Bill Merrill on fri 31 dec 10
I read on Clayart that they cannot buy Cornwall stone. Has anyone tried =
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plastic Vitrox or Cornish stone as a substitute for Cornwall stone? =3D20
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CORNWALL STONE - (Cornish Stone) is produced in Cornwall, England. It is =
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a Feldspathoid used frequently in clay bodies and glazes (feldspathoids =3D
are chemically similar to Feldspars, however, they contain only 2/3 the =3D
amount of Silica and, therefore, are richer in alkalies). Its unique =3D
characteristic is the equal molecular equivalence of CaO K2O and Na2O. =3D
It can be used in a clay body when lowering the firing temperature of =3D
the body is required. In a glaze, it will help to minimize glaze defects =
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such as crawling or crazing (see Feldspar). (FROM Sheffield Pottery)
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Cornwall stone is another Feldspathic material used in both glazes and =3D
clay bodies. A typical analysis is: FROM Dan Rhodes
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CaO .304) =3D20
NaO .340) Al203 SiO2
K20 .356) 1.o75 8.10 There was some Cornwall stone I =3D
remember from the past that had Flourine in it. It changed it's Unity =3D
formula occasionally=3D20
As the mine changed from =3D
sits to site fairly often.
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True Cornwall stone is not available any more but Cornish stone are =3D
available.
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CORNISH stone is available and similar to Cornwall stone. It is =3D
available from Seattle Pottery Supply.
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Many of you use porcelain or white stoneware bodies. For additional =3D
plasticity many of use white bentonite for plasticity, but it still has =3D
traces of iron. A good pasticizer that is similar to V gum is a =3D
material from California called HECTALITE. Hectalite has less iron than =
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any bentonite plus it is more plastic. It can be expected that you =3D
would use less Hectalite then V gum as a plasticizer.
plastic vitrox=3D20
K2O/Na2O/CaO=3DD7Al2O3=3DD710SiO2-a plastic high-potash feldspathic clay, =
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similar in structure to Cornwall stone-used in place of potash feldspar =3D
in some porcelain bodies to increase plasticity. Toxic in inhalation =3D
(from Ceramics Arts Daily)
Seattle Pottery Supply has Cornish stone and Plastic Vitrox in stock =3D
and there are considerable amounts of both materials, and Hectalite on =3D
hand.
Seattle Pottery Supplu Toll Free Number is 1-800-522-1975 =3D20
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