McCoy, Jack Eugene on tue 24 nov 98
I've read that Neph Syenite can be substituted for other feldspars in a
glaze to reduce the maturing temperature by 1 to 2 cones. But when looking
composition of neph sy as compared to custer feldspar, it appears that
custer has a higer flux/alumina ratio. Would custer feldspar be an
exception to this rule?
The reason that I ask is that I saw a cone 9 recipe published along side its
cone 6 counterpart. The cone 6 recipe was identical, except that neph sy
had been substituted in equal amounts for custer feldspar. It appears that
the alumina content was increased.
Ideas anyone?
Donald G. Goldsobel on wed 25 nov 98
At 09:38 AM 11/24/98 EST, you wrote:
>----------------------------Original message----------------------------
>I've read that Neph Syenite can be substituted for other feldspars in a
>glaze to reduce the maturing temperature by 1 to 2 cones.
Custer is a potash spar and neph is a soda based mineral that some
ceramacist feel is not truly a feldspar. The primary difference is ptash
vs sodium as the primary active fluxing ingredient
Paul Lewing on thu 26 nov 98
McCoy, Jack Eugene wrote:
>
> ----------------------------Original message----------------------------
> I've read that Neph Syenite can be substituted for other feldspars in a
> glaze to reduce the maturing temperature by 1 to 2 cones. But when looking
> composition of neph sy as compared to custer feldspar, it appears that
> custer has a higer flux/alumina ratio. Would custer feldspar be an
> exception to this rule?
Hi, Jack,
First, my analyses of NS and CF indicate that they have identical
amounts of flux and alumina- 1 mole of flux and 1.04 of alumina.
Second, it is the silica amounts that are very different and are what
you need to look at. NS has 4.53 moles Si, CS has 7.10. It's that
lower amount of Si that makes NS a more powerful flux.
Third, while the predominant fluxes in both materials are K and Na,
the NS has a bit more Na, which is just a bit more powerful flux than
the K.
> The reason that I ask is that I saw a cone 9 recipe published alongside its
> cone 6 counterpart. The cone 6 recipe was identical, except that neph sy
> had been substituted in equal amounts for custer feldspar. It appears that
> the alumina content was increased.
Are you sure that the alumina was increased on a molecular level, or
was there just more clay in the recipe? If NS is substituted gram for
gram for CS, the balance of fluxes would change slightly, the alumina
would stay the same, and the silica would decrease. And the Si:Al
ratio would definitely change.
Paul Lewing, Seattle
hal mc whinnie on thu 26 nov 98
look at the molecular formula for both, the custer contains 3 more
molecules of silica for each molecula of materials then does the neph syn
this is why the substitution works
i am not sure what the alumina to silica ratio has to do with it. that
ratios is to consider surface quality.
On Tue, 24 Nov 1998 09:38:15 EST "McCoy, Jack Eugene"
writes:
>----------------------------Original
>message----------------------------
>I've read that Neph Syenite can be substituted for other feldspars in
>a
>glaze to reduce the maturing temperature by 1 to 2 cones. But when
>looking
>composition of neph sy as compared to custer feldspar, it appears that
>custer has a higer flux/alumina ratio. Would custer feldspar be an
>exception to this rule?
>
>The reason that I ask is that I saw a cone 9 recipe published along
>side its
>cone 6 counterpart. The cone 6 recipe was identical, except that neph
>sy
>had been substituted in equal amounts for custer feldspar. It appears
>that
>the alumina content was increased.
>
>Ideas anyone?
>
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Craig Martell on thu 26 nov 98
Hi:
The reason that neph sy has a lower flux to alumina ratio than custer
feldspar is neph sy is higher in alumina and lower in silica than custer so
the difference is not as great with neph sy. Custer has about 13% KNaO in
the analysis and Neph sy is about 14.4% KNaO with more Na than K.
Neph sy isn't considered a true feldspar. More like a soft soda spar but
not quite a true feldspar. At cone 6 to cone 10, neph sy fuses a lot more
than soda spars and a much more than potash spars such as custer and g-200.
If you do some fusion buttons of spars and neph sy at cone 6 and cone 10
you'll get a real visual example of how powerful a flux the soduim in neph
sy really is.
regards, Craig Martell in Oregon
Michael Banks on fri 27 nov 98
Yes Jack, Neph Sy lowers the maturation point of a glaze more than straight
potash feldspar. Yes custer has a higher flux/alumina, but neph sy is still
a more powerful flux. The reason has less to do with its chemistry than with
its mineralogical composition. Melting behavoir is not strictly a function
of chemistry, but is also dependant on mineral stability.
Nepheline Syenite is a mixture of alkali feldspar and nepheline. It is a
crushed igneous rock, minus iron/titanium minerals which are removed by
magnetic separation. Nepheline is a feldspathoid mineral which only forms
in an igneous rock when there is insufficient silica available. It is said
to be undersaturated in respect to silica. The chemical bonds in the
nepheline crystal lattice are therefore in a to a degree unsatisfyed and
potentially "silica hungry". It is for this reason that nepheline syenite
is significantly more reactive in ceramics compared to it's more stable
cousin feldspar. Nepheline aggressively attacks the lattices of other
silicates and quartz above 1100 degrees C, at least 2 cones lower than the
point when the feldspar atomic lattice starts to dissociate.
Cheers,
Michael Banks
Nelson
New Zealand
mjbanks@clear.net.nz
-------------------Original message----------------------------
I've read that Neph Syenite can be substituted for other feldspars in a
glaze to reduce the maturing temperature by 1 to 2 cones. But when looking
composition of neph sy as compared to custer feldspar, it appears that
custer has a higer flux/alumina ratio. Would custer feldspar be an
exception to this rule?
The reason that I ask is that I saw a cone 9 recipe published along side its
cone 6 counterpart. The cone 6 recipe was identical, except that neph sy
had been substituted in equal amounts for custer feldspar. It appears that
the alumina content was increased.
Tom Buck on fri 27 nov 98
Chemically, a typical feldspar is a raw material that exhibits
this molecular makeup: 1 mole flux oxides, 1 mole alumina, and 6 moles
silica (the silica varies, probably +/- 0.5 moles due to different
weathering conditions over long geological time).
Nepheline syenite is not characterized as a feldspar but as a
"syneite" and it exhibits: 1 flux oxides, 1 alumina, 4 silica.
Custer fs contains 10 wt% K2O, 3 % Na2O (13% KNaO). NSy has 9.8% Na2O,
4.6% K2O (14.4 % KNaO).
Neph Sy therefore has more alkali oxides to act as flux, and if
a recipe with 30% Custer is changed to 30% Neph Sy., the result will be
more strong flux in the recipe (11% more) with less silica and more
alumina. Yet, if the original recipe was low on alumina and high on silica
(common in C10 mixes), one ends up with a balanced mix that will melt at a
lower cone, c6/7 rather than c9/10.
Hence, some recipes are readily changed from c9/10 to c6/7 simply
by substituting Neph Sy for Custer/G200 feldspar.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
On Wed, 25 Nov 1998, Donald G. Goldsobel wrote:
> ----------------------------Original message----------------------------
> At 09:38 AM 11/24/98 EST, you wrote:
> >----------------------------Original message----------------------------
> >I've read that Neph Syenite can be substituted for other feldspars in a
> >glaze to reduce the maturing temperature by 1 to 2 cones.
>
>
> Custer is a potash spar and neph is a soda based mineral that some
> ceramacist feel is not truly a feldspar. The primary difference is ptash
> vs sodium as the primary active fluxing ingredient
>
Jim Brooks on fri 27 nov 98
i have also read that Neph Sy. does not contain any free silica... true or
not?.. any comments?
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