Ann Brink on tue 2 jan 07
Are you sure that is the correct amount of Manganese Dioxide? sounds like
waaaay to much...maybe it should be 2.0? From my experience w/ mang. diox.
you would get a strong brownish purple with bubbles, using that amount.
Ann Brink in Lompoc CA
(mostly about pottery)
----- Original Message -----
From: "Stephanie Wright"
> Happy 2007, everyone! I have a glaze recipe called Apple Blossom, that is
> used at Clemson University. The recipe is as follows:
>
> Potash Feldspar 40
> Flint 30
> Whiting 20
> Kaolin (EPK) 10
> Manganese Dioxide 20
> Copper Oxide 7.5
>
> The person who posted it on the glaze database describes it as (and I
> quote) "Nice clear rose in most firings, but temperature fluctuations can
> opacify the glaze and give a strong dense pink to mauve. Clear to grey
> where very thin. Glaze tends to craze rather a lot where thick."
>
> I was thinking I might be able to tweak this recipe by combining it (sort
> of) with a base I already know works beautifully. My aim here is to keep
> the color pretty much as described, while getting rid of the crazing. I
> should add that I have use of a gas kiln, and pieces are fired ^10R. Do
> you think the following changes would work?
>
> Custer Feldspar 54.65
> Whiting 2.36
> Bone Ash 6.59
> Kaolin 14.10
> Silica 18.30
> Dolomite 2.17
> Zinc Oxide 1.83
> Manganese Dioxide 20
> Copper Oxide 7.5
>
> Thanks in advance for your comments/opinions!
>
> Stephanie
>
Timothy Sullivan on tue 2 jan 07
These are two very different base glazes.
This looks like a variation on the classic 40/30/20/10 glaze with the silica
and spar amounts swapped.
Potash Felds 40.00 CaO 0.76* Exp 7.08
Silica 30.00 K2O 0.16* Si:Al 9.94
Whiting 20.00 Na2O 0.07*
Kaolin (EPK) 10.00 Al2O3 0.40
SiO2 3.94
Your proposed base
Silica 18.30 CaO 0.45* Exp 6.95
Whiting 2.36 MgO 0.06* Si:Al 6.98
K2O 0.26*
Custer Felds 54.65 Na2O 0.12*
Bone Ash 6.59 ZnO 0.10*
Kaolin 14.10 TiO2 0.01
Dolomite 2.17 Al2O3 0.68
Zinc Oxide 1.83 SiO2 4.74
P2O5 0.09
I would think that 20% manganese diox and 7.5% copper oxide is a strange
combo for a clear rose in any glaze.
It seems to me that you should test the original glaze as is, and see if it
crazes on your body, and if you get the color as described.
Timothy Sullivan
Creekside Pottery
www.creeksidepottery.net
Marietta, GA
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Stephanie
Wright
Sent: Tuesday, January 02, 2007 6:53 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Tweaking a glaze recipe - opinions/help needed
Happy 2007, everyone! I have a glaze recipe called Apple Blossom, that is
used at Clemson University. The recipe is as follows:
Potash Feldspar 40
Flint 30
Whiting 20
Kaolin (EPK) 10
Manganese Dioxide 20
Copper Oxide 7.5
The person who posted it on the glaze database describes it as (and I
quote) "Nice clear rose in most firings, but temperature fluctuations can
opacify the glaze and give a strong dense pink to mauve. Clear to grey
where very thin. Glaze tends to craze rather a lot where thick."
I was thinking I might be able to tweak this recipe by combining it (sort
of) with a base I already know works beautifully. My aim here is to keep
the color pretty much as described, while getting rid of the crazing. I
should add that I have use of a gas kiln, and pieces are fired ^10R. Do
you think the following changes would work?
Custer Feldspar 54.65
Whiting 2.36
Bone Ash 6.59
Kaolin 14.10
Silica 18.30
Dolomite 2.17
Zinc Oxide 1.83
Manganese Dioxide 20
Copper Oxide 7.5
Thanks in advance for your comments/opinions!
Stephanie
____________________________________________________________________________
__
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Stephanie Wright on tue 2 jan 07
Happy 2007, everyone! I have a glaze recipe called Apple Blossom, that is
used at Clemson University. The recipe is as follows:
Potash Feldspar 40
Flint 30
Whiting 20
Kaolin (EPK) 10
Manganese Dioxide 20
Copper Oxide 7.5
The person who posted it on the glaze database describes it as (and I
quote) "Nice clear rose in most firings, but temperature fluctuations can
opacify the glaze and give a strong dense pink to mauve. Clear to grey
where very thin. Glaze tends to craze rather a lot where thick."
I was thinking I might be able to tweak this recipe by combining it (sort
of) with a base I already know works beautifully. My aim here is to keep
the color pretty much as described, while getting rid of the crazing. I
should add that I have use of a gas kiln, and pieces are fired ^10R. Do
you think the following changes would work?
Custer Feldspar 54.65
Whiting 2.36
Bone Ash 6.59
Kaolin 14.10
Silica 18.30
Dolomite 2.17
Zinc Oxide 1.83
Manganese Dioxide 20
Copper Oxide 7.5
Thanks in advance for your comments/opinions!
Stephanie
Ivor and Olive Lewis on wed 3 jan 07
Dear Stephanie Wright,=20
Crazing is a function of the relationship between you clay body and the =
glaze that is put over it.
If you start to combine two glazes you introduce more variables and =
reduce your control over the situation.
Go back to basics. Ask questions about the cause of 4-3-2-1 crazing =
then try out proven ways of exercising control as described by Frank =
Hamer or Cooper and Royle.
By the way, 20% Manganese Dioxide is an enormous quantity dissolve in a =
glaze. I would expect a dark metallic pewter, not what you say you are =
getting.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on thu 4 jan 07
Hi Stephanie,
The glaze itself looks like a stable glaze but with that much colouring
oxide it's just going to be black metal all over the surface - those
numbers for copper and manganese are just wrong.
The expansion of your revision is just about the same as the original -
don't increase spar if you want to lower expansion.
Alumina is way up in your revision and silica is up and the ration between
them has changed a lot - so it's just not the same looking glaze - and may
not melt enough at cone 10.
Adding zinc oxide to a reduction glaze is probably a waste of time as it is
easily reduced and vaporizes during a reduction firing.
You need to tell us what cone you are firing to and oxidation or reduction.
RR
>Potash Feldspar 40
>Flint 30
>Whiting 20
>Kaolin (EPK) 10
>Manganese Dioxide 20
>Copper Oxide 7.5
>
>The person who posted it on the glaze database describes it as (and I
>quote) "Nice clear rose in most firings, but temperature fluctuations can
>opacify the glaze and give a strong dense pink to mauve. Clear to grey
>where very thin. Glaze tends to craze rather a lot where thick."
>
>I was thinking I might be able to tweak this recipe by combining it (sort
>of) with a base I already know works beautifully. My aim here is to keep
>the color pretty much as described, while getting rid of the crazing. I
>should add that I have use of a gas kiln, and pieces are fired ^10R. Do
>you think the following changes would work?
>
>Custer Feldspar 54.65
>Whiting 2.36
>Bone Ash 6.59
>Kaolin 14.10
>Silica 18.30
>Dolomite 2.17
>Zinc Oxide 1.83
>Manganese Dioxide 20
>Copper Oxide 7.5
>
>Thanks in advance for your comments/opinions!
>
>Stephanie
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Timothy Sullivan on thu 4 jan 07
Ron -
" Adding zinc oxide to a reduction glaze is probably a waste of time as it
is easily reduced and vaporizes during a reduction firing."
This brings up an interesting point - you see zinc ox in an awful lot of
reduction glazes, particularly copper reds. Is it possible that the purpose
of the zinc is to stimulate an early melt for an early reduction? Sort of
like using a frit for the same reason.
Not relevant to the glaze in question, but interesting in itself.
Timothy Sullivan
Creekside Pottery
www.creeksidepottery.net
Marietta, GA
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ron Roy
Sent: Thursday, January 04, 2007 2:52 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Tweaking a glaze recipe - opinions/help needed
Hi Stephanie,
The glaze itself looks like a stable glaze but with that much colouring
oxide it's just going to be black metal all over the surface - those
numbers for copper and manganese are just wrong.
The expansion of your revision is just about the same as the original -
don't increase spar if you want to lower expansion.
Alumina is way up in your revision and silica is up and the ration between
them has changed a lot - so it's just not the same looking glaze - and may
not melt enough at cone 10.
Adding zinc oxide to a reduction glaze is probably a waste of time as it is
easily reduced and vaporizes during a reduction firing.
You need to tell us what cone you are firing to and oxidation or reduction.
RR
>Potash Feldspar 40
>Flint 30
>Whiting 20
>Kaolin (EPK) 10
>Manganese Dioxide 20
>Copper Oxide 7.5
>
>The person who posted it on the glaze database describes it as (and I
>quote) "Nice clear rose in most firings, but temperature fluctuations can
>opacify the glaze and give a strong dense pink to mauve. Clear to grey
>where very thin. Glaze tends to craze rather a lot where thick."
>
>I was thinking I might be able to tweak this recipe by combining it (sort
>of) with a base I already know works beautifully. My aim here is to keep
>the color pretty much as described, while getting rid of the crazing. I
>should add that I have use of a gas kiln, and pieces are fired ^10R. Do
>you think the following changes would work?
>
>Custer Feldspar 54.65
>Whiting 2.36
>Bone Ash 6.59
>Kaolin 14.10
>Silica 18.30
>Dolomite 2.17
>Zinc Oxide 1.83
>Manganese Dioxide 20
>Copper Oxide 7.5
>
>Thanks in advance for your comments/opinions!
>
>Stephanie
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
____________________________________________________________________________
__
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.
Stephanie Wright on thu 4 jan 07
Mr. Roy,
Thank you for your response. I think those of you that replied are correct
about there being too much colorant. The person who posted it on the
database must have made a typo. I am going to lower the Manganese to 2. I
am firing in a gas kiln, ^10R.
My instructor is a wonderful man (Mr. Renzo Faggioli), and extremely
talented, but he tends to like alot of earthy and muted tones in his
glazes. We have mostly those types of colors for use in the classroom.
However he is encouraging me by letting me find and test some brighter
glazes, so I can learn more about that aspect of creating pottery. I know
alot of brighter colors tend to fade out when doing ^10R, but there must
be some that survive! :-)
Besides what I had put forth in my original posting on this, I also had
the thought to try sort of a 'modified' Leach-type formula, using the
addition of Dolomite to prevent crazing. Do you think the following might
work?
Custer Feldspar 42.5
Silica 25
Whiting 20
Kaolin 10
Dolomite 2.5
Manganese Dioxide 2
Copper Oxide 7.5
As an aside, Mr. Roy, I must tell you that I admire your work VERY much!
Thanks (to all) for the help!
Stephanie
Bonnie Staffel on thu 4 jan 07
About this glaze, perhaps the word, Manganese, was mistaken for Magnesium
which I believe alters colors in a glaze without producing one of its own.
I am no chemist, just thinking common sense as this error has cropped up in
my own life when testing glazes. With Magnesium being so light in weight,
though, 20 would really create a lot of volume. So perhaps I am way off
base here, just thinking like a cook, sideways thinker and proof reader.
Regards,
Bonnie Staffel
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD Throwing with Coils and Slabs
DVD Beginning Processes
Charter Member Potters Council
Ron Roy on fri 5 jan 07
Hi Timothy,
In most cases - when you fire one of those glazes without the zinc oxide
you will find no difference.
David Hendly did a bunch of them and wrote an article for CM - I saw the
tests - I could see no difference.
In some cases - probably when a glaze seals over enough before reduction
starts - the zinc will have some effect - perhaps glazes with boron in?
It's also probably the reason zinc oxide has a reputation for producing
pinholes in lower and mid fire ranges - there is usually some reduction
present in those firing at some stages - the zinc is easily reduced to the
metal- and boils about 900C - not sure about that temperature.
It's probably why the recommendation was - a little zinc is OK (2%) but
more can lead to pinholing.
RR
>Ron -
>" Adding zinc oxide to a reduction glaze is probably a waste of time as it
>is easily reduced and vaporizes during a reduction firing."
>
>This brings up an interesting point - you see zinc ox in an awful lot of
>reduction glazes, particularly copper reds. Is it possible that the purpose
>of the zinc is to stimulate an early melt for an early reduction? Sort of
>like using a frit for the same reason.
>
>Not relevant to the glaze in question, but interesting in itself.
>
>Timothy Sullivan
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ron Roy on fri 5 jan 07
Hi Stephanie,
You actually raised the expansion of the original - the way to do it is
lower the KNaO and replace with MgO - thats one way - replacing the KNaO
with Li2O using spodumene would also work.
You want to keep the silica alumina ratio the same and keep the amounts of
silica and alumina the same to have the best chance of keeping the glaze
the same. In this case the Li2O would be the best because of the colour you
are looking for. Not sure if you have any spodumene or petalite or such -
if you do tell me and I'll send a revision using them.
In the meantime here is a revision using more MgO.
By the way the Copper is still way to high try it at 0.75
I used talc because dolomite is a variable material - yours may be
different than mine. I can still do it with dolomite if you like.
Custer - 27.0
Whiting - 18.0
Talc - 4.5
EPK - 16.5
Silica - 34.0
Total 100.0
Let me know if you want me to do one with Li2O.
If you want to be able to deal with glazes I suggest you consider getting a
glaze calc program - takes most of the guess work out of it.
How do you know about my work?
RR
>Mr. Roy,
>
>Thank you for your response. I think those of you that replied are correct
>about there being too much colorant. The person who posted it on the
>database must have made a typo. I am going to lower the Manganese to 2. I
>am firing in a gas kiln, ^10R.
>
>My instructor is a wonderful man (Mr. Renzo Faggioli), and extremely
>talented, but he tends to like alot of earthy and muted tones in his
>glazes. We have mostly those types of colors for use in the classroom.
>However he is encouraging me by letting me find and test some brighter
>glazes, so I can learn more about that aspect of creating pottery. I know
>alot of brighter colors tend to fade out when doing ^10R, but there must
>be some that survive! :-)
>
>Besides what I had put forth in my original posting on this, I also had
>the thought to try sort of a 'modified' Leach-type formula, using the
>addition of Dolomite to prevent crazing. Do you think the following might
>work?
>
>Custer Feldspar 42.5
>Silica 25
>Whiting 20
>Kaolin 10
>Dolomite 2.5
>Manganese Dioxide 2
>Copper Oxide 7.5
>
>
>As an aside, Mr. Roy, I must tell you that I admire your work VERY much!
>
>Thanks (to all) for the help!
>
>Stephanie
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Bruce Girrell on fri 5 jan 07
Timothy Sullivan wrote:
> This brings up an interesting point - you see zinc ox in an awful lot of
> reduction glazes, particularly copper reds. Is it possible that
> the purpose
> of the zinc is to stimulate an early melt for an early reduction? Sort of
> like using a frit for the same reason.
Perhaps, but if it does, it appears to have no effect on the result. David
Hendley wrote an article for Ceramics Monthly (Oct 1999) about the use of
zinc and barium in copper red recipes. An abbreviated version of the article
can be read at http://www.ceramicsmonthly.org/mustreads/simplyred.asp.
Hendley concludes that the addition of zinc and/or barium contributes
nothing to the copper red results. Unfortunately, the abbreviated version
does not include any photos of the results. You might see if you can find a
copy of the original.
Bruce Girrell
Timothy Sullivan on fri 5 jan 07
Expansion actually gets worse when you increase the feldspar and decrease
the silica. It would work better to add silica. I'm still not convinced
that you will get the color you want. 7.5% copper is a lot of copper.
I think that you should test for color first, and only after you can get the
color that you want should you fix any crazing issue.
Tim
Timothy Sullivan
Creekside Pottery
www.creeksidepottery.net
Marietta, GA
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Stephanie
Wright
Sent: Thursday, January 04, 2007 5:51 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Tweaking a glaze recipe - opinions/help needed
Mr. Roy,
Thank you for your response. I think those of you that replied are correct
about there being too much colorant. The person who posted it on the
database must have made a typo. I am going to lower the Manganese to 2. I
am firing in a gas kiln, ^10R.
My instructor is a wonderful man (Mr. Renzo Faggioli), and extremely
talented, but he tends to like alot of earthy and muted tones in his
glazes. We have mostly those types of colors for use in the classroom.
However he is encouraging me by letting me find and test some brighter
glazes, so I can learn more about that aspect of creating pottery. I know
alot of brighter colors tend to fade out when doing ^10R, but there must
be some that survive! :-)
Besides what I had put forth in my original posting on this, I also had
the thought to try sort of a 'modified' Leach-type formula, using the
addition of Dolomite to prevent crazing. Do you think the following might
work?
Custer Feldspar 42.5
Silica 25
Whiting 20
Kaolin 10
Dolomite 2.5
Manganese Dioxide 2
Copper Oxide 7.5
As an aside, Mr. Roy, I must tell you that I admire your work VERY much!
Thanks (to all) for the help!
Stephanie
____________________________________________________________________________
__
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.
Ron Roy on fri 5 jan 07
Hi Bonnie,
Magnesium carb is a flux starting about cone 4 so I would expect this
glaze to be way overfired at cone 10 and short of both alumina and silica.
On the other hand the expansion is lowered o it might not craze - and
because MgO is such a stiffner in glazes - the glaze may not run off the
pot - perhaps worth a test.
Protect any kiln shelves though - cause it's going to crawl.
Not hard to do the same glaze with talc though - it would not crawl.
I'm getting a kiln redady to fire - I think I'll try try the Talc version.
RR
>About this glaze, perhaps the word, Manganese, was mistaken for Magnesium
>which I believe alters colors in a glaze without producing one of its own.
>I am no chemist, just thinking common sense as this error has cropped up in
>my own life when testing glazes. With Magnesium being so light in weight,
>though, 20 would really create a lot of volume. So perhaps I am way off
>base here, just thinking like a cook, sideways thinker and proof reader.
>
>Regards,
>
>Bonnie Staffel
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ivor and Olive Lewis on sat 6 jan 07
Dear Timothy Sullivan,=20
You pose a rather interesting philosophical scientific proposition
of reduction glazes, particularly copper reds. Is it possible that the =
purpose of the zinc is to stimulate an early melt for an early =
reduction? Sort of like using a frit for the same reason.>
It would be interesting to interrogate the originators of published =
recipes that include Zinc Oxide as an ingredient for mixtures that will =
be fired in reduction. We need to ask them why did they do it? I am sure =
there enough examples around from which to choose.
Concerning you second proposition. Most frits begin to melt at the =
"Glass Transition Point", a temperature that can be found using a =
dilatometer as illustrated in Ron Roys graphs in MC6G. Zinc oxide has a =
melting point in the region of 1975 deg C (3587 deg F). Assuming it is =
possible for Zinc oxide to react with one of the glaze ingredients, say =
Silica, the resulting compound is rather refractory, melting above 1500 =
deg C ( >2732 F). But if reduction is needed to encourage copper red =
early fusion would be counterproductive, restricting the diffusion of =
carbon monoxide into an impenetrable surface.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on sat 6 jan 07
Dear Bonnie Staffel,
True, Manganese can be erroneously used instead of Magnesium. I have =
even seen this done in a standard reference textbook, but in the reverse =
sense.
But in this case the original recipe had four main ingredients which had =
a total of 100 so it is more likely to be a typo.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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