Alex Solla on thu 7 dec 06
Howdy Ivor-
This is one of those things that sounds great on paper... but.
In practice not only is it cost prohibitive but the final melt is also
woefully unpredictable. The upshot is that it is consistent in the bag,
and the fine grain ensures fairly even melt through the mix/clay.
By all means, experiment with frits, but also make
sure in your experimentation to overfire by at least 2 cones,
and underfire as well. I think that you'll find that in order
to get the frits to behave as advertized, you'll have a wicked narrow
firing range. In short, this would exacerbate the problem of
rapid slumping or lack of vitrification. One bad firing and you could
have pots fused or puddled whereas with clays containing soda spars
or neph sy, you'll just have some slumping...fyi.
In any event, it is certainly worth playing with. I would
hate to have to pay for a ton of this pricey mud! Would make
Southern Ice seem like a bargain!!!
cheers,
Alex Solla
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Ivor and
Olive Lewis
Sent: Thursday, December 07, 2006 9:41 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Mel's 4X25 Porcelain Body
Dear John Rodgers,
My main suggestion is that your select materials that have the minimum of
Iron oxide in their given analysis.
My second suggestion would be to avoid using Nepheline Syenite. There are
two reasons. First, though only slightly soluble, this can lead to
deflocculation problems and reduce plasticity. Second, Neph Sy. is a rock,
not a single mineral. There is good reason to believe it has the properties
of a Eutectic mixture which might account for the behaviour Alex Sola
describes. This may depend on the proportions of three minerals, Nepheline,
Soda Felspar and Leucite. If all three are present in a sample the Phase
Diagram (K2O-Na2O-Al2O3-SiO2, Fig 786, p 265. Phase Diagrams for Ceramists.
ACS) shows a melting point of 1020 Deg C.
Perhaps a better auxiliary body flux would be one of the higher melting
point Frits. Choose one with minimal Soda in its composition and do a line
blend with your felspar to get the mixture with the optimal fusion
temperature.
Best regards and good wishes for success.
Ivor Lewis.
Redhill,
South Australia.
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Ivor and Olive Lewis on sat 9 dec 06
Dear Alex Solla=20
I have no intention of making a cone six porcelain, never have had, =
doubt if I will ever make that choice.
Nevertheless, I hope John Rodgers pays heed to your warnings. I would =
not like to think that someone would sub Neph Sy on a one to one basis =
with Potash Felspar or that on a one to one basis with a Frit.
Thanks for your concern for the health of my kiln and its furniture.
Best regards,
Ivor
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