Monday, June 7, 2010

Cracking Up!

Went to bed last night very happy with my newly redesigned bird feeders, only to wake to this:

These are thrown in one piece.
I have been covering them loosely, but took the plastic of last night because it was pretty humid here and they seemed to be pretty even in terms of moisture/dryness.

I dry them on this plastic grid (its a panel meant to cover an in-ceiling fluorescent light fixture) to get a little air flow all around the piece.

You can see that the one next to it has cracked all around just under the rim.
A third one has not cracked at all (knock wood).

Wondering if this is primarily a drying issue, or a compression issue. If its a drying issue, I'm wondering how better to dry these, and will I have the same challenge when I glaze them or fire them (I typically single fire to cone 10).

If its an issue with my throwing, I'm wondering if there is something I should be doing such as making the "plate" part thicker, compressing differently etc.
I typically run a wire under the piece after throwing but leave it on the bat till its leather hard.

Thanks Clay Gurus, for any thoughts!


Bonnie Staffel said...

My thought is that it is a drying issue. If you apply water wax on the flange portion of the feeder, it will slow down the drying of the rim. Or else you could cover the flange with plastic wrap to keep it from drying too fast. There is no where for the clay to go but to crack because the rim is dry already before the center part. Bonnie Staffel

cactus5225 said...

You are right in that it is a drying issue and not a throwing issue. As you know the piece cracks because of shrinkage. Thicker = wetter. When the thinner part dries it becomes stationary, while the thicker part is still drying and shrinking ergo crack! Bonnie is correct in her suggestions about slower drying, I would add that making the flange a little thicker would help. Plus, don't handle the piece to much.

Sister Creek Potter said...

I would wrap the whole thing up in plastic for a while--couple days. Then wrap with light weight cloth (maybe a tee-shirt) with plastic loosley draped over. I've never tried the wax but that might help. Also, I always put my pieces on a piece or two of newspaper/newsprint as soon as I can take it off the wheel. The paper wrinkles up as the piece shrinks on drying.

Castle Rock Pottery said...

Yup, I agree it's a drying issue. The outside of the base has dried faster than the inside parts. I've had good luck with this process -- taking a dampened cloth and carefully drape it around the edge/part that is drying faster. This will soften that area. Then drape the whole thing with plastic to slow down the dry. Check it often until the outer part has softened (every hour or so ... depending on conditions). Then when it's consistently softened up, carefully re-form, re-fill in the cracked area by hand, leaving no holes, and cover/drape allowing a slow dry. You *might* be able to save them. CUDOS to you -- It's a pretty design!

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