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Kristy

yarn bowl dilemma

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Hey all :)

I have been attempting yarn bowls. They are easy enough to make but when they hit the glaze firing stage (fired cone 6), they wonk out on me every time. My pottery teacher and I have tried different ideas, such as thinner walls, thicker walls but they still wonk out. I am using porcelain clay as well.

My teacher suggests trying a high fire clay fired at cone 6? What are your thoughts or experiences? I'll attach a few photos. (I don't have a photo of how much the one of the left wonked out...the top cut part jutted way out and in the finished photo I posted, you can see it drooped down. Please ignore the glaze that ran. That was unfortunate as well but a seperate issue.)

Your advice is appreciated!!!

Kristy

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Edited by Kristy
typo

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Firing a cone 10 clay to cone 6 is a good avenue to explore. Yarn bowls do not need to be fully vitrified. 

I think it’s possible the horizontal design of the yarn channel is never going to work, no matter how you fire it. Asking the clay to hold its shape in such a cantilevered position is not working in partnership with the material. The yarn channeled can be redesigned so it doesn’t involve any acrobatic cantilevering.

I’ve seen other potters fire their yarn bowls on their rims. They wax the rim to keep it free of glaze. Depending on the design of the yarn channel, an upside down firing might make it easier for the clay to hold its shape. 

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I have never made these, but I would assume it has to do with the clay not having enough grog in it to support the gap. I would get a sculptural clay that has more rigidity. Something with a lot of fine grog in it maybe? I was testing out some ideas and I found that when I wedged sand and grog into my clay it was a lot more rigid in the firing.

 

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I just got an order for a yarn bowl and went to Etsy to see what they were.  In each of what I saw, the yarn channel was pretty much vertical, which is the way I'm going to go. In the case of what you are making, if you insist on the long, horizontal yarn channel, in the areas where you have clay chips, I would leave the clay intact for about 1/8", then carefully grind it out after the final firing with a Dremel tool with a carbide bit.  I think you would be better served by going to a vertical yarn channel...

JohnnyK

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@GEP raises a good point about the shape of the channel contributing to your warpage woes. But if you're committed to the horizontal channel, I wonder if filling the gap with a coil of wadding would help. I also think using a clay with a high grog/sand content would help as @Joseph Fireborn has suggested. Using a cone 10 clay but underfiring to 6 would probably yield improved results, but then you end up with the challenge of keeping your throwing slurry and trimming scraps separate from the cone 6 clay you're using for everything else. Maybe it's worth the headache, maybe not. 

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Agree that it's the almost horizontal channel that is causing the problem and also I would be looking at the amount of clay supporting the piece above the cut out. In your image, the first bowl has a heck of a lot of clay basically hanging from a narrow strip of clay at the top. One other thing I've found is the left side of the pot tends to warp outwards and throws the rim out of round which can exacerbate the sagging problem. After cutting the channel I press the top left edge of the rim in ever so slightly so that when it fires it evens out. I use smooth cone 6 clay and fire to cone 6. I had thought about using white lowfire clay but didn't want the hassle of trying to keep the low and mid fire clays separate.

yb.thumb.jpg.9939030ddbc57e602bcfa009a5b8d3c9.jpg

 

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I had the same issues.  Making a shorter, more vertical, cut helped a lot.  I also add a few percent sand and fireclay to a mix of cone 6 commercial clays to give it a little more strength at higher temps (a step in the direction of just using a cone10 clay, but with a  better chance of a consistent glaze fit).  Keeping the walls a little thicker than usual night help too. 

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Big post on this prob previously.

Think some leave the rim intact till almost dry then file it out.

Try a search on this forum.

Drying on rim .

The suggestions above can be explored also.

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Are you certain you're not over-firing ?  Could just be the nature of the glaze - but it looks like, in addition to the clay sagging, there's a lot of running in the glaze.

The smaller scroll to the left doesn't appear to have closed up very much - but the channel is almost completely filled with glaze.  The bottom of the curve to the right, where you had the wedge in the top picture, also looks like the glaze has run/sagged - like an overly thick coat of paint.

Have you had the same issue with other glazes ?  What about firing one un-glazed, using your glaze-firing schedule ?  There are plenty on the forum much more expert than I on clay/glaze interaction - but some glazes will interact with the clay body, over-fluxing it, and causing it to move a lot more than it would with different, or no glaze. 

 

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