timbo_heff, on 04 March 2013 - 03:06 PM, said:
OffCenter, on 04 March 2013 - 11:41 AM, said:
timbo_heff, on 04 March 2013 - 10:55 AM, said:
Jeff Zamek did a nice paper on s-cracks: his conclusion is that it is all about the power wedge aka: cone up and pushing down phase.
Perhaps with these pieces you are using more clay and therefore not engaging the clay enough at that stage.
Try really making sure you are involving all the clay down low in the cone. Really push it together at the bottom. If you have a wide cone then the bottom clay is not getting involved in the power wedge.
Cone up and push down a few more times than normal and see if that solves ( in combination with the normal compressing the bottom tricks of course).
I have not had a single s crack since paying heed to this advice (knocking vigorously on wood:)
... and you can even cut this well-worked cone of clay off the wheel and flip it over and do it again. This way what will become the bottom of the pot was once part of the most-worked part of the above described cone.
I've seen people do that but won't that flip the particle orientation and defeat the alignment purpose ?
You may be right, but I don't think it changes the alignment because even though you reverse the spiral the particles are still lining up the same way. Sort of like taking a stack of plates and turning them over. The flat sides are still lined up the same. The only way you'd really mix up the alignment is if you turned the cone on its side. But, with that said, what's wrong with random particle orientation? Seems random orientation might result in less clay memory and more even shrinkage. But, most importantly, that clay that becomes the outside bottom gets well-worked. The other way, it doesn't no matter how many times you cone wedge.