Mari Posted October 1, 2015 Report Share Posted October 1, 2015 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! Link to comment Share on other sites More sharing options...
neilestrick Posted October 1, 2015 Report Share Posted October 1, 2015 At cone 10 it should be fine. I would not only glaze the inside, but also the lip on the outside. The rough clay isn't particularly comfortable on one's lips. It is possible for the unglazed surface to stain, but not easily. Those signs of use will give it character. Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted October 1, 2015 Report Share Posted October 1, 2015 I wouldn't worry about signs of stain on surface. If people are buying a rustic cup or using a rustic mug like that, then they are not really too worried about stains. They in fact will probably like that it has aged and gave it character like Neil said. Link to comment Share on other sites More sharing options...
bciskepottery Posted October 1, 2015 Report Share Posted October 1, 2015 You can apply a soda ash wash (1/4 cup soda ash dissolved in 1 cup hot water) to the outside; that will give the raw clay a bit of a sheen and make it feel smoother to the touch. Link to comment Share on other sites More sharing options...
Judith B Posted October 2, 2015 Report Share Posted October 2, 2015 Depending on what kind of clay you're using, you can also sand the outside of the piece once it has been fired. It will smooth it out and make it much nicer to touch, especially with the lips. Link to comment Share on other sites More sharing options...
neilestrick Posted October 2, 2015 Report Share Posted October 2, 2015 From a sales standpoint, people tend to get weirded out about unglazed clay and food. No matter how many times you tell them it's okay, they just don't want to believe it. Glazing the lip will calm them down. Link to comment Share on other sites More sharing options...
OldUberGoober Posted October 2, 2015 Report Share Posted October 2, 2015 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. Link to comment Share on other sites More sharing options...
phill Posted October 4, 2015 Report Share Posted October 4, 2015 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. Link to comment Share on other sites More sharing options...
Chris Campbell Posted October 4, 2015 Report Share Posted October 4, 2015 I agree with Judith here ... It just will not feel nice to drink from it. Make a couple and try it yourself. Glazing the lip/rim could be done artistically and enhance the cup. Link to comment Share on other sites More sharing options...
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