Emma Louise Posted July 22, 2020 Report Share Posted July 22, 2020 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! Link to comment Share on other sites More sharing options...
Min Posted July 22, 2020 Report Share Posted July 22, 2020 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? Link to comment Share on other sites More sharing options...
Emma Louise Posted July 22, 2020 Author Report Share Posted July 22, 2020 @Min I meant shivering. Thank you! I did wonder if I was maybe under firing. I’m going to try a slightly longer fire on the glaze. Do you think it would benefit from a longer bisque too? Link to comment Share on other sites More sharing options...
Min Posted July 22, 2020 Report Share Posted July 22, 2020 You are seeing crazing and shivering on the same pieces? Which clay body and glaze(s) are you using? Have you used witness cones? Link to comment Share on other sites More sharing options...
neilestrick Posted July 22, 2020 Report Share Posted July 22, 2020 Are you using recycled clay or new from the bag? Link to comment Share on other sites More sharing options...
oldlady Posted July 22, 2020 Report Share Posted July 22, 2020 am i confused or isn't an 03 bisque hotter than the 05 glaze firing? what effect will that have? Link to comment Share on other sites More sharing options...
Min Posted July 22, 2020 Report Share Posted July 22, 2020 @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. Link to comment Share on other sites More sharing options...
Babs Posted July 22, 2020 Report Share Posted July 22, 2020 Fairly common practice Old Lady though 03 is a higher bisque. Link to comment Share on other sites More sharing options...
Emma Louise Posted July 23, 2020 Author Report Share Posted July 23, 2020 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. Link to comment Share on other sites More sharing options...
oldlady Posted July 23, 2020 Report Share Posted July 23, 2020 thanks, min and babs, i have not worked with earthenware but knew the factories bisque hotter than the glaze. never thought about individuals doing it. Link to comment Share on other sites More sharing options...
Hulk Posted July 23, 2020 Report Share Posted July 23, 2020 "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. Link to comment Share on other sites More sharing options...
Emma Louise Posted July 23, 2020 Author Report Share Posted July 23, 2020 Thanks @Hulk I’ll have a look at that with a cuppa! Just a new glaze pot... same bag of clay. Ive just re-glazed and fired the originals as the glaze was so watery so we’ll see. But I’m definitely going to be reading up now on glaze recipes. Thanks! Link to comment Share on other sites More sharing options...
neilestrick Posted July 23, 2020 Report Share Posted July 23, 2020 @Emma Louise are you using recycled clay at all, and if so, what is your recycling process? Link to comment Share on other sites More sharing options...
Emma Louise Posted July 23, 2020 Author Report Share Posted July 23, 2020 @neilestrick no, it’s fresh out the bag. Do you think the possibility of chunkier pieces could be a contributing factor? Link to comment Share on other sites More sharing options...
neilestrick Posted July 23, 2020 Report Share Posted July 23, 2020 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. Link to comment Share on other sites More sharing options...
Emma Louise Posted July 23, 2020 Author Report Share Posted July 23, 2020 Thanks @neilestrick got a new bag of clay and just ordered new glaze too. Will look at putting some cones in too. Link to comment Share on other sites More sharing options...
Sorcery Posted July 30, 2020 Report Share Posted July 30, 2020 On 7/23/2020 at 1:47 PM, Emma Louise said: look at putting some cones in too This should be number one IMO. Without this verification you'll likely be tail chasing forever! Sorce Link to comment Share on other sites More sharing options...
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