Steve Mills on sat 1 jan 11
As a matter of interest, Cornish Stone is advertised on the Potterycrafts (=
=3D
.
co.uk) website with the following description:
Cornish Stone
3.8% K2O
4% Na2O
15.3% Al2O3
72.9% SiO2
An alternative to feldspar as a high temperature flux. This partially
decomposed granite is used widely as a flux in bodies.
Steve M
On 31 December 2010 21:34, Bill Merrill wrote:
> I read on Clayart that they cannot buy Cornwall stone. Has anyone tried
> plastic Vitrox or Cornish stone as a substitute for Cornwall stone?
>
>
>
> CORNWALL STONE - (Cornish Stone) is produced in Cornwall, England. It is =
=3D
a
> Feldspathoid used frequently in clay bodies and glazes (feldspathoids are
> chemically similar to Feldspars, however, they contain only 2/3 the amoun=
=3D
t
> of Silica and, therefore, are richer in alkalies). Its unique characteris=
=3D
tic
> is the equal molecular equivalence of CaO K2O and Na2O. It can be used in=
=3D
a
> clay body when lowering the firing temperature of the body is required. I=
=3D
n a
> glaze, it will help to minimize glaze defects such as crawling or crazing
> (see Feldspar). (FROM Sheffield Pottery)
>
>
>
> Cornwall stone is another Feldspathic material used in both glazes and cl=
=3D
ay
> bodies. A typical analysis is: FROM Dan Rhodes
>
>
>
> CaO .304)
>
> NaO .340) Al203 SiO2
>
> K20 .356) 1.o75 8.10 There was some Cornwall stone I
> remember from the past that had Flourine in it. It changed it's Unity
> formula occasionally
>
> As the mine changed from si=
=3D
ts
> to site fairly often.
>
>
>
> True Cornwall stone is not available any more but Cornish stone are
> available.
>
>
>
> CORNISH stone is available and similar to Cornwall stone. It is availabl=
=3D
e
> from Seattle Pottery Supply.
>
>
>
> Many of you use porcelain or white stoneware bodies. For additional
> plasticity many of use white bentonite for plasticity, but it still has
> traces of iron. A good pasticizer that is similar to V gum is a material
> from California called HECTALITE. Hectalite has less iron than any
> bentonite plus it is more plastic. It can be expected that you would use
> less Hectalite then V gum as a plasticizer.
>
> plastic vitrox
>
> K2O/Na2O/CaO=3DD7Al2O3=3DD710SiO2-a plastic high-potash feldspathic clay,=
sim=3D
ilar
> in structure to Cornwall stone-used in place of potash feldspar in some
> porcelain bodies to increase plasticity. Toxic in inhalation (from Cerami=
=3D
cs
> Arts Daily)
>
> Seattle Pottery Supply has Cornish stone and Plastic Vitrox in stock and
> there are considerable amounts of both materials, and Hectalite on hand.
>
> Seattle Pottery Supplu Toll Free Number is 1-800-522-1975
>
>
>
>
>
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