glaze. Is the blue an underglaze? That could be rejecting the glaze. Grind or sand the area that crawled and chipped. Clean it well. get rid of any grit from the sanding.  Try re-applying the underglaze and bisque first before applying the clear. Don't get it too thick.

Marcia

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I’ve had lots of similar problems...   and spent a long time trying to find out why they occurred.  Sometimes it seemed like one particular color underglaze might be problematic.   So, I learned that underglaze ages...  How long has it been since you opened the jar of  blue underglaze?  Underglaze does get old and separates, causing adhesion problems.  If that’s the case with your blue & you’ve had a while, adding some gum Arabic to the underglaze should help.  Because it only happened with the blue and not the other colors, this might be why...  Good luck!

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It's called shivering, and it's not terribly uncommon with low fire white clays. I have never heard a good explanation of why it happens with low fire whites, but maybe @glazenerd will have a good explanation. Once it happens it's tough to get glaze to stick again, but some sanding may do the trick.

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We've had this happen a lot of times at the Paint Your Own ceramics studio I used to work at. We usually would repaint the area and reglaze it and most of the time it was fine. Like Neil said, this shivering is quite common in low-fire.

I don't know why it does this but for us, it usually happened when the pieces were quite dirty to start with (people eating chips while painting their pieces :D). So maybe making sure your piece is really clean before painting and glazing could help?

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  • 1 year later...

I am very very new to ceramics, always wanted to have a go and bought myself a potters wheel when I had a "big birthday". Have managed to throw some pots and have glazed with Duncan crystal glaze which has come out rather good I thought.

I bought some Duncan Envision glazes and duly gave my pot 3 coats, left to dry well and fired yesterday at 1020 degrees as per instructions.

Clay is a low fire earthenware as I only have a small kiln that will only go to 1100 degrees.

I opened the kiln door this morning, it was totally cold, and the pot has flaky glaze just in one spot. 

Is it possible to scrape off the loose and coat up the bare place and re fire?  Do I use the same temperature? What happens to the glaze which will overlap with what is OK or should I try to wipe it away?  I think I'm a bit out of my depth!

It's a really pretty shaped pot, I was so pleased with myself and I don't want to bin it.

I would be very grateful of a bit of advise.

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