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Black stoneware look chalky when dry


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I have this black stoneware clay that has been drying and firing really light. It almost looks chalky when it’s dry. Even after it’s fired it’s still chalky and like it has a dusty white tinge to it. It is very dark when wet, and the first time I used it the Color was very dark after firing. Any insight into how or why this changed? Or how to fix it?

Edited by JillianEve
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11 hours ago, neilestrick said:

You said before that it was chalky after firing, too. Did you mean after the bisque or the glaze firing? How does it look after glaze firing? If it's fine after glaze firing I wouldn't worry about how it looks before firing.

Not sure about the glaze firing, I have not gotten that far yet. I’ll be running the kiln in a few days hopefully and then I’ll be able to see if this batch bisque fires chalky as well. 

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Gonna go out on a limb here and suggest all chalkiness will disappear when you fire the clay to maturity. The sample photo many suppliers use shows it’s significantly lighter at cone 03 than cone 5 or 7. Considering most people bisque between 04-06, it may be lighter still in a regular bisque.

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I poked around on the manufacturer’s website and on Dick Blick to find the MSDS. 

They’re pretty cagey about any kind of material content, only saying that it passes a number of safety tests for non-toxicity, so getting an indication of what could cause a chalky texture from ingredients is a non-starter. They do have lots of other good technical data available though, which is really nice to see. 

A couple of customer reviews mention a chalky feeling to the fired clay, but nothing like a hazing or scumming effect like you see with some earthenwares. Does it wipe off or change with wet sanding?

I agree that firing a test to maturity to see if it disappears is a good idea. If that doesn’t solve the problem, reaching out to the manufacturer would be a good next step. They do seem pretty responsive, and website translation is pretty good. 

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