tmartens on fri 11 dec 98
Am I right in thinking this is a high calcium feldspar?
Judging by the price here it is a high rubies and diamonds feldspar!
Is there a frit I could use instead? If there is and anyone knows
it's analysis, it would help in the twisting of Ferro's tail in this
neck of the woods.
Toni in Durbs by the Sea where holiday makers frolic in the sun and
trample the locals
Michael Banks on sat 12 dec 98
Toni,
Cornish Stone is crushed kaolinized granite and is therefore a mixture of
minerals rather than a feldspar, which is a single mineral. Four grades of
English cornish stone are marketed. The highest grades contain about 77
percent feldspar, 16 quartz , 7 kaolin and 0.5 percent fluorspar is
sometimes present.
Many potters successfully substitute mixtures of nepheline syenite, potash
feldspar, whiting and silica for the more expensive cornish stone. IMC have
published a useful newsletter (May 1989, Case Study No.7) on the subject.
Their site is at www.digitalfire.com/
Michael Banks
Nelson
New Zealand
mjbanks@clear.net.nz
-----Original Message-----
Am I right in thinking this is a high calcium feldspar?
Judging by the price here it is a high rubies and diamonds feldspar!
Is there a frit I could use instead? If there is and anyone knows
it's analysis, it would help in the twisting of Ferro's tail in this
neck of the woods.
Toni in Durbs by the Sea where holiday makers frolic in the sun and
trample the locals
David Hewitt on sat 12 dec 98
I have a Data Sheet from Cookson Ceramics Ltd., Stoke-on-Trent which
gives the following analysis for Cornish Stone:-
SiO2 73.2%
Al2O3 15.3%
Fe2O3 0.13%
TiO2 0.06%
CaO 1.47%
MgO 0.13%
Na2O 3.44%
K2O 4.45%
P2O5 0.47%
Loss @ 1025% 1.53%
This gives a Unity Formula of
K2O .358 Al2O3 1.134 SiO2 9.220
Na2O .419 Fe2O3 0.006 P2O5 0.025
CaO .198
MgO .025
I would not consider this particular analysis as 'high calcium' although
certainly higher than you would get with a potash feldspar. It is a
rather variable material as it is a crushed rock rather than a single
mineral like potash feldspar. So I am sure that you will find other
analyses quoted.
I do not know if there is a frit which matches this particular analysis,
but I am a little curious as to why you would want do find one. Is it
anything other than the price factor in the US that you mention? In the
UK this is not a problem as I can get 5kg of Cornish Stone for 5.34UK
pound and Potash Feldspar for 4.13UK pound. Not a vast difference. On
the other hand 5Kg of a fritt would likely cost something over 20UK
pounds.
David
In message , tmartens writes
>----------------------------Original message----------------------------
>Am I right in thinking this is a high calcium feldspar?
>Judging by the price here it is a high rubies and diamonds feldspar!
>Is there a frit I could use instead? If there is and anyone knows
>it's analysis, it would help in the twisting of Ferro's tail in this
>neck of the woods.
>Toni in Durbs by the Sea where holiday makers frolic in the sun and
>trample the locals
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
Fay & Ralph Loewenthal on mon 14 dec 98
David, Toni phoned me soon after sending this to
the list. I gave her James Chappell's recipe, which
I had made up and tested with local materials. I
tested it with a stoneware glaze Chessman Blue.
The glaze with the artificial recipe looked better
than the one with the genuine product. It also
cost me one twentieth that the commercially
available one costs. I should imagine that Toni,
who buys retail, would not pay more than one
tenth the price the retailers are asking. Hope this
clears the air Ralph in PE SA.
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