Sam Kelly on wed 22 mar 06
Hi to all. I live in Australia so I don't know how different the
properties of the glaze make up is between you and me, but this works in
my 10 cu.ft. kiln. Cone 9, gas reduction starts at 950degC
3kg mix to 3 litres water
Potash feldspar 1200
Whiting 120
Silica 960
Bone Ash(synthetic) 90
Kaolin (ekalite 2) 180
Red Iron Oxide 30
Heavy reduction, if you use an oxygen probe its 0.66 all the way through
with a 1 hour soak at cone 9 which is the last hour of a 10 hour firing.
http://home.exetel.com.au/pottery/images/Coffee Mug/blue celadon.jpg
good luck, Sam
Crista Nelson on wed 22 mar 06
Have you ever fired this in reduction to a cone 10, if so did it turn out as
nice or was the color not as good as it is at a cone 9?? just wondering
because we fire to a cone 10.. thanks, crista...
Craig Martell on thu 23 mar 06
Sam was saying, with regard to his blue celadon glaze:
>Hi to all. I live in Australia so I don't know how different the
>properties of the glaze make up is between you and me
Hello Sam:
The chemical structure of this glaze corresponds to what I've used to make
blue celadons here in the US.
I don't know what feldspar you are using but I guessed that it might be
Australian Potash Feldspar. I have analyses for this spar and also Ekalite
Kaolin in my glaze calc program so I ran the glaze and found that all the
critical elements for a solution iron blue were there in the correct
parameters for the blue. The molecular formula that I've used has 0.3 K20
and yours has about 0.35. This is a good amount to produce the iron
blue. Ca0 is usually around 0.5 and yours is 0.488. Essentially, right on!
The biggest difference is the silica/alumina ratio. My blues have a Si/Al
ratio of about 12/1, with the Al203 at about 0.5 and the silica at about
5.5 molecular equivalents. Your glaze has an Si/Al ratio of 9.75/1 and the
alumina is at 0.737 and the silica is at 7.182 both are very high in
relation to the limits we use here in the US.
I don't use bone ash in the blue celadons but I do add a small amount of
barium carbonate. Usually about 4%. This enhances the blue.
I wonder about your glaze possibly being a solution blue celadon and an
optical blue chun at the same time. There are ideals for each blue effect
present in your glaze. The P2O5, from the bone ash and the high level of
silica could very well produce the chun blue effect too.
I tried to take a peek at your glaze but I was denied access. Perhaps I'll
recalculate the recipe for american raw materials and give it a try. I'll
fire in a couple of days and I'll report results to the list if anyone is
interested.
regards, Craig Martell Hopewell, Oregon
Sam Kelly on thu 23 mar 06
Don't know, I dought there is much difference between soaking for an hour
at cone 9 and shutting down at cone 10?. Give it go.
Sam
Veena Raghavan on fri 24 mar 06
Hi Craig,
Yes, please and thank you.
In a message dated 3/24/2006 7:58:12 AM Eastern Standard Time,
ashglaze@WVI.COM writes:
>
> I tried to take a peek at your glaze but I was denied access. Perhaps I'll
> recalculate the recipe for american raw materials and give it a try. I'll
> fire in a couple of days and I'll report results to the list if anyone is
> interested.
VeenaRaghavan@cs.com
Des & Jan Howard on sat 25 mar 06
Craig
I got a look at the blue glaze on Sam's site. My word! A nice one.
Somewhere I found a mol formula for what is purported to be your blue
celadon.
Blue Celadon cone 10 Reduction
BaO 0.10
CaO 0.46
K2O 0.30
Na2O 0.13
Al2O3 0.48
SiO2 5.77
silica/alumina ratio 11.97/1
Converted to my materials
potash feldspar 49.6
silica 36.14
mudgee limestone 9.16
clay ceram 1.14
barium carbonate 3.95
There may be ideal materials, but, I prefer to use local wherever possible.
Resulting mol formula
Na2O 0.14 Al2O3 0.48 SiO2 5.78
K2O 0.30 TiO2 0.00
MgO 0.00 Fe2O3 0.04
CaO 0.46
BaO 0.10
Alumina:Silica ratio is 1.00:12.02
Test fired Cone 10 R
A tad overfired at C10, clear blue, slight tinge of (to me) indigo.
Sam's recipe Cone 9 R
potash feldspar 47.06
silica 37.65
whiting 4.71
kaolin (ekalite 2) 7.06
bone ash (synthetic) 3.53
Converted to mol formula
Na2O 0.16 Al2O3 0.66 SiO2 7.19
K2O 0.34 P2O5 0.06
MgO 0.01 TiO2 0.01
CaO 0.49 Fe2O3 0.05
Alumina:Silica ratio is 1.00:10.93
Then back to recipe using local mats again.
potash feldspar 46.99
silica 37.66
mudgee limestone 4.73
clay ceram 7.1
bone ash (natural) 3.52
+ red iron oxide 1.17
Resulting mol formula
Na2O 0.16 Al2O3 0.66 SiO2 7.20
K2O 0.34 P2O5 0.06
MgO 0.01 TiO2 0.01
CaO 0.49 Fe2O3 0.05
Alumina:Silica ratio is 1.00:10.93
Test fired Cone 10 R
Definitely underfired, back to drawing board.
Hmm...one overfired, one underfired...try blending??
My rule of thumb, generalisation, whatever
Optical blue effect - recipe contains bone ash &/or magnesia, no added
iron - Jun glaze .
Solution blue effect - recipe contains added iron, barium - Iron blue
celadon.
Including boron is adding another dimension.
Must get some rice hulls burned to continue the tests.
Lotsa fun for all the family.
Read
Ian Currie's "Stoneware Glazes" section on Chuns.
Cardew's article "Chun Glazes" in "Pottery in Australia" 7/1
Tichane's "Celadon Blues"
AND
Check Clayart archives
Des
Craig Martell wrote:
> The chemical structure of this glaze corresponds to what I've used to
> make
> blue celadons here in the US.
>
> I don't know what feldspar you are using but I guessed that it might be
> Australian Potash Feldspar. I have analyses for this spar and also
> Ekalite
> Kaolin in my glaze calc program so I ran the glaze and found that all the
> critical elements for a solution iron blue were there in the correct
> parameters for the blue. The molecular formula that I've used has 0.3
> K20
> and yours has about 0.35. This is a good amount to produce the iron
> blue. Ca0 is usually around 0.5 and yours is 0.488. Essentially,
> right on!
>
> The biggest difference is the silica/alumina ratio. My blues have a
> Si/Al
> ratio of about 12/1, with the Al203 at about 0.5 and the silica at about
> 5.5 molecular equivalents. Your glaze has an Si/Al ratio of 9.75/1
> and the
> alumina is at 0.737 and the silica is at 7.182 both are very high in
> relation to the limits we use here in the US.
>
> I don't use bone ash in the blue celadons but I do add a small amount of
> barium carbonate. Usually about 4%. This enhances the blue.
>
> I wonder about your glaze possibly being a solution blue celadon and an
> optical blue chun at the same time. There are ideals for each blue
> effect
> present in your glaze. The P2O5, from the bone ash and the high level of
> silica could very well produce the chun blue effect too.
>
> I tried to take a peek at your glaze but I was denied access. Perhaps
> I'll
> recalculate the recipe for american raw materials and give it a try.
> I'll
> fire in a couple of days and I'll report results to the list if anyone is
> interested.
Interested!
You betcha sweet little blue celadon we are!!
D
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Sam Kelly on sun 26 mar 06
Hi to all, yes the site was down for maintenance, working now.
Not sure what is meant by the below statement(optical), one thing is
though I know absolutley nothing about converting glaze to formula, what I
do is put at least 25 test tiles in each firing and play and modify from
there, running line blends up, down ,left and right, basically its my
hobbie of hobbies and most of the time I will look at the test tiles
before I bother with the pots that have been ordered and sold.
My glaze to look at on a pot looks solid(for another word), but if you put
anything on the pot before you apply the glaze it shows straight through
the glaze after firing. I have also made this glaze substituting the red
iron oxide with crocus martis in the same amount producing a slightly
different blue. I have given this glaze(liquid) to 2 different friends to
fire in thier own kilns, one came out more grey then blue, the other a
beautiful green celadon. So what do you make from that, we all know what
that means, you fire your kiln to what you are comfortable with and what
gives the results your customer wants, doesn't mean what I have given here
will work for some, if any. By the way the potash feldspar is known here
as FPR200.
A potter I did a workshop with(Paul Davis) had a blue celadon which was
like looking through glass, he gave me the make up of the glaze but dammed
if I can get it to work(yet). To colour his glaze he calcines silica and
red iron oxide at 6 to 1. Now if you do this to 1000degC(bisque) it is a
nice light red colour. Do it at cone 9(10 half down) reduction and its
black.
Bone ash does some great things in glazes, also another tip, substitute
your gerstly borate for (Aust)frit4108. I have run a heap of tests and i
don't know whats being sold nowadays as Gerstly Borate but its not all the
same.
This is a blue chun, on its own very ordinary. On top of a tenmoku with a
tested water content and application thickness its orgasmic.
http://home.exetel.com.au/pottery/images/Coffee Mug/tenmoku blue chun.jpg
Sam
===========================================================
RE:
I wonder about your glaze possibly being a solution blue celadon and an
optical blue chun at the same time. There are ideals for each blue effect
present in your glaze. The P2O5, from the bone ash and the high level of
silica could very well produce the chun blue effect too.
Craig Martell on sun 26 mar 06
Des commented:
>I got a look at the blue glaze on Sam's site. My word! A nice one.
Hello Des:
With help from Maurice Weitman I was able to pull up the thumbnails of
Sam's glaze and take a look. Yes, it is a nice blue celadon.
>Somewhere I found a mol formula for what is purported to be your blue celadon.
Yes, I think I posted this to Clayart not long ago for someone in the UK
asking about blue celadons.
>Test fired Cone 10 R. A tad overfired at C10, clear blue, slight tinge of
>(to me) indigo.
Don't know what to say about the overfired result. I fire to 1280 C with
an hour soak in neutral at cone 10 and the glaze seems just right to
me. Probably some difference in the materials even though your seger
formula says you are using essentially the same glaze.
>Sam's recipe Cone 9 R
>Definitely underfired, back to drawing board.
Rats! But, when I looked at the mol formula for Sam's glaze it looked like
a possible cone 11 or so blue celadon. I think you could just lower the
alumina and silica while maintaining the same Si/Al ratio and it would be
fine. Kind of puzzling though because it seems to work just fine for Sam
at cone 9R. Sam may be doing a longer fire with more heat work involved.
regards, Craig Martell Hopewell, Oregon
Craig Martell on sun 26 mar 06
Sam says:
>Not sure what is meant by the below statement(optical),
Hello Sam:
I was commenting that with the high silica and the bone ash in your glaze
there is the possibility of producing a chun blue effect which is
accomplished through "light scattering" and this is an optical blue. True
blue celadons are blue because the iron is taken into solution and the blue
is coming from the glazes chemical influence on the iron. I've found
through testing that one needs to have a high level of potassium in the
glaze and as little titanium as possible to make the iron blue. I'm sure,
after seeing your glaze that it's a blue celadon. I was only speculating
that there may be a possibility of the chun blue too. Not the case here.
>one thing is though I know absolutley nothing about converting glaze to
>formula
With the references to molecular formula I was just trying to point out
some similarities with blues I've done and the blue that you've made in
Australia. Even though you didn't calculate any of this your glaze is very
good and has a good level of potassium for the iron blue. Good work!
> I have given this glaze(liquid) to 2 different friends to fire in thier
> own kilns, one came out more grey then blue, the other a
>beautiful green celadon. So what do you make from that
I've seen blue celadons go grey when they are applied to thin. It could
also be the clay that is being used. The sky blue celadons do best on
porcelain clays with very low iron and especially low titanium. The green
celadon color could very well be from a body that's higher in
titanium. This will sometimes turn a blue cel green.
regards, Craig Martell Hopewell, Oregon
Des & Jan Howard on mon 27 mar 06
Craig
I'm probably being overly picky. It is a nice glaze, I happen to like
celadons that aren't too glassy.
I'll try the test again, this time using 'purer' materials (ptooie!)
just for stamps.
Trying Sam's recipe again at a higher cone is definitely a thought.
Didn't have a lot of room over for extra test tile strips last kiln, had a
stack of grey & white stoneware clay test strips with high calcium matts
& satins in this time, revisiting some work I did early 70's.
Craig Martell wrote:
> Des commented:
>
>> Test fired Cone 10 R. A tad overfired at C10, clear blue, slight
>> tinge of
>> (to me) indigo.
>
>
> Don't know what to say about the overfired result. I fire to 1280 C with
> an hour soak in neutral at cone 10 and the glaze seems just right to
> me. Probably some difference in the materials even though your seger
> formula says you are using essentially the same glaze.
>
>> Sam's recipe Cone 9 R
>> Definitely underfired, back to drawing board.
>
>
> Rats! But, when I looked at the mol formula for Sam's glaze it looked
> like
> a possible cone 11 or so blue celadon. I think you could just lower the
> alumina and silica while maintaining the same Si/Al ratio and it would be
> fine. Kind of puzzling though because it seems to work just fine for Sam
> at cone 9R. Sam may be doing a longer fire with more heat work involved.
Hah! heat work. I once fired some pieces for another potter, his glaze,
his clay.
In his gas kiln fired for 6 hours to Cone 9, glassy celadon type glaze
over cement grey body.
In my wood kiln fired over 36 hours to Cone 10, luscious, frosty white
satin on dark, toasty body.
Des
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Craig Martell on tue 28 mar 06
Des responded:
>Trying Sam's recipe again at a higher cone is definitely a thought.
Hello Des:
I was thinking, after my last post, that you could probably recalculate
Sam's recipe with the correct spar, FPR200. This could quite possibly put
everything in the right bag. I used the analysis for Australian Potash
Spar and this may have been the whole problem. I don't, as yet, have the
analysis for FPR200 or I would redo the formula.
regards, Craig Martell Hopewell, Oregon
Sam Kelly on wed 29 mar 06
So what if I was to fire higher, any clues as to the expected outcome?
I have been using this glaze for 3 years so in any of you crack it, you
should be able to reproduce no worries.
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