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extreme crawling after bisque /glaze firing


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I started a glaze load to cone 5, but mistakenly entered the slow bisque program instead of slow glaze.  Seven hours later I noticed the temperature was much lower than it should have been,  checked the program and discovered my mistake.  I shut down the firing and restarted it the next morning, after adding a new witness cone on the top shelf.  Everything looked ok,  and this time I entered the right program.   The temperature in the kiln was about 200 degrees when this firing started.  When I opened the  cooled kiln  after the firing there were a couple pots on the top shelf that had suffered what seems to be extreme crawling.  One  seemed to have flung its  glaze off and onto a neighboring pot.   Some other pots also crawled but to a lesser extent.  The top shelf cone read cone 5 and the bottom one a bit hotter than that, tho that cone was the one from the previous firing.   Different clay bodies and glazes were involved but nothing new.    What could have happened?  You can see how the glaze pooled in the mug.  Pics below.  Thanks!

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You followed your usual process, only difference was your firing mistake?

No new glaze clay combos,, no new batches of glaze? Same glaze SG

Bisque ware all wiped down, moistened as usual?

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I wish I had noted that temperature, but I forget what it was.    If the glazes had started to melt would I have seen that when I opened it before I started the refiring?  I added a new cone,  so I had the lid up but the glazes looked then like they did when I started the firing.   At what temp do the glazes actually start to look different?  

Your suggestion makes perfect sense and I'll do that if it happens again.  Hopefully I won't need to. 

 Thanks!

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Did you mix up new batch of glazes?

I'd do a batch of test tiles prior to using your glazes again.

SG specific gravity.

Are you mixing your own glazes? 

I used to have a glaze that reacted like that and spat off pot if applied too thickly but can't remember the culprit ingredient . Gerstley???

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15 minutes ago, Babs said:

I used to have a glaze that reacted like that and spat off pot if applied too thickly but can't remember the culprit ingredient . Gerstley???

Colemanite was known for decrepitation which I agree looks alike to those glazes and them spitting like that.  I think one of the reasons people had a love/hate relationship with gerstley was the batches could really vary in their compositions and some batches contained more colemanite than others. Nw that the supplies in North America come from blended stock you don’t really hear of the decrepitation issue.

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14 hours ago, Babs said:

Did you mix up new batch of glazes?

I'd do a batch of test tiles prior to using your glazes again.

SG specific gravity.

Are you mixing your own glazes? 

I used to have a glaze that reacted like that and spat off pot if applied too thickly but can't remember the culprit ingredient . Gerstley???

My glazes are all purchased, mostly Amaco and Mayco.   Maybe gerstley is what activated the crawling in the firing mishap, and it happened to be  a perfect storm, especially for those 2 pieces.  I'm grateful the issue wasn't more widespread and that most of the load came out fine.  

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Not sure if there is quality staff at those companies, but worth trying to contact them.

I have had firings stall, power outage, you name it and fired up again as you did, without this happening, home made glazes.

Your results are crazy, but there must be a reason.

All pots from same batch of clay?

All from same bisque firing?

Are you dipping or brushing?

Dog with bone brain here

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22 minutes ago, Babs said:

Not sure if there is quality staff at those companies, but worth trying to contact them.

I have had firings stall, power outage, you name it and fired up again as you did, without this happening, home made glazes.

Your results are crazy, but there must be a reason.

All pots from same batch of clay?

All from same bisque firing?

Are you dipping or brushing?

Dog with bone brain here

Babs, I get it.  It's a mystery.   Just to clarify, I did stop the first firing and let it cool overnight to about 200 degrees before I restarted it.  There were 4 different types of clay in the kiln, including some reclaim.  Most were probably from the same bisque load, and I brush glaze, and as usual I used a wide variety of glazes.   I generally don't have any crawling in my  firings.   I can't think of anything else relevant, except maybe that the top shelf ended up a little cooler and most of the crawling was on that shelf.  Well actually I only added a new cone to the top shelf, so the bottom cone might not have been as accurate as the top, but we're only talking a few degrees here I think.   And the pots looked unfired before I started the second firing, that's what surprises me.  I hope these clues help.  I look forward to your next thoughts.

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