Kathy Maves on tue 20 nov 01
Hi,
I've been working on developing an iron red, or
indian red, cone 6 glaze off my usual base and have
met a few bumps.
Why is it that I cannot sub Zircopax for the tin
that most recipes call for? Is tin not behaving as an
opacifier in this instance? What makes tin so
special? Also, I've read that adding 1-3% bone ash
helps, and have mixed up a few tests, will fire
tomorrow. Why bone ash? Some of the recipes I've
reviewed used a significant amount of barium, which I
usually avoid. As far as I know, it's not necessary,
anyone know different?
I've noticed that most iron red recipes are similar,
but they just seem weird. They don't make sense to me
yet. Any ideas? You can respond off-list if you'd
prefer --- kathymaves@yahoo.com
Thanks Tons,
Kathy
Wishing I was seeing red in Wisconsin
__________________________________________________
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Paul Lewing on wed 21 nov 01
Kathy, I've done innumerable tests trying to get a good oxidation iron red
also. I would agree with everything Chris said about them, and add one
other tip. The redder the iron you use is before it's fired, the redder it
will be after. I've tried many of the same recipes with many different
brands and strengths of iron oxide, and you want the stuff that's really
bright orange-red when it's raw.
I don't know why tin works better than zirconium in this glaze, or why the
phosphorous in the bone ash helps in the development of this color, but I do
know those are both true.
Paul Lewing, Seattle
Christena Schafale on wed 21 nov 01
Kathy,
As one who took on cone 6 iron red as my first major project when learning
to mix glazes (oh the optimism of the naive...my second project was
reformulating floating blue...), I can tell you that "developing an iron
red... off [your] usual base" is most likely not going to work.
I tested at least 12 different glazes and variations before I got something
red instead of s--t brown. Iron reds for cone 6 are a very peculiar
animal, which is why those recipes you are finding look so odd. These
glazes rely on the formation of iron crystals in the cooling phase of
firing, and in order to get the crystals you have to have a certain glaze
chemistry. In particular, these glazes must have so little alumina that
any other glaze would run right off the pot. Silica:alumina ratios are
typically around 15 or more, if I remember right, and the silica AND
alumina are way below the limit formulas. If you do computer glaze
calculation, and if you try to keep the glaze within the recommended
limits, you will get brown, not red. Been there, done that.
As for the tin, I don't know why it helps, but it isn't just the
opacification that is at work there. Same for the bone ash -- possibly
it's the phosphorus content that the bone ash brings, but I don't know. I
do know that the only iron reds that I was successful with contained bone
ash, and it seemed to be the magic ingredient (along with high calcium,
some magnesium, some boron, and extremely low alumina). I used a good deal
more bone ash than you mention.
Here's the recipe I came up with, along with my comments when I posted it
to Clayart a couple of years ago:
=========
KT 1-4 BALL CLAY.... 11.00
SILICA.............. 34.00
G-200 FELDSPAR G200. 11.00
GERSTLEY BORATE..... 11.00
TALC................ 11.00
DOLOMITE............ 11.00
BONE ASH............ 11.00
IRON OXIDE RED...... 11.00
========
111.00
CaO 0.43* 11.08%
MgO 0.32* 6.01%
K2O 0.03* 1.26%
Na2O 0.05* 1.38%
TiO2 0.00 0.16%
Al2O3 0.11 5.43%
B2O3 0.18* 5.65%
P2O5 0.08 4.95%
SiO2 1.92 53.39%
Fe2O3 0.14 10.68%
Cost/kg 0.42
Si:Al 16.68
SiB:Al 18.20
Expan 6.49
Tested it, and it is actually red. Not bright shiny tomato red, mind you,
but a soft, darkish red-brown matt. Nonetheless I was thrilled. I fired it
to cone 6, on the Slow schedule on my Skutt KM1027, with a 30 minute hold
and no special cooling at all. I have not tried it on a slower schedule
with extended cooling. I tried varying amounts of RIO, and actually, more
RIO makes this glaze blacker rather than redder. A somewhat thin coat seems
to work better than a thick one -- it's sort of brown-green-gold where it's
thick. Examined under 30x magnification, it's a near-solid field of sparkly
red crystals -- very cool. I tried the refire-to-bisque temp trick, and it
doesn't get any redder -- perhaps it has all the iron crystals it can hold
already.
Now, Ron Roy will take one look at the analysis and tell you it's dreadful.
The alumina is very low and the silica is pretty low. It's oversupplied
with magnesium. On the other hand, it doesn't run (at least hasn't yet),
doesn't craze or shiver, is unaffected by soaking in either vinegar or
dishwashing detergent for 3 days, and passes the freeze/boil test. All
there is in it to leach is iron. So I hesitantly conclude that it's
probably food-safe, though I can't speak to it's durability under daily use
-- I was able to mark it with a steak knife, so you might not want to put
it on dinner plates. >
Here's another one, which is the result of dumping all my failed tests
together and line-blending the result with Chris Red, above. I actually
ended up liking this one better, as it was a little less matt, though not
shiny, and seemed more durable. The amounts are weird and there are so
many ingredients because it was a mix of so many different recipes. You'll
notice that I did manage to get the silica into a more normal range, though
the alumina is still quite low. The expansion is very low, but I never had
any problem with shivering with this glaze, possibly because of all the
iron, Ron said at the time.
IMCR 6040 (Burgundy Satin)
==============================
EPK KAOLIN.......... 4.25
KT 1-4 BALL CLAY.... 5.90
SILICA.............. 31.60
GERSTLEY BORATE .. 16.00
G 200 FELDSPAR...... 4.50
CUSTER FELDSPAR..... 2.00
F-4 FELDSPAR........ 11.50
TALC................ 9.00
DOLOMITE............ 7.75
WHITING............. 0.90
BONE ASH............ 6.60
SPANISH RED IRON OX. 13.00
========
113.00
CaO 0.50* 10.51%
MgO 0.38* 5.76%
K2O 0.04* 1.51%
Na2O 0.08* 1.88%
TiO2 0.00 0.12%
Al2O3 0.21 7.89%
B2O3 0.21 5.51%
P2O5 0.06 3.37%
SiO2 2.79 63.12%
Fe2O3 0.01 0.33%
Si:Al 13.57
SiB:Al 14.60
Expan 5.87
By the way, this is one of those glazes that changes color as it cools,
even at fairly low temps. Several times, I peeked in the kiln at my usual
over-eager 200C and was crushed to find dark chocolate brown pots instead
of the Indian red I was hoping for. But by the next morning when I
actually unloaded, the pots were red.
Have fun, and feel free to email back on or off list if you have questions.
Chris Schafale
At 11:56 PM 11/20/01 -0800, you wrote:
>Hi,
> I've been working on developing an iron red, or
>indian red, cone 6 glaze off my usual base and have
>met a few bumps.
> Why is it that I cannot sub Zircopax for the tin
>that most recipes call for? Is tin not behaving as an
>opacifier in this instance? What makes tin so
>special? Also, I've read that adding 1-3% bone ash
>helps, and have mixed up a few tests, will fire
>tomorrow. Why bone ash? Some of the recipes I've
>reviewed used a significant amount of barium, which I
>usually avoid. As far as I know, it's not necessary,
>anyone know different?
> I've noticed that most iron red recipes are similar,
>but they just seem weird. They don't make sense to me
>yet. Any ideas? You can respond off-list if you'd
>prefer --- kathymaves@yahoo.com
>
>Thanks Tons,
>Kathy
>Wishing I was seeing red in Wisconsin
Consultation and Referral Specialist
Resources for Seniors
christenas@rfsnc.org
www.resourcesforseniors.com
Phone: (919) 713-1537
FAX: (919) 872-9574
1110 Navaho Dr, Suite 400
Raleigh, NC 27609
Steve Mills on thu 22 nov 01
Kathy,
Take a good look at Mike Bailey's book on cone 6 glazes; he has a whole
chapter (15) on iron reds.
Glazes Cone 6
Michael Bailey
Pub. by A & C Black (UK)
University of Pennsylvania Press (USA)
Steve
shamelessly plugging my work partners excellent book in
Bath
UK
In message , Kathy Maves writes
>Hi,
> I've been working on developing an iron red, or
>indian red, cone 6 glaze off my usual base and have
>met a few bumps.
> Why is it that I cannot sub Zircopax for the tin
>that most recipes call for? Is tin not behaving as an
>opacifier in this instance? What makes tin so
>special? Also, I've read that adding 1-3% bone ash
>helps, and have mixed up a few tests, will fire
>tomorrow. Why bone ash? Some of the recipes I've
>reviewed used a significant amount of barium, which I
>usually avoid. As far as I know, it's not necessary,
>anyone know different?
> I've noticed that most iron red recipes are similar,
>but they just seem weird. They don't make sense to me
>yet. Any ideas? You can respond off-list if you'd
>prefer --- kathymaves@yahoo.com
>
>Thanks Tons,
>Kathy
>Wishing I was seeing red in Wisconsin
>
>__________________________________________________
>Do You Yahoo!?
>Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month.
>http://geocities.yahoo.com/ps/info1
--
Steve Mills
Bath
UK
Paul Taylor on thu 22 nov 01
Dear Christina and all
A model post and A great help to me since i am hoping to work on an iron
red cone 9 but your formulas will contain the basic principles for me to
work on . If you have some formulas for cone ( or any other suggestions)
please post them to me.
There is another method that Cardew suggests at cone 9 but that is more of
a shino . It has no calcium or magnesium and requires making a potash frit
or trying to get soluble salts (potassium carbonate) on to the pot. If any
body has any experience or any tricks for doing the latter and keeping the
glaze intact please tell.
Also what to use as a crucible. if any body has a suggestion or
experience in making frit in a studio setting I would be grateful.
Regards from Paul Taylor
http://www.anu.ie/westportpottery
Alchemy is the proof that economics is not a science.
> From: Christena Schafale
> Reply-To: Ceramic Arts Discussion List
> Date: Wed, 21 Nov 2001 09:20:16 -0500
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Understanding iron reds
>
> Kathy,
>
> As one who took on cone 6 iron red as my first major project when learning
> to mix glazes (oh the optimism of the naive...my second project was
> reformulating floating blue...), I can tell you that "developing an iron
> red... off [your] usual base" is most likely not going to work.
>
> I tested at least 12 different glazes and variations before I got something
> red instead of s--t brown. Iron reds for cone 6 are a very peculiar
> animal, which is why those recipes you are finding look so odd. These
> glazes rely on the formation of iron crystals in the cooling phase of
> firing, and in order to get the crystals you have to have a certain glaze
> chemistry. In particular, these glazes must have so little alumina that
> any other glaze would run right off the pot. Silica:alumina ratios are
> typically around 15 or more, if I remember right, and the silica AND
> alumina are way below the limit formulas. If you do computer glaze
> calculation, and if you try to keep the glaze within the recommended
> limits, you will get brown, not red. Been there, done that.
>
> As for the tin, I don't know why it helps, but it isn't just the
> opacification that is at work there. Same for the bone ash -- possibly
> it's the phosphorus content that the bone ash brings, but I don't know. I
> do know that the only iron reds that I was successful with contained bone
> ash, and it seemed to be the magic ingredient (along with high calcium,
> some magnesium, some boron, and extremely low alumina). I used a good deal
> more bone ash than you mention.
>
> Here's the recipe I came up with, along with my comments when I posted it
> to Clayart a couple of years ago:
>
> > =========
> KT 1-4 BALL CLAY.... 11.00
> SILICA.............. 34.00
> G-200 FELDSPAR G200. 11.00
> GERSTLEY BORATE..... 11.00
> TALC................ 11.00
> DOLOMITE............ 11.00
> BONE ASH............ 11.00
> IRON OXIDE RED...... 11.00
> ========
> 111.00
> CaO 0.43* 11.08%
> MgO 0.32* 6.01%
> K2O 0.03* 1.26%
> Na2O 0.05* 1.38%
> TiO2 0.00 0.16%
> Al2O3 0.11 5.43%
> B2O3 0.18* 5.65%
> P2O5 0.08 4.95%
> SiO2 1.92 53.39%
> Fe2O3 0.14 10.68%
> Cost/kg 0.42
> Si:Al 16.68
> SiB:Al 18.20
> Expan 6.49
> Tested it, and it is actually red. Not bright shiny tomato red, mind you,
> but a soft, darkish red-brown matt. Nonetheless I was thrilled. I fired it
> to cone 6, on the Slow schedule on my Skutt KM1027, with a 30 minute hold
> and no special cooling at all. I have not tried it on a slower schedule
> with extended cooling. I tried varying amounts of RIO, and actually, more
> RIO makes this glaze blacker rather than redder. A somewhat thin coat seems
> to work better than a thick one -- it's sort of brown-green-gold where it's
> thick. Examined under 30x magnification, it's a near-solid field of sparkly
> red crystals -- very cool. I tried the refire-to-bisque temp trick, and it
> doesn't get any redder -- perhaps it has all the iron crystals it can hold
> already.
>
> Now, Ron Roy will take one look at the analysis and tell you it's dreadful.
> The alumina is very low and the silica is pretty low. It's oversupplied
> with magnesium. On the other hand, it doesn't run (at least hasn't yet),
> doesn't craze or shiver, is unaffected by soaking in either vinegar or
> dishwashing detergent for 3 days, and passes the freeze/boil test. All
> there is in it to leach is iron. So I hesitantly conclude that it's
> probably food-safe, though I can't speak to it's durability under daily use
> -- I was able to mark it with a steak knife, so you might not want to put
> it on dinner plates. >
>
> Here's another one, which is the result of dumping all my failed tests
> together and line-blending the result with Chris Red, above. I actually
> ended up liking this one better, as it was a little less matt, though not
> shiny, and seemed more durable. The amounts are weird and there are so
> many ingredients because it was a mix of so many different recipes. You'll
> notice that I did manage to get the silica into a more normal range, though
> the alumina is still quite low. The expansion is very low, but I never had
> any problem with shivering with this glaze, possibly because of all the
> iron, Ron said at the time.
>
> IMCR 6040 (Burgundy Satin)
> ==============================
> EPK KAOLIN.......... 4.25
> KT 1-4 BALL CLAY.... 5.90
> SILICA.............. 31.60
> GERSTLEY BORATE .. 16.00
> G 200 FELDSPAR...... 4.50
> CUSTER FELDSPAR..... 2.00
> F-4 FELDSPAR........ 11.50
> TALC................ 9.00
> DOLOMITE............ 7.75
> WHITING............. 0.90
> BONE ASH............ 6.60
> SPANISH RED IRON OX. 13.00
> ========
> 113.00
> CaO 0.50* 10.51%
> MgO 0.38* 5.76%
> K2O 0.04* 1.51%
> Na2O 0.08* 1.88%
> TiO2 0.00 0.12%
> Al2O3 0.21 7.89%
> B2O3 0.21 5.51%
> P2O5 0.06 3.37%
> SiO2 2.79 63.12%
> Fe2O3 0.01 0.33%
> Si:Al 13.57
> SiB:Al 14.60
> Expan 5.87
>
> By the way, this is one of those glazes that changes color as it cools,
> even at fairly low temps. Several times, I peeked in the kiln at my usual
> over-eager 200C and was crushed to find dark chocolate brown pots instead
> of the Indian red I was hoping for. But by the next morning when I
> actually unloaded, the pots were red.
>
> Have fun, and feel free to email back on or off list if you have questions.
>
> Chris Schafale
>
> At 11:56 PM 11/20/01 -0800, you wrote:
>> Hi,
>> I've been working on developing an iron red, or
>> indian red, cone 6 glaze off my usual base and have
>> met a few bumps.
>> Why is it that I cannot sub Zircopax for the tin
>> that most recipes call for? Is tin not behaving as an
>> opacifier in this instance? What makes tin so
>> special? Also, I've read that adding 1-3% bone ash
>> helps, and have mixed up a few tests, will fire
>> tomorrow. Why bone ash? Some of the recipes I've
>> reviewed used a significant amount of barium, which I
>> usually avoid. As far as I know, it's not necessary,
>> anyone know different?
>> I've noticed that most iron red recipes are similar,
>> but they just seem weird. They don't make sense to me
>> yet. Any ideas? You can respond off-list if you'd
>> prefer --- kathymaves@yahoo.com
>>
>> Thanks Tons,
>> Kathy
>> Wishing I was seeing red in Wisconsin
>
> Consultation and Referral Specialist
> Resources for Seniors
> christenas@rfsnc.org
> www.resourcesforseniors.com
> Phone: (919) 713-1537
> FAX: (919) 872-9574
> 1110 Navaho Dr, Suite 400
> Raleigh, NC 27609
>
> ______________________________________________________________________________
> 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.
Diana Pancioli on fri 23 nov 01
I also recommend the Baily book, but not just for iron reds. We will be
using it next semester as a text for an independent study on glazes. The
book is concise, clear, and well organized. (and I don't know Mr. Bailey.)
Why use tin in copper reds? Because tin is a material that assists
reduction. The gurus can tell us why. It has something to do with tin being
"amphoteric" (if I am remembering the word correctly).
Diana
Ron Roy on sun 25 nov 01
Hi Kathy,
Tin brings out the reddish tones of iron - you are right - zirconium
silicate doesn't cut it.
I don't know why P203 (in Bone ash and Tricalcium phosphate) helps - it
produces bubbles and a bluish tinge in some glazes but I don't know why
that would help. Perhaps a clue would be how bubbles affect colour - the
size of the bubbles determines which colours are reflected.
I don't know what kind of glaze you are talking about but if it's a matte
iron red - it relies on OXIDIZED crystals of iron on the surface of the
glaze - the better oxidized the iron is the redder it will be - fire bisque
slow and provide lots of oxygen - and fire a hard bisque. Slow cooling
helps this kind of glaze. Redish Shino glazes would be an example of iron
on the surface giving colour. Slow cooling will make it stronger as will
striking.
The shiney reds from iron I don't know much about but again - oxidized iron
oxide is red - the better it's oxidized the redder it is. Iron oxide easliy
reduced so it can be affected by even the materials in a glaze while it's
melting.
Barium is not necessary - in fact Strontium probably gives better colour
with iron. CaO tends to bleach iron so you will probably find that
minimized in many iron red glazes.
Good section on iron in glazes in the Hamer book by the way.
You are right - iron reds - well many of them - are odd - it is because the
red only develops when the conditions are right.
RR
> I've been working on developing an iron red, or
>indian red, cone 6 glaze off my usual base and have
>met a few bumps.
> Why is it that I cannot sub Zircopax for the tin
>that most recipes call for? Is tin not behaving as an
>opacifier in this instance? What makes tin so
>special? Also, I've read that adding 1-3% bone ash
>helps, and have mixed up a few tests, will fire
>tomorrow. Why bone ash? Some of the recipes I've
>reviewed used a significant amount of barium, which I
>usually avoid. As far as I know, it's not necessary,
>anyone know different?
> I've noticed that most iron red recipes are similar,
>but they just seem weird. They don't make sense to me
>yet. Any ideas? You can respond off-list if you'd
>prefer --- kathymaves@yahoo.com
>
>Thanks Tons,
>Kathy
>Wishing I was seeing red in Wisconsin
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Des & Jan Howard on sun 25 nov 01
Paul Lewing wrote:
> The redder the iron you use is before it's fired, the redder it
> will be after. I've tried many of the same recipes with many different
> brands and strengths of iron oxide, and you want the stuff that's really
> bright orange-red when it's raw.
I have found that any iron oxide, black/purple/yellow/reddish,
ends up orange-red after it is bisque fired.
> I don't know why tin works better than zirconium in this glaze, or why the
> phosphorous in the bone ash helps in the development of this color, but I do
> know those are both true.
The tomato red glaze prefers a high iron/high bone ash
level, 9-12% each. The tomato red colour reportedly comes
from microscopic iron (ferric or whatever) phosphate crystals.
Appears to prefer oxidation, up & down. Our tomato red
looks reddish-brown until about room temperature.
Some general (personal) observations on other high iron glazes:
The effect referred to as temmoku - rust/brown on highlights, black in depressions.
The entire glaze surface is rust/brown, the black is an overlay in depressions.
Increasing the iron content produces spangles, then metallic appearance.
Adding magnesium develops a plum red, increasing amounts
produces green crystals.
Increasing silica &/or potassium/sodium produces blacks.
Increasing alumina &/or calcium produces rust/browns.
Des
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
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