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Raw Fired Clay, Cleaning, And Food Safety


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Hey there. I have been toying around with the idea of making some cups with a smooth, but raw fired clay outside. The cups would be glazed inside. However, I'm concerned about it for a few reasons.

 

My understanding is that raw clay is food safe if it's not earthenware, and has been fully vitrified by firing at the correct temperature. The clay I would use for this is cone 10, and since the studio's firings are monitored by our professors and the studio manager on the gas kiln, I'm comfortable enough that I would trust that the clay would be fully vitrified. (We've never had a case of under-firing. Over-firing, however...) Would this mean that the clay would be food-safe?

 

Even though it's only the outside, I'm still concerned because when you drink from it, your lips will still touch it. I played with the idea of allowing a band of clear glaze so that one's lips won't touch the clay, but I'm averse to this idea.

 

Also, because the clay will be raw, would there be a risk of a liquid (such as coffee) staining the clay's surface if it, say, dripped out of the cup and remained in the sink/dishwasher for a while?

 

Thanks ahead of time!

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For what its worth, porcelain is generally less permeable than stoneware, and thus less likely to absorb, though any stains that get in will be more obvious on the white surface.  A smooth brown body might be the best compromise, depending on the aesthetic you're aiming for.  Porcelain would be most comfortable, all things being equal. 

 

I agree with Neil, though on the psychology; I like the look of raw clay, but I almost always glaze up near the lip of cups.

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I agree with Judith B. Sand that sucker till it's smooth. If the glaze ring is going to slow you way down, or aesthetically ruin the piece, then don't do it. Sanding works just fine. Look at Japan, they drink from raku stuff. They drink from unglazed pieces all the time. They are drinking hot beverages that way too, so leaching would more likely occur than a cold beverage. Just don't freak your customers out by telling them information they don't need to hear.

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