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70F or 158F - either should be cool enough to open.

Fitting glaze and clay body such that there's no crazing, nor shivering, shakes out to matching up coe, coefficient of expansion, according to authorities on the subject.

If it is the glazes that are pinging/crazing (not the kiln, or something else), the craze pattern may continue to develop for days, even months.

Shivering, clay shrinks more than the glaze, hence glaze pops off; I haven't "achieved" this ...yet


Crazing, glaze shrinks more than the clay, hence glaze cracks; I'm having this problem with clear glazes on white, light red, and coffee clays. Looking good on red and buff clays; the red clay has a microbubble problem, however, found a clear glaze that works - I believe it's 'cause the glaze stays liquid below the temp where bubbles are coming from the clay, if the bubbles are coming from the clay ...could be the glaze, but all the other clears I tried get bubbles...


Likely, imo, there's more to crazing/shivering that straight clay to glaze coe differences, however, it is the place to start. How much the glaze stretches, elasticity, is likely a factor; if  I'm remembering right, high boron glazes stretch better. Interaction between clay and glaze may also be a factor, iow, the clay influences the glaze - chemically. Any road, coe is where to start.

Tony Hansen's site (links above), that's a good resource (great resource!), also this site, where you can find many threads on glaze fit.

One more point! If you're interested in tuning your glazes to fit your clays, mixing your glazes from scratch is the way to go, for you know what's in it. Most commercial glazes don't come with formulas. Mixing your own is less expensive, long run.

Please post some pictures, identify the clays and glazes, and report back when you've overcome the problem.


about bubbles


Edited by Hulk
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The pinging you describe  is almost certainly caused by the glaze cracking as the clay is too big in expansion compared to the glaze’s expansion. The glaze is literally being torn apart by the bigger expansion of the clay, it’s not strong enough to withstand the force. The crazing  can be seen with a magnifier as a crackle pattern. On a darker colored glaze, sometimes you can’t see the crazing with a magnifier, but if you carefully hold a pot over a kettle generating steam, oftentimes you can see the crackling as the steam penetrates into the cracks. This problem is easily remedied; can you post your recipe for us to see so we can offer you help? If you are buying pre-mixed glaze there’s probably nothing that can be done other than to talk with your supply house and ask for suggestions. An awful lot of potters just accept crazing as being ok, totally unaware that their wares are significantly weaker than wares produced with a properly fitted glaze. Not a good situation if you are selling functional pots. Unless you like giving customers replacements when complaints come in.  And yes, you will likely hear from your customers who become alarmed because they can see the crackle pattern that their coffee stains made visible on the inside of a mug, for example.  

By the way, I tell students that I’d much rather have a crazing problem than a shivering problem, which is the opposite issue (glaze is too big for the clay body). With shivering, slivers of sharp glaze can come off and get accidentally ingested - not the kind of lawsuit I’d want to have to deal with. This does not mean that crazing is acceptable for functional ware, it just means your problems could potentially be much worse  if someone got injured from using your pot. Both crazing and shivering are easily fixed using glaze calculation.

I hope you take the time to read the links that Tom offered in his response. A lot of excellent info contained therein. Ask questions if you have them, all questions are good questions. :D

Best wishes to you!

Edited by Mosey Potter
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