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Green Spots After Glaze Firing


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This particular glaze is the eggshell from Coyote. We mix a 25lb bags at a time and then sieve using 100 mesh. Not sure on the recipe for the dry mix, but I've attached a photo of the suggested water amount and specific gravity of eggshell. We only sieve after the initial mix. How frequently SHOULD a glaze be sieved?

Screen Shot 2019-02-21 at 12.11.09 PM.png

Edited by Ceramic Human
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What tools do you use to mix the glaze? Is there a possibility that you might be using a tool that was used to mix the teal or green glazes that might have a miniscule amount of residue that sloughs off when you mix the eggshell. It sounds too simple , but when you're talking about .008% defects is it really something worth worrying about...unless you're like my wife who will spend 3 hours to find a one cent error in her checkbook balance?

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5 minutes ago, JohnnyK said:

What tools do you use to mix the glaze? Is there a possibility that you might be using a tool that was used to mix the teal or green glazes that might have a miniscule amount of residue that sloughs off when you mix the eggshell. It sounds too simple , but when you're talking about .008% defects is it really something worth worrying about...unless you're like my wife who will spend 3 hours to find a one cent error in her checkbook balance?

I should have supplied more information. I didn't really give you guys a lot to go on. My bad. I'll look into the tools and possible contamination. A rate of 5/500 is 1% defect rate. I thought if it were a really simple fix then it would be worth reducing defect rates by 1%.  Heck, even if it's not a simple fix. You fix two or three problems like this, and reduce your defect rate by half or more. I figure that's worth the time.

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1 hour ago, liambesaw said:

You've been having issues with clay contamination, might be related?

Yeah, I thought about that and it's definitely possible, but I thought I'd ask you guys just to see if it was easy to rule out. There are so many factors, but I'm grateful to have this forum as a resource to help me get acquainted with the process.  Sometimes it makes my head spin. I don't want to be an out of touch manager.  The more information the better. 

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  • 9 months later...

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