Tony Hansen on thu 14 may 98
>This clay needs to have some specific properties.
>* It will have to be bisqued, but not necessarily as high as what we
>normally consider bisque temperature.
>* It needs to have a very fine texture/grain.
>* It needs to be "easily" crumbled or broken up once the casting is done
>so the core can be removed from the casting.
>* It needs to be able to withstand going from room temperature to about
>1700 - 1800 degrees F in an instant without shattering into a million
>pieces.
>My first thoughts about the clay body is to use a raku or stoneware body
>that has only been bisqued to 012 - 010, maybe even lower. I've also
>considered a clay body used for making crucibles. One friend has
>suggested something high in flint content. Does anyone have any thoughts
>about a clay body that might work? Does anyone know a reference that
>might mention what kind of clay the Chinese used to use?
To withstand sudden temperature change you don't want free silica
(i.e. from ball clay, silica) especially if it is a large grain size.
You want lots of kyanite, mullute,
pyrophyllite, low silica grog, molochite. As much as it will take and
still
be workable. The high grog will also make the body crumble (if it is
refractory). Use no feldspar. There is no magic to this, just take
a kaolin/bentonite base and add as much grog and low-expan mineral
as it will take and still have the workability you need.
--
T o n y H a n s e n thansen@digitalfire.com
Don't fight the glaze dragon alone
INSIGHT, Magic of Fire at http://digitalfire.com
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