Monday, June 06, 2005

Thoughts on trimming porcelain bowls

A sunny,hazy afternoon.The bisc is at 900 degrees- I try to fire to 920 (sometimes I miss),finding from experience that higher means harder (to glaze)-although,of course,these are just numbers on a pyrometer display,any resemblance to reality being co-incidental and unlikely.As I write,920 comes up,and this time I'm going to soak,or maintain steady temperature,for half-an-hour or so,after talking to a potter at Raanana last week who uses the same porcelain and says that she has to fire bisc high (1000-1020) to avoid scummy rims in the glaze firing- a potential snippet of information in the continuing quest to delve into the nature of this clay,tending to support my idea that we have some organic binder or resin here,maybe not-quite- burning-out in low-fired bisc,and causing the aforementioned scumming.Or,of course,not.Glancing through the two peep-holes of the soaking kiln,I see that the top is quite a bit hotter (and the bottom cooler- by its more dull orange tint)so I guess I'll have chance to check out all possibilities.I'm not shocked at the unevenness- most of the kiln is those big pots,not many shelves,harder to estimate heat distribution.
On my pet radio station (see links) Khaled is wailing "Ouelli el Darek",and I'm trimming some almost-gone-hard porcelain bowls,fairly-aggressively-facetted-and-then- thrown-further to try to get some movement into my clay work,which tends to the stiff with porcelain.Three survived the throwing- the interface between flowing movement and collapse being delicate.The rims being quite wavy as a result,I trimmed them on a chuck,leaving the most successful til last in approved fashion- of course,that was the one that broke.So much for fashion.But it did serve to remind me how little dry strength porcelains have,gummy or not.The trimming itself was classic porcelain- a pleasure,translucent compact curls of clay with that sweetness and smoothness that only porcelain trimmings possess.I think it's time to wedge up another lump and try some teabowls:traditionally,this requires a calm mind- thank you,Mark and Jamie!
The half hour is up- I'm off to turn off the kiln.



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