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Hello all, wondering if you can help with a new problem. I’ve used the same earthenware body and brush on botz glaze for over a year no probs. I have an  old sitter kiln and bisque to 03 then glaze at 05 this has worked till now... suddenly my pieces are crazing about a week or two after firing (not immediately). It’s shuddering for some reason. I am making slightly chunkier pieces, could this be why? Any ideas why this is now happening would be great!

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Delayed crazing can be caused by a few things; underfiring, the clay taking in moisture, or from useage whereby heating and cooling can bring on crazing that would have happened anyways over time due to the glaze not fitting the clay. Are you using cones to verify the kiln is reaching the proper cone? Also, the chunkier pieces could be part of the problem. If you are  reaching cone 03 and and 05 then the kiln probably just needs more time to soak at the end of the firing to ensure the pots are mature all the way through. Thermal lag will effect pots more so in the middle of the shelves than those closer to the elements and most kilns without zone control like the old sitter kilns have cooler bottom and/or top shelves than the center part of the kiln.  What do you mean by "shuddering" and are these functional pots or decorative?

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@oldlady, since earthenware can still be porous enough to take glaze when fired hotter in the bisque than the glaze firing it's okay to do this. If it's a ^05 glaze that can't take going to ^03 then it's fine going hotter on the first firing as long as the bisque is still absorbent enough to take the glaze.

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Thank you everyone. As I’ve had the same practice for nearly two years I’m wondering if it’s possible that this particular tub of glaze may be the problem? I opened it to look at last evening and it’s more watery than I’m used to. It may be time to have a go at making my own.

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"It may be time to have a go at making my own."

Good for you! If starting over, I'd still choose to mix my own glazes, and try several clays; it's been a few years now, still working on it!

May I suggest taking your time researching glaze materials and recipes? Here's a resource you might find interesting:

https://insight-live.com/insight/share.php?z=wK2ZW14yNo

    The recipes may not suit your needs; the discussion may be helpful.

Did the problems coincide with opening a new container of glaze? I'm also curious if the problems coincide with opening a new bag of clay; we'd like to believe every bag of the same brand and type will behave identically.

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I've been working in clay for 28 years and I've never heard a good explanation of why low fire glazes just decide to shiver sometimes. I've seen it happen with people who have recycled their clay a bunch, but I don't know why it would just happen with fresh clay. I'd start with a fresh bottle of glaze. Then I'd try a new batch of clay- not just a different box, but a different batch. There are production batch numbers on the boxes. I just don't see thickness of the pieces being a big issue. I'd also put cones in the kiln to confirm it's firing correctly.

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