David Beumee on tue 6 dec 05
Dear Ivor,
Yes, I had thought of neph sy for use in a casting body specifically because of the deflocculation that naturally occurs through sodium ion release. I had completely forgotten about the possibility of the use of bone china! I will Google bone china and see what I can find for a recipe. Thankyou!
David Beumee
-------------- Original message ----------------------
From: Ivor and Olive Lewis
> Dear David,
> The big problems with Nepheline Syenite is always the Sodium ions that
> are released when it comes into contact with water. They seems to act
> as a deflocculant. But in the case of a casting slip this might be a
> plus.
> As you suggest, one of the frits might be a good idea. My thoughts
> would be to look for something with a lower Boric oxide level and
> high Aluminium oxide so that melting was near to the chosen maturity
> temperature.
> Where to start with the practical exercise ? Possibly with the classic
> recipe using selections from a graded line blend of frit and regular
> flux.
> But if you do wish to go for slip manufacture why not explore the new
> Talc/Kaolin blends or even the old Bone China formulations.
> All the best,
> Ivor
>
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skiasonaranthropos@FSMAIL.NET on tue 6 dec 05
Hello David,
Just in case Google doesnt give you a recipe the classic formulation for
bone china is 25% kaolin, 25% china stone and 50% bone ash. Take care with
some recipes you may find quoted as if too little bone ash is used, Ive
seen as low as 10%, by definition it will mean its not bone china! The low
percentage of clay in the body aids fast casting
To maximise the whiteness and translucency for which bone china is famed
try a low iron and titania kaolin such as SSP, which being strong and
plastic will also help prior to firing.
Regards,
Antony
skiasonaranthropos@FSMAIL.NET on mon 12 dec 05
Hello David,
As I use another sort of pyrometric device I cannt advise on a cone.
However some help may be the maximum temperatures, which are biscuit fire
1220oC and glost fire 1080oC in oxidising atmosphere. Of course you=92ll
need to run a few test pieces at a range of kiln conditions
Bone china does have a shorter firing range than porcelain due to reaction
between
1. Ca compounds and feldspar minerals
2. Ca compounds with metakaolin
Consequently:
1. Tight firing control
2. Accurate weighing of raw materials, including checking and allowing
for moisture which for some may be up to 15%
Also to maximise plasticity and unfired strength use natural rather than
synthetic bone ash and Cornish stone rather than a feldspar
Hope that helps,
Antony
David Beumee on mon 12 dec 05
Thanks very much for the recipe Antony. What cone?
David Beumee
www.davidbeumee.com
-------------- Original message ----------------------
From: skiasonaranthropos@FSMAIL.NET
> Hello David,
>
> Just in case Google doesnt give you a recipe the classic formulation for
> bone china is 25% kaolin, 25% china stone and 50% bone ash. Take care with
> some recipes you may find quoted as if too little bone ash is used, Ive
> seen as low as 10%, by definition it will mean its not bone china! The low
> percentage of clay in the body aids fast casting
>
>
> To maximise the whiteness and translucency for which bone china is famed
> try a low iron and titania kaolin such as SSP, which being strong and
> plastic will also help prior to firing.
> Regards,
>
> Antony
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
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