Craig Martell on wed 26 jul 00
Hi:
I've been reading the posts on feldspar types and have a comment or two.
I've been working on celedon glazes for a while. Looking for deep, non
watery green ones and the elusive blue celedons. I just unloaded a cone 10
R fire today with some blue celedon tests and I got some very nice real
blue celedons using only black iron oxide for color. My reason for
commenting on this is that these blue celedons are pretty flux oxide
specific. I read Ian Currie's account of the blue type in his book,
Stoneware Glazes A Systematic approach and he gives a receipe for a sky
blue celedon from Tichane. 49 potash spar, 20 whiting, 30 silica, 1 iron
oxide. The seger formula given would indicate that Tichane is using the
"ideal" potash feldspar analysis, which doesn't exist in nature, as far as
I know. .3 K2O and .7CaO in the flux column. Pretty hard to acheive
because most potash spars contain some NaO as Michael Banks has pointed out
in his post on spar types. To continue rambling on, Ian says that K is
important in the development of blue celedons and Na is not conducive to
blues. My tests bear this out. My initial trial of the Tichane receipe
used g-200 spar which has a bit more than 10% potassium. I got a blue
celedon but very blue grey. I computed the receipe into seger and the K
was a bit low at .19 moles. Then I remembered that I have a couple hundred
pounds of Kingman spar which is higher in potash at about 12%. So I
computed a seger using Kingman and got the flux column at .3 K2O, .1 NaO,
and .6 CaO, using about 55% Kingman in the receipe. Ian also says that the
silica alumina ratio for the blues should be about 12 to 1 and I was able
to get it at a bit more than 11 to 1 and this worked just fine.
My starting point with the tests I unloaded today was Kingman, whiting, and
silica. No other components in the base. Then I added 1% black iron
ox. The alumina is a bit high in this one so it's a very nice blue satin
matt celedon. I did nine more tests, adding 1% BaCo3 to each one until I
had added 10% barium to the final test. As the barium increased, the blue
intensified and the glaze also became shinier and more transparent. I'll
do some more runs of the 10% barium celedon in my next firing and send off
tests to Alfred for Ba release.
My long winded point here is that these blue celedons need the highest
potash spar one can get their hands on. If I lived in Norway, I'd be
buying up all the Norfloat I could find!!! :>) Anyway, Ian Currie was
totally right on about how to acheive these glazes. High potash content,
little or no titanium in the glaze, a silica/alumina ratio of about 12/1, a
slower maturing fire with good reduction. I'm glad I took the time to work
on these glazes because they are very soft and nice in terms of the
blue. Quite different from cobalt and or copper. My next step is to try
and make some of these blue celedons with custer and g-200 Kspars. I've
got enough Kingman to last a few years but need to look ahead I guess.
later, Craig Martell in Oregon
Jeff Lawrence on fri 28 jul 00
Hello,
As a tangent to Craig's line of commentary, why does Tichane keep talking
about using Kona feldspar for sky blue celadons? My Insight says Kona is
high soda and Tichane's discussion indicates that potash is preferred.
The blues I've gotten at cone 6 have been with custer or G-200, and the only
keepers were on iron-bearing bodies, the darker the better. The blues on a
white body were far inferior to the ones pictured in Celadon Blues.
Jeff Lawrence ph. 505-753-5913
Sun Dagger Design fx. 505-753-8074
18496 US HWY 285/84 jml@sundagger.com
Espanola, NM 87532 www.sundagger.com
Nils Lou on sat 29 jul 00
maybe Tichane is referring to Kona A-3 which I believe is a potash spar.
F-4 is soda. nils
On Fri, 28 Jul 2000, Jeff Lawrence wrote:
> Hello,
>
> As a tangent to Craig's line of commentary, why does Tichane keep talking
> about using Kona feldspar for sky blue celadons? My Insight says Kona is
> high soda and Tichane's discussion indicates that potash is preferred.
>
> The blues I've gotten at cone 6 have been with custer or G-200, and the only
> keepers were on iron-bearing bodies, the darker the better. The blues on a
> white body were far inferior to the ones pictured in Celadon Blues.
>
> Jeff Lawrence ph. 505-753-5913
> Sun Dagger Design fx. 505-753-8074
> 18496 US HWY 285/84 jml@sundagger.com
> Espanola, NM 87532 www.sundagger.com
>
> ______________________________________________________________________________
> 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.
>
Edouard Bastarache on sat 29 jul 00
Hello Nils & all,
Kona A3 is a potash spar with the following composition:
SiO2 66%
Al2O2 18.7%
Fe2O3 0.1%
Ca0 0.1%
K2O 12.0%
Na2O 2.8%
Later,
Edouard Bastarache
Dans / In "La Belle Province"
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
-----Message d'origine-----
De : Nils Lou
=C0 : CLAYART@LSV.CERAMICS.ORG
Date : 29 juillet, 2000 17:37
Objet : Re: feldspars/blue celedons
>maybe Tichane is referring to Kona A-3 which I believe is a potash spar.
>F-4 is soda. nils
>
>On Fri, 28 Jul 2000, Jeff Lawrence wrote:
>
>> Hello,
>>
>> As a tangent to Craig's line of commentary, why does Tichane keep talk=
ing
>> about using Kona feldspar for sky blue celadons? My Insight says Kona =
is
>> high soda and Tichane's discussion indicates that potash is preferred.
>>
>> The blues I've gotten at cone 6 have been with custer or G-200, and th=
e
only
>> keepers were on iron-bearing bodies, the darker the better. The blues =
on
a
>> white body were far inferior to the ones pictured in Celadon Blues.
>>
>> Jeff Lawrence ph. 505-753-5913
>> Sun Dagger Design fx. 505-753-8074
>> 18496 US HWY 285/84 jml@sundagger.com
>> Espanola, NM 87532 www.sundagger.com
>>
>>
_________________________________________________________________________=
___
__
>> 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.
>>
>
>________________________________________________________________________=
___
___
>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.
John Britt on sun 30 jul 00
Use Grolleg instead of the EPK. It is also important to use it on a
grolleg body.
John Britt
claydude@mindspring.com
Cantello Studios on sun 30 jul 00
This is more of a ? then an answer to this post. I once was told that you
used China Clay to get good celadon blue. Question How would you go about
doing this G-200 27.51 27.5% If this was your base?
Whiting 19.6 19.6%
EPK 19.97 20 % Hazard!
Flint 32.93 32.9% Hazard!
-------- ------
100 100 %
Red iron oxide 1 1 %
Bentonite 1 1 %
? Could you say Just replace the EPK with China Clay ???
Variations:
1% iron=light green 3% for dark green.
Notes:
good clear with out iron good with oxide over,
like vivika cobalt over clear on porcelain.
- ----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of Nils Lou
Sent: Saturday, July 29, 2000 12:55 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: feldspars/blue celedons
maybe Tichane is referring to Kona A-3 which I believe is a potash spar.
F-4 is soda. nils
On Fri, 28 Jul 2000, Jeff Lawrence wrote:
> Hello,
>
> As a tangent to Craig's line of commentary, why does Tichane keep talking
> about using Kona feldspar for sky blue celadons? My Insight says Kona is
> high soda and Tichane's discussion indicates that potash is preferred.
>
> The blues I've gotten at cone 6 have been with custer or G-200, and the
only
> keepers were on iron-bearing bodies, the darker the better. The blues on a
> white body were far inferior to the ones pictured in Celadon Blues.
>
> Jeff Lawrence ph. 505-753-5913
> Sun Dagger Design fx. 505-753-8074
> 18496 US HWY 285/84 jml@sundagger.com
> Espanola, NM 87532 www.sundagger.com
>
>
____________________________________________________________________________
__
> 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.
>
____________________________________________________________________________
__
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.
GURUSHAKTI@AOL.COM on mon 31 jul 00
EPK is a china clay/kaolin. What you want to avoid is clay containing
Titanium, which prevents the blue. Grolleg would be a good choice. You can
try subbing it directly for the epk. If you get some crazing because of the
shift, you can add a hair more silica.
Regards,
June
GURUSHAKTI@AOL.COM on mon 31 jul 00
Forgot to mention -- you might also want to do another test of your blue
celadon using 1 to 1 1/2 % black iron oxide instead of the red.
Regards,
June
JIMV062@AOL.COM on mon 31 jul 00
i think that EPK is China Clay.. Is that wrong?..if so... what is?
Susan Kosko on mon 31 jul 00
when i see a recipe that includes china clay, i've used english grolleg (at least
that's what my current supplier calls it).
susan kosko
new durham, nh, usa
rickmahaffey on tue 1 aug 00
Hello blue celadon seekers,
We just unloaded a kiln at school yesterday with some tests in it. One of my
students got a beautiful light blue celadon on porcelain. The spar was a soda
spar. I don't have the formula but it has few ingredients. I do know in my
experience that if you have more than about 3/4 % iron you will get greens. In
this case the glaze has 1/2% iron in it. The feldspar was Kona F4. Firing again
tomorrow with more tests. I will advise after unloading on Friday if the glaze is
still producing blues.
Rick Mahaffey
Tacoma Community College
Tacoma Washington, USA
Hank Murrow wrote:
> >Dear Craig
> >
> > Thanks for your post I have managed to solve many of the mysteries of
> >celadons but I could never get the blue. Some recipes recommend water ground
> >quarts. This suggested that the grinding was the essential but I think you
> >have it, soda looks like a culprit. I have some feldspar with a ratio of
> >potash to soda of 9 to 2 I shall be trying it forth with.
> *****Dear Paul; What is the name of this spar?
Paul Taylor on tue 1 aug 00
Dear Craig
Thanks for your post I have managed to solve many of the mysteries of
celadons but I could never get the blue. Some recipes recommend water ground
quarts. This suggested that the grinding was the essential but I think you
have it, soda looks like a culprit. I have some feldspar with a ratio of
potash to soda of 9 to 2 I shall be trying it forth with.
Cardew suggests in his book that magnesium may not help either so I shall
be leaving that out as well- to test, but I think he may have been mistaken.
My supplier also tells me that there are more pure china clays than are
generally on the market I shall be twisting his arm a little to get me the
best.
Your information may also help with my other problem allowing a little
more iron to be put into my Luan Chuan experiments with out them going dull.
I also think color may be improved by using glazes in differing layers it
is as if a differing refractory index of the two glazes melting and running
to together increase the sensation of color. This is also improved by a
modeled surface which frames smaller areas of glaze with thick runs.
One strange thing I noticed is that many of the colors have depend with
time especially within the first month. However! This is probably an
illusion The light here can be very dull some times or a emotional reaction
to my getting everything else right except the color, but I thought I might
mention it just in case it is not- or we both suffer the same.
I have also noticed that the color improves visually if the glazes are
framed by crackle or a modeled surface. The northern celadons defiantly need
a lift from a bit of relief or combing.
I hoped to have the webb site up by now so people can see what I am
talking about but I can not get the ******* thing to run on my server. I
will probably have to change the file structure and redo all the links.
Why do you use the black iron oxide and not the red synthetic which I
supposed to be less contaminated? and finer.
Of course the exiting thing about having these glazes is to put them on
the pots with our cultural influences and not just to make facsimiles of
classical chinese pots. Great times for us both
I used to worry that no one will Know the difference between my glazes and
the colored waters that have been sold as celadons for years, but I have
given up on worrying about commercial considerations with these glazes.
-- Regards Paul Taylor.
Wetport Pottery, Liscarney, County Mayo. Ireland.
Please paragraph your posts and put a blank line in between the paragraphs.
I have great difficulty reading large blocks of type from a screen.
> From: Craig Martell
> Reply-To: Ceramic Arts Discussion List
> Date: Wed, 26 Jul 2000 11:41:37 -0700
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Feldspars/blue celedons
>
> My long winded point here is that these blue celedons need the highest
> potash spar one can get their hands on. If I lived in Norway, I'd be
> buying up all the Norfloat I could find!!! :>) Anyway, Ian Currie was
> totally right on about how to acheive these glazes. High potash content,
> little or no titanium in the glaze, a silica/alumina ratio of about 12/1, a
> slower maturing fire with good reduction. I'm glad I took the time to work
> on these glazes because they are very soft and nice in terms of the
> blue. Quite different from cobalt and or copper. My next step is to try
> and make some of these blue celedons with custer and g-200 Kspars. I've
> got enough Kingman to last a few years but need to look ahead I guess.
>
> later, Craig Martell in Oregon
>
> ______________________________________________________________________________
> 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.
Hank Murrow on tue 1 aug 00
>Dear Craig
>
> Thanks for your post I have managed to solve many of the mysteries of
>celadons but I could never get the blue. Some recipes recommend water ground
>quarts. This suggested that the grinding was the essential but I think you
>have it, soda looks like a culprit. I have some feldspar with a ratio of
>potash to soda of 9 to 2 I shall be trying it forth with.
*****Dear Paul; What is the name of this spar?
>
> Cardew suggests in his book that magnesium may not help either so I shall
>be leaving that out as well- to test, but I think he may have been mistaken.
*****I use up to 10% talc in my very blue celadon based almost
exclusively on a rhyolite I collect in Canada.
>
> My supplier also tells me that there are more pure china clays than are
>generally on the market I shall be twisting his arm a little to get me the
>best.
****Look for a low-Titania one, like Grolleg. Ti kils the blue.
>
> Of course the exiting thing about having these glazes is to put them on
>the pots with our cultural influences and not just to make facsimiles of
>classical chinese pots. Great times for us both I used to worry that no
>one will Know the difference between my glazes and the colored waters that
>have been sold as celadons for years, but I have given up on worrying
>about commercial considerations with these glazes.
>-- Regards Paul Taylor.
****I think a relatively quick firing is helpful, along with a
quick cooling, to allow the micro bubbles which scatter light to remain. I
feel a small amount of Phosphorus is also helpful to get the true
Jingdezhen quality you referenced. Good Luck! Hank in Eugene
Craig Martell on wed 2 aug 00
Rick sezzz:
> One of my students got a beautiful light blue celadon on porcelain. The
> spar was a soda
>spar. I don't have the formula but it has few ingredients. I do know in my
>experience that if you have more than about 3/4 % iron you will get greens.
Hi Rick:
Well, there you go! Exceptions to everything. Could you possibly let me
know what the raw materials are in the recipe? I don't need the
percentages and that way the glaze will remain confidential if your student
wants to keep it so. I'm curious about these glazes though and would not
expect a good blue cel with a soda spar. Kona has a lot more potash than
most soda spars though and is way off the "ideal" analysis for a soda spar.
It's good that you brought up the iron issue because the % of iron will
have a strong bearing on the glaze color. My blue celedon has 1% black
iron and isn't even close to green. It's sky blue. What Currie says is
that too much iron will push a blue celedon toward the charcoal grey area
and reducing the iron will give a brighter blue. My next step with the
blue cels is to use many types of iron in varying percents to see what the
differences may be. I might also mention that additions of Alberta slip
for iron may be a good way to go because you don't have to worry about
spotting and dispersion and Alberta contains almost no titanium.
later, Craig Martell in Oregon
Paul Taylor on thu 3 aug 00
Dear Hank - I do not know the name and when I tried to find out from
Potclays I found that they are mostly on summer holiday. I have always
called it Potclays feldspar to differentiate it from the fine Finnish
feldspar they also sell which has a lower ratio of soda to potash. I expect
they import it as well. The other suppliers are probably all on holiday as
is the tradition is the north east of england. So I did not bother wasting
the calls.
I worry though about published analyses. Pottery crafts quote their
analyses of their feldspar as typical. I would have more confidence in a
word like approximate. In the same way as St Bernards and Terriers are
typical dogs but in no way approximate each other. So I will inform you of
the feldspars available to us in the north western islands of Europe after
the summer.
The china clay I use is Special porcelain from the same shower as do the
Grelog. It is a little brighter but not enough to make a difference .01 less
titanium - if you can rely on the analyses of a dug mineral a hundred
percent. My material supplier was talking of even more pure stuff that is
not in the cataloged. But maybe that's like chinese restaurants where every
body oriental looking is eating stuff you can not find on the menu, and you
wouldn't like it if you did get it, because it is full of some nasty spice,
that it would take a years stretch in a Shanghai prison to acquire a taste
for. If you are managing to get a blue using Grelog I will not be bothering
the distributor because he will have to buy a ton of any material to give me
a couple of bags. We are lucky here in Ireland to have an ex potter David
Maybry as a supplier.
I think you are right about the phosphorus since it is in most of the
analyses have either as an ingredient or a by product of the preparation of
calcium. I get away with using bone ash even though I know that the ash used
by the chinese was of vegative origin. An observation I made is that the
analyses I have for the glazes contain a higher percentage of potassium to
sodium than the minerals they used, which suggests pine ash was used because
of it,s high potassium content.
I do not know if I concur with the quick firing I shall try it. The fun is
working out which of the seemingly inconsequential actions taken to make
these glazes are important and which ones can be substituted or enhanced by
modern materials, I gave up looking for Glaze stone after I fell down a
cliff in Portercloy haven't been the same with heights since
-- Regards Paul Taylor.
Westport Pottery, Liscarney, County Mayo. Ireland.
Please paragraph your posts and put a blank line in between the paragraphs.
I have great difficulty reading large blocks of type from a screen.
> From: Hank Murrow
> Reply-To: Ceramic Arts Discussion List
> Date: Tue, 1 Aug 2000 13:26:27 -0700
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Feldspars/blue celedons
>
>> Dear Craig
>>
>> Thanks for your post I have managed to solve many of the mysteries of
>> celadons but I could never get the blue. Some recipes recommend water ground
>> quarts. This suggested that the grinding was the essential but I think you
>> have it, soda looks like a culprit. I have some feldspar with a ratio of
>> potash to soda of 9 to 2 I shall be trying it forth with.
> *****Dear Paul; What is the name of this spar?
>>
>> Cardew suggests in his book that magnesium may not help either so I shall
>> be leaving that out as well- to test, but I think he may have been mistaken.
> *****I use up to 10% talc in my very blue celadon based almost
> exclusively on a rhyolite I collect in Canada.
>>
>> My supplier also tells me that there are more pure china clays than are
>> generally on the market I shall be twisting his arm a little to get me the
>> best.
> ****Look for a low-Titania one, like Grolleg. Ti kils the blue.
>>
>> Of course the exiting thing about having these glazes is to put them on
>> the pots with our cultural influences and not just to make facsimiles of
>> classical chinese pots. Great times for us both I used to worry that no
>> one will Know the difference between my glazes and the colored waters that
>> have been sold as celadons for years, but I have given up on worrying
>> about commercial considerations with these glazes.
>
>> -- Regards Paul Taylor.
> ****I think a relatively quick firing is helpful, along with a
> quick cooling, to allow the micro bubbles which scatter light to remain. I
> feel a small amount of Phosphorus is also helpful to get the true
> Jingdezhen quality you referenced. Good Luck! Hank in Eugene
>
> ______________________________________________________________________________
> 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.
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