Wednesday, March 08, 2006


There is a picture, in our flickr photos, of me throwing a rather large bowl.

After the picture was taken, I let the bowl sit on the wheel for a while, to firm up a bit.

If you look closely, the bowl spreads out from the base, then transitions to the vertical.

This was a very bad thing; I didn't leave enough clay in the base to support the walls of the bowl. As I thinned out the walls, and tried to put more shape in the piece, it collapsed.

The shape and size of a thrown piece is proportional to the thickness of the piece, the 'tooth' (kinda stiffness, but not really), the centripedal acceleration due to the rotating wheel, and local gravity (I include the last for completeness, only because I've mused about the shapes I could throw in zero gee, as well as the moon and other planets. The moon would be great for shallow bowls and platters).

A larger piece needs to be thrown at a slower wheel speed than a smaller piece due to centripedal acceleration. Tooth has something to do with it as well, because if your hands aren't wet enough, you'll start peeling off hunks of clay, or stretching the piece.

I ended up cutting the bowl back twice, removing inches of diameter and pounds of clay each time, and trying again, with the same results. I finally made a platter, and have bagged the rest of the clay for recycling.

I grabbed a half bag of clay, and had some success in throwing another large bowl. I trimmed both pieces on Monday night.


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