Kathie Wheater on thu 28 aug 03
>So, if you want to work with true porcelain, it will slump and there
>is nothing you can do to stop it. Your porcelain artist friends are
>correct: either plan for the slumping or make stable shapes. You
>can also make props to support wide rims during firing, but of course
>that means the bottoms of the rims cannot be glazed.'
If your rims are sagging during firing, why don't you build the rims at a higher angle to offset the sagging. Are the pieces spanning across two shelves? That can cause warping. Uneven wall thicknesses can cause warping in thrown pieces too. Thrown pieces 'unscrew' during the drying and firing process ( I'm guessing Ivor Lewis would better be
able to explain this). Porcelains can be fussy but a with little common sense and alot of experimenting you figure it out.
>OK - I have heard people say you can support a form on a bed of ? sand ? during firing
>and this would avoid slumping .... this sounded weird to me as I thought the sand would
>melt so I might have the wrong information. Also, I always use a kiln vent and all I could
>picture was fine grains of it floating onto fluid glazes on everything else.
I use silica sand to support pieces and have never had it waft about the kiln. If a kiln vent
pulled enough air to create enough turbulance for sand to blow around you would also
lose alot of heat too don't you think? That would be more of a gas firing issue. I haven't
seen it blown about in that case either. I have done parian paste porcelains, ^6 porcelains
^10 porcelains and English grolleg china clays. You simply have to deal with the clays
limitations or change claybodies.
Good Luck,
Kathie W
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