Bruce Girrell on sat 11 dec 04
Ron Roy suggested that, in experimenting with the Cardew recommendation for
an iron red glaze, it would wise to include a version using RIO as a
control. I set about attempting to come up with a matching version using RIO
and now have a question as to what makes for the best match. So Ron, if
you're tuned in, I'd appreciate your comments. Others who have experience in
this area are, of course, welcome as well.
Parmelee's basic formula, Cardew's starting point, is
K2O 0.8 Al2O3 1.17 SiO2 5.35 Si:Al 4.57
Na2O 0.2 Fe2O3 0.05
Cardew provides a recipe:
North Cape neph sy 44
Potash feldspar 34
AB clay 20
Kaolin 2
and provides a unity formula of
K2O 0.54 Al2O3 1.16 SiO2 5.36 Si:Al 4.62
Na2O 0.34 Fe2O3 0.05
MgO 0.10
Being a little short on the supply of North Cape neph sy and AB clay I
substituted raw materials that I do have:
Red Art glaze
Spectrum A270 neph sy 44
Custer feldspar 34
Red Art 20
EPK 2
Using Insight and the Ron Roy MDT:
K2O 0.39 Al2O3 1.16 SiO2 6.27 Si:Al 5.41
Na2O 0.51 Fe2O3 0.06
MgO 0.05
CaO 0.05
LOI 1.69 COE 8.09
Well, the Na and K have reversed and the Si:Al ratio has jumped quite a bit.
Not the best match, but I took it as a starting place. Neglecting Parmelee
and Cardew temporarily, I set about trying to match this recipe with another
in which I replaced the Red Art with RIO. My first attempt added a suitable
amount of RIO and held EPK the same:
Glaze I
Neph sy 45.25
Custer 52.0
EPK 2.0
RIO 1.75
K2O 0.42 Al2O3 1.07 SiO2 5.81 Si:Al 5.41
Na2O 0.53 Fe2O3 0.06
MgO 0.01
CaO 0.05
LOI 0.76 COE 8.56
The fluxes are high relative to the Si and Al. This seems reasonable, as I
removed all the Red Art. Adding in more EPK, though, trashes the Si:Al
ratio. In round 2 I tried to add EPK while holding everything as close to my
first recipe as possible:
Glaze II
Neph sy 40.0
Custer 55.0
EPK 3.5
RIO 1.5
K2O 0.44 Al2O3 1.11 SiO2 5.99 Si:Al 5.41
Na2O 0.51 Fe2O3 0.06
MgO 0.01
CaO 0.05
LOI 0.96 COE 8.46
Things go the right direction, but I didn't get much more clay in there.
Reasoning that the ratio of Na:K was less important than the total Si and Al
(and that Na and K were reversed from Cardew anyway), I tried:
Glaze III
Neph sy 32.5
Custer 60.0
EPK 6.0
RIO 1.5
K2O 0.47 Al2O3 1.16 SiO2 6.29 Si:Al 5.41
Na2O 0.48 Fe2O3 0.06
MgO 0.01
CaO 0.04
LOI 1.29 COE 8.32
Now, some questions:
1) Was this a logical progression? Nelecting an attempt to match
Cardew/Parmelee and simply trying to match the RIO version with the Red Art
version, how would you have gone about it?
2) Between Glaze II and Glaze III, which do you feel would be closer in
character to the Red Art glaze?
3) What further adjustments would you suggest to make the RIO control batch
as close as possible to the Red Art version?
Next I wanted to see what I could do to get the recipes as close to the
Cardew recipe as possible. For the Red Art version I came up with:
Neph sy 76.0
Custer 2.0
Red Art 18.5
EPK 3.5
K2O 0.25 Al2O3 1.17 SiO2 5.40 Si:Al 4.63
Na2O 0.64 Fe2O3 0.05
MgO 0.05
CaO 0.06
LOI 1.96 COE 8.41
and for the RIO version:
Neph sy 10.25
Custer 64.0
EPK 25.0
RIO 0.75
K2O 0.58 Al2O3 1.73 SiO2 8.04 Si:Al 4.63
Na2O 0.37 Fe2O3 0.05
MgO 0.01
CaO 0.04
LOI 3.93 COE 7.55
And the questions:
1) In the Red Art version, most everything is in line but the Na:K ratio is
way off. How much difference does this make? I see the COE has jumped.
2) In the RIO version Na:K and Si:Al are right, but the total Si and Al are
high. What effect does that have?
3) Which of these two glazes would you expect to be more similar to the
Cardew recipe?
4) Out of all of this, how do I choose the best starting point (base glaze
upon which I would make variations) to compare to Cardew/Parmelee?
I know this has been really long. I appreciate you taking the time to wade
through it.
Bruce Girrell
Bruce Girrell on mon 13 dec 04
> Instead of answering each question I just did it
Thank you. I wasn't looking for someone to do my homework, though. I was
trying to work through the problem and asked for help when I couldn't go any
further. In the first set of recipes I was attempting to balance out two
recipes where one subbed in a small amount of RIO and removed a large amount
of Red Art. So the problem in the first part was how to make those two as
close to one another accounting for the radical change in clay content, but
totally disregarding the end goal of getting close to the Parmelee formula.
My primary question for the first portion of the exercise was basically
"Given the recipe that immediately follows 'Being a little short on the
supply of North Cape neph sy and AB clay' as a starting point, does Glaze
III represent a reasonable approximation when RIO is used in place of Red
Art?" In other words, am I going about this in a reasonable manner? I'm more
interested in method than the actual numbers in this case.
In the second part of the exercise, I attempted to make two different glazes
more closely approximating Cardew's unity formula, one using Red Art to
supply the iron and the other using RIO for the iron. This part is more
about the numbers, but the methodology is still an important thing that I'm
trying to understand.
In the RIO version, I thought I did an OK job of getting most things to
match with the exception of the Si and Al being high. The ratio is right,
but the total quantities are high. What effect would you expect that to
have? To put it another way, when I am trying to adjust glazes, do I need to
pay more attention to the Si:Al ratio or to the quantities (or do both count
equally)?
In your version I don't understand why you added the MgCO3. The glazes are
purposefully short on CaO, as Cardew notes that even small amounts of
calcium will turn the color muddy. He feels that Mg is trouble as well. What
property were you acting on with the addition of the Mg? Shouldn't the Na
and K provide adequate fluxing action by themselves?
I hadn't thought about adding alumina hydrate directly and was balancing the
silica with EPK, which has a pretty low Si:Al ratio of its own (while
getting a little clay back in there), but that was getting me into trouble
with the Si and Al quantities. What motivated you to use both OM4 and
bentonite?
Thanks for your help. I hope the weather is being nicer to you now.
Bruce "Ivor, this is all _your_ fault" Girrell
Ron Roy on mon 13 dec 04
Hi Bruce,
Instead of answering each question I just did it - keeping in mind the
following.
Red Art brings too much silica - and so does spar - so I concentrated on
Neph Sy which is low in silica.
Getting the alumina up calls for some alumina hydrate - if you use kaolin
or ball clay you get too much silica again.
The Cardew formula has no CaO but because we must use the Neph Sy we have
to take some - and I also used Mag Carb because there is no silica.
This should be a matt glaze by the way because the ratio is below 5 but -
it is going to be a shino type - and - may also craze - and will if you add
soda ash.
I don't have the experience to tell how much the reversed amounts of Sodium
and potassium will affect it.
Red Art brings some impurities with it so I would recommend doing this
without the Red Art - just do it over with red iron and adjust the
materials till you get the same or close formula - you will see the
difference.
Neph Sy - 67.5 (you may have to counter the defloccing with Epsom)
Custer - 8.0
Mag Carb - 0.7
Red Art - 20.0
Alumina Hydrate - 2.3
OM#4 - 1.5
Bentonite - 2.0
Total 102.0
The problem with the Parmelee formulation is - there are no raw materials
that will give that ratio of KNaO with the low silica and no other fluxes -
that I know of.
Here is a recipe that matches it except for the small amount of CaO and the
opposite ratio of KNaO.
Neph Sy - 74.0
Custer - 16.0
OM#4 - 10.0
Red Iron - 1.5
Bentonite 2.0
Total 103.5
If this leads to more questions just fire away - if you do some testing I
want to know the results please - make a couple of tiles for me.
Snow here - power went off and I lost most of this already tonight so I'm
stopping now.
RR
>Ron Roy suggested that, in experimenting with the Cardew recommendation for
>an iron red glaze, it would wise to include a version using RIO as a
>control. I set about attempting to come up with a matching version using RIO
>and now have a question as to what makes for the best match. So Ron, if
>you're tuned in, I'd appreciate your comments. Others who have experience in
>this area are, of course, welcome as well.
>
>Parmelee's basic formula, Cardew's starting point, is
>K2O 0.8 Al2O3 1.17 SiO2 5.35 Si:Al 4.57
>Na2O 0.2 Fe2O3 0.05
>
>Cardew provides a recipe:
>North Cape neph sy 44
>Potash feldspar 34
>AB clay 20
>Kaolin 2
>
>and provides a unity formula of
>K2O 0.54 Al2O3 1.16 SiO2 5.36 Si:Al 4.62
>Na2O 0.34 Fe2O3 0.05
>MgO 0.10
>
>Being a little short on the supply of North Cape neph sy and AB clay I
>substituted raw materials that I do have:
>
>Red Art glaze
>Spectrum A270 neph sy 44
>Custer feldspar 34
>Red Art 20
>EPK 2
>
>Using Insight and the Ron Roy MDT:
>K2O 0.39 Al2O3 1.16 SiO2 6.27 Si:Al 5.41
>Na2O 0.51 Fe2O3 0.06
>MgO 0.05
>CaO 0.05
>
>LOI 1.69 COE 8.09
>
>Well, the Na and K have reversed and the Si:Al ratio has jumped quite a bit.
>Not the best match, but I took it as a starting place. Neglecting Parmelee
>and Cardew temporarily, I set about trying to match this recipe with another
>in which I replaced the Red Art with RIO. My first attempt added a suitable
>amount of RIO and held EPK the same:
>
>Glaze I
>Neph sy 45.25
>Custer 52.0
>EPK 2.0
>RIO 1.75
>
>K2O 0.42 Al2O3 1.07 SiO2 5.81 Si:Al 5.41
>Na2O 0.53 Fe2O3 0.06
>MgO 0.01
>CaO 0.05
>
>LOI 0.76 COE 8.56
>
>The fluxes are high relative to the Si and Al. This seems reasonable, as I
>removed all the Red Art. Adding in more EPK, though, trashes the Si:Al
>ratio. In round 2 I tried to add EPK while holding everything as close to my
>first recipe as possible:
>
>Glaze II
>Neph sy 40.0
>Custer 55.0
>EPK 3.5
>RIO 1.5
>
>K2O 0.44 Al2O3 1.11 SiO2 5.99 Si:Al 5.41
>Na2O 0.51 Fe2O3 0.06
>MgO 0.01
>CaO 0.05
>
>LOI 0.96 COE 8.46
>
>Things go the right direction, but I didn't get much more clay in there.
>Reasoning that the ratio of Na:K was less important than the total Si and Al
>(and that Na and K were reversed from Cardew anyway), I tried:
>
>Glaze III
>Neph sy 32.5
>Custer 60.0
>EPK 6.0
>RIO 1.5
>
>K2O 0.47 Al2O3 1.16 SiO2 6.29 Si:Al 5.41
>Na2O 0.48 Fe2O3 0.06
>MgO 0.01
>CaO 0.04
>
>LOI 1.29 COE 8.32
>
>Now, some questions:
>1) Was this a logical progression? Nelecting an attempt to match
>Cardew/Parmelee and simply trying to match the RIO version with the Red Art
>version, how would you have gone about it?
>2) Between Glaze II and Glaze III, which do you feel would be closer in
>character to the Red Art glaze?
>3) What further adjustments would you suggest to make the RIO control batch
>as close as possible to the Red Art version?
>
>Next I wanted to see what I could do to get the recipes as close to the
>Cardew recipe as possible. For the Red Art version I came up with:
>
>Neph sy 76.0
>Custer 2.0
>Red Art 18.5
>EPK 3.5
>
>K2O 0.25 Al2O3 1.17 SiO2 5.40 Si:Al 4.63
>Na2O 0.64 Fe2O3 0.05
>MgO 0.05
>CaO 0.06
>
>LOI 1.96 COE 8.41
>
>and for the RIO version:
>
>Neph sy 10.25
>Custer 64.0
>EPK 25.0
>RIO 0.75
>
>K2O 0.58 Al2O3 1.73 SiO2 8.04 Si:Al 4.63
>Na2O 0.37 Fe2O3 0.05
>MgO 0.01
>CaO 0.04
>
>LOI 3.93 COE 7.55
>
>And the questions:
>1) In the Red Art version, most everything is in line but the Na:K ratio is
>way off. How much difference does this make? I see the COE has jumped.
>2) In the RIO version Na:K and Si:Al are right, but the total Si and Al are
>high. What effect does that have?
>3) Which of these two glazes would you expect to be more similar to the
>Cardew recipe?
>4) Out of all of this, how do I choose the best starting point (base glaze
>upon which I would make variations) to compare to Cardew/Parmelee?
>
>I know this has been really long. I appreciate you taking the time to wade
>through it.
>
>Bruce Girrell
>
>______________________________________________________________________________
>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
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on wed 15 dec 04
Hi Bruce,
I'll answer each in turn.
>My primary question for the first portion of the exercise was basically
>"Given the recipe that immediately follows 'Being a little short on the
>supply of North Cape neph sy and AB clay' as a starting point, does Glaze
>III represent a reasonable approximation when RIO is used in place of Red
>Art?" In other words, am I going about this in a reasonable manner? I'm more
>interested in method than the actual numbers in this case.
In your attempt to replace the red art with iron - first check the %
analysis to see if the Fe2O3 is about the same in your red iron version -
then note that the alumina and silica is short - add a combination of EPK,
silica and alumina hydrate till the Al2O3 and SiO2 mols are about the same
- and make sure the ratio is close. When the KNaO ratio is not the same you
cannot expect the expansion to be the same.
>In the second part of the exercise, I attempted to make two different glazes
>more closely approximating Cardew's unity formula, one using Red Art to
>supply the iron and the other using RIO for the iron. This part is more
>about the numbers, but the methodology is still an important thing that I'm
>trying to understand.
>
>In the RIO version, I thought I did an OK job of getting most things to
>match with the exception of the Si and Al being high. The ratio is right,
>but the total quantities are high. What effect would you expect that to
>have? To put it another way, when I am trying to adjust glazes, do I need to
>pay more attention to the Si:Al ratio or to the quantities (or do both count
>equally)?
If your Al/Si mols are higher you are making the glaze more refractory - so
get em close. The Al/Si ration is important if you want the surface to be
the same - in this case - a shino type glaze - you want the ratio below 5 -
so iron will cone out of solution as the glaze cools.
>
>In your version I don't understand why you added the MgCO3. The glazes are
>purposefully short on CaO, as Cardew notes that even small amounts of
>calcium will turn the color muddy. He feels that Mg is trouble as well. What
>property were you acting on with the addition of the Mg? Shouldn't the Na
>and K provide adequate fluxing action by themselves?
I agree - avoid CaO and MgO for the "best" shinos - Stick with KNaO and
Li2O as much as possible. Knowing your materials is crucial when you are
doing such demanding glazes - Neph Sy is an ideal material for Shino type
glazes - high alkalies and low SiO2 but - there is some CaO and MgO.
When I did the first revision I was reacting to your 1st example - when you
use Red Art you get a significant amount of MgO.
>
>I hadn't thought about adding alumina hydrate directly and was balancing the
>silica with EPK, which has a pretty low Si:Al ratio of its own (while
>getting a little clay back in there), but that was getting me into trouble
>with the Si and Al quantities. What motivated you to use both OM4 and
>bentonite?
Neph Sy defloccs glazes and keeping them from settling becomes a problem -
Ball Clays work well with bentonite to help keep glazes suspended (I would
have used Bell Dark for my glaze) - EPK does not work as well as a
suspender - and - because ball clay has less Al2O3 - you can use more of it
- and ball clay works better than a kaolin with bentonite to help
suspension. My "rule" is always use ball clay if the added iron is not a
problem - and it rarely is - and it can cure crawling due to it's tougher
surface when dried. MOR (modulus of rupture) is an important factor when
choosing clays for glazes. One of the cures for a powdery dry clay is to
sub in ball clay for the kaolin for instance.
Red Art is not a true clay by the way - LOI is only around 5% - so looking
for ways to help it becomes important.
I'm sure there will be more questions Bruce - no problem. Understand how I
got to my numbers - it was just easier for me to do an example - in the end
it's not what you come up with - it's how you got there that is important
at this stage.
If you have a fax machine I can send you my analysis sheets for the most
common materials - or send me your address and I will mail them.
RR
>
>Thanks for your help. I hope the weather is being nicer to you now.
>
>Bruce "Ivor, this is all _your_ fault" Girrell
>
>______________________________________________________________________________
>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
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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