Sunday, October 21, 2012

The Quarter Trick, Revisited

Thanks to my cyber-buddy and fellow potter, the fabulous Emily Murphy, for passing on the idea of the quarter trick, which came to her via Jordan Taylor of Stony Meadow Pottery. The original purpose of the trick was to divide the mass of clay for a large platter into two pieces instead of trying to power-center the whole lump at once,  to better judge the thickness of the center/bottom of the piece, and to improve compression with the aim of discouraging cracking.

While I have not had a problem with platters cracking (warping, yes) my cake stands are another matter. I found that I could only get a cake stand that wouldn't crack by throwing the plate and the stand in two parts and assembling at leatherhard. Since there aren't infinite, random things that cause center cracks (much as it may sometimes seem so!) the cause sort of has to be insufficient compression, differences in thickness, or water absorption. It seemed like I was compressing enough - I spent what seemed like a silly-long time at it - and I know to never leave standing water in a pot while I am throwing. I did find that it's difficult for me to judge whether the thickness of the plate within the ring is the same as the thickness of the plate without. Enter the Quarter Trick!!

I weigh out 5.5 pounds of clay to make the plate part of the cake plate, which wants to shrink to 9" to fit a standard cake diameter, so needs to start out about 10.5", with my claybody. A cake stand is best thrown upside down. I throw what is basically a pie plate, with tallish sides and without the wide rim.  Compress the living daylights out of the floor of that puppy, then place a quarter into the center.

Next, I plop a 3-lb ball of clay in the center, right on top of the quarter, center that, then open down to the quarter and pull up the ring. I can then remove the quarter and smooth the spot - taking the opportunity to compress a bit more, for luck - the wire it loose.

The piece will ned to dry to quite leatherhard before removal from the bat (tx, Captain Obvious) but will need only minimal trimming at the edge. A rubber rib works well to smooth the top surface.
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