Janet Kaiser on sat 4 oct 03
Hi Benjamin
As bone china manufacture was confined almost exclusively to
England at one time (and may still be for all I know), I suppose
you should get an answer from us here...
Bone china developed from extremely fine stoneware and got its
name primarily because of the addition of bone ash which acts as
an additional flux to the Cornish stone or feldspar. As it is a
powerful flux it produces an extremely translucent body.
According to Ernst Rosenthal: "Bone ash possesses a certain
amount of plasticity and this property makes it possible to
compound bodies which are plastic enough to be jollied and cast
without the addition of ball clay. The only clay used in bone
china is china clay of highest quality."
He says of the bone ash additions amongst other things, "It
imparts to the body translucency even if the body is not quite
dense and not fired to vitrification point, but still porous. It
is a strong flux when small amounts are added to clay, but it is
a refractory when large amounts are added. For instance, the
lowest melting point of all bone ash + clay mixtures was found to
be that of a mixture consisting of 30% bone ash and 70% china
clay which melts at bisque fire temperature."
According to "An Encyclop=E6dia of the Ceramic Industry" (Searle,
Vol I, p. 111)
Bone China Bodies have the following composition:
China clay...............20% to 30%
Bone ash.................27% to 46%
Cornish stone.........20% to 32%
Hope this helps.
Janet Kaiser
*** IN REPLY TO THE FOLLOWING MAIL:
>Im currently enrolled in a materials analysis
>class. Ive been exploring the aspects of the ever so
>interesting clay body of Bone China. If anyone has
>any ingredients to deversify my list I would greatly
>appreciate it. In doing so this would increase the
>connection that I have with the material.
*** THE MAIL FROM benjamin jennings ENDS HERE ***
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