Chad Luberger on thu 29 dec 05
Just wondering if Custer Feldspar can be used as an acceptable substitution for G-200 Feldspar.
I'm primarily mixing glazes from Mastering Cone 6 Glazes and don't have nay G-200 on hand.
Thanks,
Chad
Judy Rohrbaugh on thu 29 dec 05
Chad, if you are testing a glaze for the first time, I would go ahead and make a test. There have been a few times that I haven't had the exact item when testing, and the glaze turned out ok. Seems I never have the right ball clay.
I just recently changed feldspars in my glazes. I looked at the chemical analysis, and there were some differences. I made test tiles up first, of course. The glazes came out ok.
Repeating myself, but make sure you test before putting on pots.
Judy Rohrbaugh
Fine Art Stoneware
Ohio
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William & Susan Schran User on thu 29 dec 05
On 12/29/05 11:47 AM, "Chad Luberger" wrote:
> Just wondering if Custer Feldspar can be used as an acceptable substitution
> for G-200 Feldspar.
> I'm primarily mixing glazes from Mastering Cone 6 Glazes and don't have nay
> G-200 on hand.
Short answer - probably, they're both potash feldspars. But you may find the
results a little different.
Recently, I mixed some ^10 reduction glazes with G-200 instead of Custer.
All of the glazes mixed with the G-200 ran and were more fluxed than those
mixed with Custer. Don't know if the effect might be the same at ^6
oxidation.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Steve Slatin on thu 29 dec 05
Chad --
G-200 is a close match to Custer, but it is not exact.
G-200 has a bit more potassium, calcium and alumina;
Custer has more silica. The COE of Custer is lower.
If the recipe in question has doesn't have too much
G-200, it'll probably sub one for one without any
problem. Steve Slatin
Chad Luberger wrote:
Just wondering if Custer Feldspar can be used as an acceptable substitution for G-200 Feldspar.
I'm primarily mixing glazes from Mastering Cone 6 Glazes and don't have nay G-200 on hand.
Steve Slatin --
And I've seen it all, I've seen it all
Through the yellow windows of the evening train...
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Ring in the New Year with Photo Calendars. Add photos, events, holidays, whatever.
Ron Roy on fri 30 dec 05
Hi Chad,
With a balanced shiny glaze I would not expect much of a difference - send
me the recipe and I'll calculate it out for you - this is the kind of thing
calculation software does very well.
RR
>Just wondering if Custer Feldspar can be used as an acceptable
>substitution for G-200 Feldspar.
>I'm primarily mixing glazes from Mastering Cone 6 Glazes and don't have
>nay G-200 on hand.
>
> Thanks,
> Chad
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Daniel Semler on sat 31 dec 05
Hi All, Chad,
As I understand it custer is a little more refractory than G200, ie. it has
comparatively less flux. This suggests that a sub of custer plus bits might be
constructed that could be made up and subbed for the G200 in recipes. David's
comments below made me think about this further.
> ... The mine manager in Georgia told me that G-200 was a blended
> product, 75% potash-based spar and 25% sodium-based spar, so you'll
> need proportionately more Custer to achieve similar results, or
> perhaps the same proportion of Custer plus a small percentage of
> another more active flux.
In case its of interest I have copied below the results of my fairly quick
attempt to demonstrate that it is at least possible, at an oxide level, to get
a pretty close match using common materials. I tend to use custer based
glazes,
so am unlikely to try this. If anyone does I'd love to hear the results.
G 200 SPAR............... 100.00 CUSTER
SPAR................. 83.40
========= F4
SPAR..................... 8.70
100.00 SODA
ASH.................... 1.60
ALUM
HYDRATE................ 3.20
CaO 0.08* 0.81 0.98
WHITING..................... 0.70
K2O 0.64* 10.69 7.70
SILICA...................... 2.40
Na2O 0.28* 3.01 3.30
=========
Fe2O3 0.00 0.08 0.03
100.00
Al2O3 1.02 18.44 12.27
SiO2 6.32 66.97 75.72 CaO 0.08*
0.80 0.97
MgO 0.00*
0.00 0.00
Cost: 1.26 K2O 0.54*
9.04 6.47
Calculated LOI: 0.16 Na2O 0.38*
4.16 4.53
Imposed LOI: Fe2O3 0.00
0.13 0.06
Si:Al: 6.17 Al2O3 1.02
18.50 12.24
SiB:Al: 6.17 SiO2 6.33
67.36 75.73
Thermal Expansion: 615.57
Formula Weight: 566.45 Cost: 1.33
Calculated LOI: 2.36
Imposed LOI:
Date: 12/31/05 Si:Al: 6.19
ID: 222 SiB:Al: 6.19
Location: Thermal Expansion: 599.76
Typecodes: Formula Weight: 563.53
As you can see the iron is up a little and a trace of MgO has been
introduced,
the latter from the whiting. Also note that the Na2O proportion has
risen a bit
against the K2O. Not likely a huge problem and perhaps pearl ash could be
subbed for the soda ash.
Thanx and have a good new year
D
David Beumee on sat 31 dec 05
Chad,
Good suggestions all. Custer is not an appropriate straight across substitution for G-200. The mine manager in Georgia told me that G-200 was a blended product, 75% potash-based spar and 25% sodium-based spar, so you'll need proportionately more Custer to achieve similar results, or perhaps the same proportion of Custer plus a small percentage of another more active flux. As has been suggested, testing is needed. It might be fun to see the results of a straight across substitution for starters.
David Beumee
Porcelain by David Beumee
www.davidbeumee.com
Lafayette, CO
-------------- Original message ----------------------
From: Chad Luberger
> Just wondering if Custer Feldspar can be used as an acceptable substitution for
> G-200 Feldspar.
> I'm primarily mixing glazes from Mastering Cone 6 Glazes and don't have nay
> G-200 on hand.
>
> Thanks,
> Chad
>
> ______________________________________________________________________________
> 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.
skiasonaranthropos@FSMAIL.NET on wed 4 jan 06
Hello David,
Custer and G-200 contain similar amounts of potash and soda feldspar.
Given the similar chemical and mineralogical composition substituting
between would necessitate only a minor reformulation
Regards,
Antony
David Beumee on wed 4 jan 06
Dear Antony,
If what you say is true, then fusion button tests fired side by side of G-200 and Custer would theoretically have similar melts. Such is not the case. The fusion button of G-200 shows a distinctly stronger melt than Custer and is far more translucent than the fusion button test of Custer, which fires quite opaque in color at cone 10 in reduction and stands up in non deformed shrunken cast of the inverted #3 Coors crusible.
David Beumee
Lafayette, CO
www.davidbeumee.com
-------------- Original message ----------------------
From: skiasonaranthropos@FSMAIL.NET
> Hello David,
> Custer and G-200 contain similar amounts of potash and soda feldspar.
> Given the similar chemical and mineralogical composition substituting
> between would necessitate only a minor reformulation
> 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.
skiasonaranthropos@FSMAIL.NET on thu 5 jan 06
Hello David,
Thank you for your message. With the information you quote I can not make
an accurate assessment of your findings regarding the dissimilarity in the
appearance of your fusion buttons. However as particle size also is an
influence were these similar as there a number of grades of Custer. Also
there factors in addition to the potash and soda feldspar concentration
that will influence the colour of the buttons, and these include amount of
Fe2O3 & TiO2, and the amount of bubble entrapped during preparation of the
buttons. What is known though are the analyses of the spars, and these are
shown below
Typical chemical analyses of G-200 and Custer are, respectively
SiO2 66.3 & 68.5
Al2O3 18.5 & 17.0
Fe2O3 0.08 & 0.15
CaO 0.8 & 0.3
MgO 0.01 & 0.01
Na2O 3.0 & 3.0
K2O 10.7 & 10.0
LOI 0.16 & 0.18
Typical mineralogically they are
Potash feldspar 64 & 60
Soda feldspar 26 & 25
Quartz 5 & 12
Other 5 and 3
Regards,
Antony
Jennifer Boyer on sat 7 jan 06
I did a direct custer for g200 substitution test last year for my main
glaze and although the glaze still was acceptable in terms of surface
it was not the same as the original and the color (cobalt/chrome combo)
was quite different. I couldn't use the custer test at all.
Jennifer
On Jan 4, 2006, at 4:00 PM, David Beumee wrote:
> Dear Antony,
> If what you say is true, then fusion button tests fired side by side
> of G-200 and Custer would theoretically have similar melts. Such is
> not the case. The fusion button of G-200 shows a distinctly stronger
> melt than Custer and is far more translucent than the fusion button
> test of Custer, which fires quite opaque in color at cone 10 in
> reduction and stands up in non deformed shrunken cast of the inverted
> #3 Coors crusible.
>
> David Beumee
> Lafayette, CO
> www.davidbeumee.com
>
> -------------- Original message ----------------------
> From: skiasonaranthropos@FSMAIL.NET
>> Hello David,
>> Custer and G-200 contain similar amounts of potash and soda feldspar.
>> Given the similar chemical and mineralogical composition substituting
>> between would necessitate only a minor reformulation
>> Regards,
>> Antony
>>
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
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