Chuck Wagoner on mon 30 jul 07
Is there a reasonable sub for G-200? That is where the whole NC-4 =
thread
started when my supplier was giving me NC 4 as a sub for G-200. Now =
there is
some B.S. for you.=20
Thank you,
Chuck in Rocville, IN
Dave Finkelnburg on mon 30 jul 07
Chuck,
Custer Feldspar is the closes North American
feldspar to G-200 which I am aware of. A direct
substitution of one for the other usually works fine.
However, there is a slight difference in the analyses,
particularly ratio of flux to silica levels between
these two and if feldspar is a large % of a recipe,
say more than 30%, then one should use glaze
calculation to make the substitution on a molar basis
and adjust the silica level at the same time. This is
partly because a change in silica level influences
appearance and also glaze expansion (fit, aka
crazing).
Just for the record, NC-4 is a "soda" spar (has
sodium oxide, Na2O). That means it has about 50% more
sodium than a "potash" spar, but still, both have more
potassium than sodium on a weight % basis. Custer
and G-200 are "potash" spars with much more potassium
(K2O) than sodium. That said, if you add up the
sodium and potassium, commonly referred to as KNaO in
both soda and potash spars, they are generally 12 to
13% KNaO by weight. Kingman feldspar, long since gone
from the market, was exceptionally rich in potassium,
and if Moose Creek feldspar comes to market, it, too,
will be a high potassium feldspar.
Good potting,
Dave Finkelnburg
Date: Mon, 30 Jul 2007 16:43:57 -0400
From: Chuck Wagoner
Is there a reasonable sub for G-200?
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Ellen Currans on mon 30 jul 07
My question is "Why would you want a substitute for G-200?" Is it that
your supplier just ran out of it, or is there some problem with the
supply of it that I haven't heard about out here in Oregon? I buy
glaze and clay materials about twice a year and have not heard of any
shortage. I've been potting long enough to have gone from Kingman to
Custer to G-200 without too many adjustment problems. If it is just
your supplier, order from another supplier. If we are running out of
the stuff, we would all like to know.
Ellen Currans
-----Original Message-----
From: Chuck Wagoner
To: CLAYART@LSV.CERAMICS.ORG
Sent: Mon, 30 Jul 2007 1:43 pm
Subject: Re: NC-4/G-200/Sub for G-200?
Is there a reasonable sub for G-200? That is where the whole NC-4
thread
started when my supplier was giving me NC 4 as a sub for G-200. Now
there is
some B.S. for you.
Thank you,
Chuck in Rocville, IN
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Bill Merrill on mon 30 jul 07
Chuck,
Go to ceramic-materials.com/cermat/material/800.html and you can
compare G-200 with Custer feldspar. Both are high potash feldspars. I
use them both. Do a fusion button test of them to see the external look
when fired. Using the same glaze do a test of the same glaze using each
spar. I use a 10 gram fusion button form to do that type of test for
the raw material.
F-4 (soda) is similar to Unispar 50 (NC 4)
Bill
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Chuck
Wagoner
Sent: Monday, July 30, 2007 1:44 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: NC-4/G-200/Sub for G-200?
Is there a reasonable sub for G-200? That is where the whole NC-4
thread
started when my supplier was giving me NC 4 as a sub for G-200. Now
there is
some B.S. for you.=20
Thank you,
Chuck in Rocville, IN
________________________________________________________________________
______
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.
claystevslat on tue 31 jul 07
Chuck --
I sometimes use Custer -- it's close to a match.
I've tried in 3 different glazes, and they sub closely
enough that other differences (glaze thickness, how tightly
I pack that shelf in the kiln) can make more of a difference
than the substitution.
Custer is quoted as --
CaO 0.300
K2O 10.280
Na2O 2.910
Al2O3 17.350
SiO2 69.000
Fe2O3 0.120
Compared to G-200 --
Fe2O3 0.080
SiO2 66.300
Al2O3 18.500
Na2O 3.040
K2O 10.750
MgO 0.050
CaO 0.810
We just discovered that Lois A.'s problem glaze has
something like 47% of the substituted item in it.
It's almost certainly the issue with the lack of
consistency.
John H. recently posted and said that over 10% concentration
of the feldspar and he'd be suspicious that your glaze
formulation needed to be altered. That's twice as
limited as my standard (1/5th) but he's got years more
experience than me, and he's a trained professional.
If you are using a recipe that has only 10% G200, going
to Custer will raise the silica 3/10 of a percent, drop
the alumina a little over a tenth of a percent, etc.
If it's half of your glaze, you'll probably want to adjust
by raising the clay, dropping the silica, etc. This is the
sort of problem that glaze calc software is really good for.
-- Steve Slatin
--- In clayart@yahoogroups.com, Chuck Wagoner wrote:
>
> Is there a reasonable sub for G-200? That is where the whole NC-4
thread
> started when my supplier was giving me NC 4 as a sub for G-200.
Now there is
> some B.S. for you.
>
> Thank you,
>
> Chuck in Rocville, IN
Chuck Wagoner on tue 31 jul 07
I just do not have a supplier local that I can get it from and I have about
500 pounds of Custer. I use about 200 lbs of G-200 a year in my MC6G base
and I was just curious. I have no information that it is running out.
Chuck
Subject: Re: NC-4/G-200/Sub for G-200?
If we are running out of
the stuff, we would all like to know.
Ellen Currans
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