Steve Slatin on thu 12 jan 06
Annapoorna --
It was always my understanding that nepheline syenite
was mined in India. If true, there should be gobs of the
stuff around, though getting it milled the way you want
it may be an issue. (Some of the Indian N-S was
traditionally for the chemical market, so it's ultra-refined,
ultra-fine, high grade material.) If for whatever reason
you can't find N-S that will work, it is very similar to a
soda feldspar, and you can try to sub one for it.
Custer Feldspar is a potash feldspar. If you can't get it
economically, start by getting an analysis of locally
available potash feldspars and compare them with an
analysis of Custer. Take the closest one and do a few
tests, it'll probably work fairly well, although 'tweaking'
by adding or removing a bit of silica or alumina
or whatever may be necessary.
Likewise, you can probably adjust an available soda
spar to come close to the analysis for N-S with a
few small adjustments.
When I want to know a typical analysis for a material,
I always start (and usually stop) at the DigitalFire
database -- http://ceramic-materials.com/cermat/material/a.html
-- if I crosscheck their analyses I sometimes find slightly
different numbers used in other reliable sources, but the
difference is always slight. And they're extremely
comprehensive.
Now my last point is a narrow one -- this is just me
talking -- I would discourage you from concerning yourself
with the seger formula. For some purposes, it's a great
way of analyzing glazes, and there are folks who swear
by it, but while it makes understanding your silica/flux
ratio and alumina/flux ratio, especially with cone 10 glazes
easy, it doesn't work so well for understanding glazes
for cone 6 or below, because it concentrates all of the
information shown as the ratio of a given item to the
total of melters. The boron often used in ^6 glazes
isn't included as either a melter or a glass-former, but it can
serve as both.
If you use either weight or molar concentration of your
materials to do your analysis, you can always see the
relative concentration of any two materials in the glaze,
and see their total presence in the glaze as well. For my
money they are better ways to look at a glaze.
And in any event, there's no need to drive yourself
crazy working over analyses. There are several very
good, reasonably priced programs that will do your
analysis for you. I use Glaze Master, but others are
also very good. Several of them allow you to test
the program free and only pay if you like them -- there
may even be one or two good ones that are actual
freeware.
Best wishes -- Steve Slatin
annapoorna sitaram wrote:
hello
I am trying various glazes .But In india I cannot get (except by
importing) nepheline or custer feldspar.So I was wondering if I can
substitute potash and soda feldspar instead of nepheline or custer
feldspars. Since I am very new (still wet behind the ears stage) to
ceramics, I would not know the seger formulae for the two feldspars
available in india.
I also want to thank all the generous clay art members who have shared their
knowledge with beginners like me .
annapoorna
Steve Slatin --
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Heather Farrell on thu 12 jan 06
Hi Annaporna,
From what I have experienced, basically you *can* substitute potash and soda
feldspars for the neph sy or custer. It may change the characteristics of
the glaze somewhat, but then again, it may not. We've experimented quite a
bit with feldspars and the main change athe glazes we were using at Orton
Cone 10 was the slight difference in craze patterns in shiny glazes and a
slight variation in texture in the matte glazes.
Hope this helps.
//Heather
----- Original Message -----
From: "annapoorna sitaram"
To:
Sent: Thursday, January 12, 2006 7:09 PM
Subject: substitute for nepheline syenite and custer feldspar
hello
I am trying various glazes .But In india I cannot get (except by
importing) nepheline or custer feldspar.So I was wondering if I can
substitute potash and soda feldspar instead of nepheline or custer
feldspars. Since I am very new (still wet behind the ears stage) to
ceramics, I would not know the seger formulae for the two feldspars
available in india.
I also want to thank all the generous clay art members who have shared
their
knowledge with beginners like me .
annapoorna
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William & Susan Schran User on fri 13 jan 06
On 1/12/06 10:09 PM, "annapoorna sitaram" wrote:
> I am trying various glazes .But In india I cannot get (except by
> importing) nepheline or custer feldspar.So I was wondering if I can
> substitute potash and soda feldspar instead of nepheline or custer
> feldspars.
I would suggest simply doing a one-to-one substitution of any available
potash feldspar for the Custer feldspar and one-to-one substitution of any
soda feldspar for nepheline syenite as a starting point. You may find they
will work for your specific application.
After this first test, you could make further adjustments raising or
lowering the amount of feldspars and then adding/deleting flux, silica or
clay depending on glaze melt and glaze fit to your clay body.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
skiasonaranthropos@FSMAIL.NET on fri 13 jan 06
Hello annapoorna,
There are Indian deposits of potash feldspar that are reasonably close to
Custer feldspar. If you have found recipes calling for nepheline syenite
in books published internationally for craft potters this likely to refer
either Canadian or Norwegian material. Whilst there are Indian nepheline
syenites being mined these are not technical matches to these and also
they and suffer from high variability
My advice would be to get analyses of what you need then compare to
analyses if what you can get and reformulate accordingly. Though please
note that comparison and matching the chemical analysis is not the full
story: mineralogical content is the most factor, with particle size also
being an influence
Regards,
Antony
Ron Roy on fri 13 jan 06
Hi Annapoorna,
If you can get a typical analysis for the spars you can get there I can
answer the question.
I doubt if a spar would could replace Neph Sy - they are different in that
Neph Sy is short of silica and has more KNaO when compared to spars - makes
it a stronger melter.
RR
>hello
>I am trying various glazes .But In india I cannot get (except by
>importing) nepheline or custer feldspar.So I was wondering if I can
>substitute potash and soda feldspar instead of nepheline or custer
>feldspars. Since I am very new (still wet behind the ears stage) to
>ceramics, I would not know the seger formulae for the two feldspars
>available in india.
>I also want to thank all the generous clay art members who have shared their
>knowledge with beginners like me .
>annapoorna
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
annapoorna sitaram on fri 13 jan 06
hello
I am trying various glazes .But In india I cannot get (except by
importing) nepheline or custer feldspar.So I was wondering if I can
substitute potash and soda feldspar instead of nepheline or custer
feldspars. Since I am very new (still wet behind the ears stage) to
ceramics, I would not know the seger formulae for the two feldspars
available in india.
I also want to thank all the generous clay art members who have shared the=
ir
knowledge with beginners like me .
annapoorna
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