Sam Hoffman on thu 25 nov 04
Hank-
With all of the lithium in your shino, do you ever run into shivering
problems? The shinos I have used that have 0.25+ Li20, either from
spodumene or straight lithium, will flake off if the application is too
thick. This is particularly true if they are not fired hotter than
cone 9. I have done dot tests (firing a raw pile of material to cone
10) with Lithium, and it behaves differently than most other
materials-actually shattered the clay trivet that I was testing on. (I
assume upon cooling) Pretty dramatic!
I'm glad Ivor mentioned Pioneer Pottery. I was inspired to reread my
copy, what a great text! Just proves that technological advances are
great, but certainly not the deciding factor for making great pots!
Now its time to start rereading the Potter's Book...
-Sam
PS-I am looking forward to getting together with you one day to discuss
Oregon's wealth of native materials for the adventurous potter. This
Santiam slip I found is great!
S.L. Hoffman Pottery
Corvallis, Oregon
www.samhoffman.com
On Nov 25, 2004, at 6:48 PM, Hank Murrow wrote:
> On Nov 25, 2004, at 4:06 PM, Ivor and Olive Lewis wrote:
>>
>> Looking for information about the nature of the Glassy Phase this
>> morning I paused when leafing through Michaels Cardew's "Pioneer
>> Pottery" Iron Red and Yellow.
>> Most interesting reading, yet I cannot recall reading this on Clayart.
>> I thought use of one of the red clays to provide the Iron content and
>> the need to reduce or eliminate Alkali Earth materials most
>> interesting. Well worth reading.
>
> Dear Ivor;
>
> That is why most Shino recipes contain lots of Sodium and Lithium in
> the flux column. If you want that firecolor indian red, that is. Also
> high Al/Si ratios. Phosphorus is helpful also, as long as you don't
> bring in Calcium with it, which will kill the red color. Here is the
> dope for my standby Shino, which is really red on an irony body:
>
>
> 0.159 K2O 1.593 Al2O3 5.246 SiO2
> 0.534 Na2O 0.006 Fe2O3 0.023 TiO2
> 0.041 CaO 0.067 P2O5 0.000 MnO2
> 0.010 MgO 0.101 F
> 0.256 Li2O
>
> 1: 3.3 Al/Si Ratio!!
>
> Cheers mate, Hank
> www.murrow.biz/hank
>
> _______________________________________________________________________
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>
Hank Murrow on thu 25 nov 04
On Nov 25, 2004, at 4:06 PM, Ivor and Olive Lewis wrote:
>
> Looking for information about the nature of the Glassy Phase this
> morning I paused when leafing through Michaels Cardew's "Pioneer
> Pottery" Iron Red and Yellow.
> Most interesting reading, yet I cannot recall reading this on Clayart.
> I thought use of one of the red clays to provide the Iron content and
> the need to reduce or eliminate Alkali Earth materials most
> interesting. Well worth reading.
Dear Ivor;
That is why most Shino recipes contain lots of Sodium and Lithium in
the flux column. If you want that firecolor indian red, that is. Also
high Al/Si ratios. Phosphorus is helpful also, as long as you don't
bring in Calcium with it, which will kill the red color. Here is the
dope for my standby Shino, which is really red on an irony body:
0.159 K2O 1.593 Al2O3 5.246 SiO2
0.534 Na2O 0.006 Fe2O3 0.023 TiO2
0.041 CaO 0.067 P2O5 0.000 MnO2
0.010 MgO 0.101 F
0.256 Li2O
1: 3.3 Al/Si Ratio!!
Cheers mate, Hank
www.murrow.biz/hank
Paul Lewing on fri 26 nov 04
on 11/25/04 6:48 PM, Hank Murrow at hmurrow@EFN.ORG wrote:
> That is why most Shino recipes contain lots of Sodium and Lithium in
> the flux column. If you want that firecolor indian red, that is. Also
> high Al/Si ratios. Phosphorus is helpful also, as long as you don't
> bring in Calcium with it, which will kill the red color. Here is the
> dope for my standby Shino, which is really red on an irony body:
>
>
> 0.159 K2O 1.593 Al2O3 5.246 SiO2
> 0.534 Na2O 0.006 Fe2O3 0.023 TiO2
> 0.041 CaO 0.067 P2O5 0.000 MnO2
> 0.010 MgO 0.101 F
> 0.256 Li2O
>
> 1: 3.3 Al/Si Ratio!!
Hank, I agree that (in my experience with mid-range oxidation iron reds) the
Al:Si ratio needs to be very high, mostly because the amount of alumina
needs to be quite low. But 1:3.3 is a very LOW ratio. Most glazes that
melt to any kind of a usable surface and do not run are between 5.5 and 12.
Paul Lewing, Seattle
Ivor and Olive Lewis on fri 26 nov 04
Dear Hank,
Did you read the tract I mentioned?
Thanks for your information.
Best regards,
Ivor
Hank Murrow on fri 26 nov 04
On Nov 25, 2004, at 10:03 PM, Sam Hoffman wrote:
> With all of the lithium in your shino, do you ever run into shivering
> problems? The shinos I have used that have 0.25+ Li20, either from
> spodumene or straight lithium, will flake off if the application is too
> thick. This is particularly true if they are not fired hotter than
> cone 9. I have done dot tests (firing a raw pile of material to cone
> 10) with Lithium, and it behaves differently than most other
> materials-actually shattered the clay trivet that I was testing on. (I
> assume upon cooling) Pretty dramatic!
No, I have never had any shivering with this glaze. I use Low-melt
Spodumene from Tanco (and Georgies), and have never had those troubles
with it. I use this glaze only on my stoneware body.
> I'm glad Ivor mentioned Pioneer Pottery. I was inspired to
> reread my
> copy, what a great text! Just proves that technological advances are
> great, but certainly not the deciding factor for making great pots!
I was lucky enough to be at the U of Oregon in '67 when Michael came
through for an extended visit with David Stannard and his son (who was
Michael's godson). He was here lecturing and potting for six weeks, and
used the lectures to present and refine much of the material that later
became "Pioneer Pottery".
Cheers, Hank in Eugene
www.murrow.biz/hank
Ivor and Olive Lewis on fri 26 nov 04
These topics surface from time to time in our exchanges.
Looking for information about the nature of the Glassy Phase this =
morning I paused when leafing through Michaels Cardew's "Pioneer =
Pottery" Iron Red and Yellow.
Most interesting reading, yet I cannot recall reading this on Clayart.
I thought use of one of the red clays to provide the Iron content and =
the need to reduce or eliminate Alkali Earth materials most interesting. =
Well worth reading.
About the Glassy Phase in Clay Bodies and Glazes! Though I accept the =
Zachariasen model for the Glass Phase in pure silica there is something =
amiss with the model when it is used to show the presence of modifying =
atoms in Lawrence and West (Fig 1-5, p 10).
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Hank Murrow on sat 27 nov 04
On Nov 26, 2004, at 7:43 PM, Paul Lewing wrote:
>>
> Hank, I agree that (in my experience with mid-range oxidation iron
> reds) the
> Al:Si ratio needs to be very high, mostly because the amount of alumina
> needs to be quite low. But 1:3.3 is a very LOW ratio. Most glazes
> that
> melt to any kind of a usable surface and do not run are between 5.5
> and 12.
> Paul Lewing, Seattle
Dear Paul;
I was referring to the very high amount of Al when I characterized my
recipe. See pics of this glaze at.....
http://www.murrow.biz/hank/shino-pots.htm
Cheers,
Hank in Eugene
www.murrow.biz/hank
Bruce Girrell on mon 29 nov 04
> > I thought use of one of the red clays to provide the Iron content and
> > the need to reduce or eliminate Alkali Earth materials most
> > interesting.
I found the following analysis for Redart in the archives (posted by David
Hendley):
Ca0 .03
Mg0 .26
K20 .25
Na20 .04
Ti02 .09
Fe203 .29
Al203 1.00
Si02 7.11
and this analysis on the Matrix website:
CaO 0.025
MgO 0.239
K20 0.268
Na2O 0.040
TiO2 0.083
Fe2O3 0.274
Al2O3 1.000
SiO2 6.647
P2O5 0.007
They seem reasonably close to one another and the dreaded calcium oxide
seems as though it might be low enough.
So how does one make use of the analysis information in order to determine
percentage of Redart to add to a recipe to achieve 4% iron content? And is
the calcium low enough or do I just get another brown glaze?
Thanks, Ivor, for the Pioneer Pottery reference.
Bruce Girrell
in northern Michigan, staving off the onset of winter,
not having access to any of Cardew's Nigerian clay and
obviously never having used this type of analysis info before
Michael Wendt on tue 30 nov 04
Bruce asked a question about Redart and gave this analysis from the Matrix
website:
CaO 0.025
MgO 0.239
K20 0.268
Na2O 0.040
TiO2 0.083
Fe2O3 0.274
Al2O3 1.000
SiO2 6.647
P2O5 0.007
To change the alumina unity to silica ratio to analysis percentages,
add up the listed values ( these came to 8.583 ). Divide 8.583 into 100 to
get 11.651. Multiply each value listed by 11.651 to get the percent value.
Here, Fe2O3 = 0.274 x 11.651 = 3.19 percent.
No matter how much Redart you add to a glaze, you will not reach 4% Iron.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Bruce wrote:
They seem reasonably close to one another and the dreaded calcium oxide
seems as though it might be low enough.
So how does one make use of the analysis information in order to determine
percentage of Redart to add to a recipe to achieve 4% iron content? And is
the calcium low enough or do I just get another brown glaze?
Thanks, Ivor, for the Pioneer Pottery reference.
Bruce Girrell
Ivor and Olive Lewis on tue 30 nov 04
Dear Bruce,
An interesting question. I will have to think about that!
Could be one for the real Glaze Guru's to answer.
Time to get out the Slide Rule.
Best regards,
Ivor.
daniel on wed 1 dec 04
Hi Bruce,
These do not look like anaylses. They look like alumina unity molecular
formulae. Looking at the digitalfire site they have redart at about 7.05%
Fe2O3. RR's MDT in Insight has it at 7.1%.
>
> I found the following analysis for Redart in the archives (posted by David
> Hendley):
> Ca0 .03
> Mg0 .26
> K20 .25
> Na20 .04
> Ti02 .09
> Fe203 .29
> Al203 1.00
> Si02 7.11
>
Assuming I'm correct on this, conversion to an analysis requires
multiplying each molar quantity by its molecular weight. The add all up and
do as Michael suggested. I have
For the first one I get :
CaO 0.2711
K2O 3.7943
MgO 1.6890
Na2O 0.3994
Ti02 1.1586
Fe2O3 7.4618
SiO2 68.8014
Al2O3 16.4243
This agrees pretty well with those sources I mentioned above.
> So how does one make use of the analysis information in order to determine
> percentage of Redart to add to a recipe to achieve 4% iron content? And is
> the calcium low enough or do I just get another brown glaze?
If I was doing this I'd be using glaze calc. s/w and sub it in in place of
other clay in the recipe and balance up the other numbers, so that nothing
gets too out of whack. The problem I think may arise is that you'll need
over 50% clay in the recipe if RedArt is your only source of iron. Sounds
like a recipe for crawling. If you would like I could take a look at subbing
this if you can send me the recipe you're working with.
Thanx
D
Belmont, California, USA
(ex terra australis)
Ron Roy on wed 1 dec 04
Hi Bruce,
The analysis I use for Red Art is:
SiO2 - 64.27
Al2O3 - 16.41
Fe2O3 - 7.04
TiO2 - 1.06
CaO - 0.23
MgO - 1.55
K2O - 4.07
Na2O - 0.10
LOI - 4.92
Total - 99.65
What you copied below is not an analysis - all analysis should total 100
but many we get do not include everything.
Below is a molecular formula with the unity on alumina - and no LOI info.
If I calculate the analysis I use to the mol formula with unity on alumina
I get.
Ca0 .03
Mg0 .24
K20 .27
Na20 .01
Ti02 .08
Fe203 .27
Al203 1.00
Si02 6.66
I'm not surprised to see that kind of difference - Red Art is variable and
will present problems with certain clays and glazes.
The Licorice glaze the group has reported on does vary - and some of the
different results may be due to the variability of Red Art at 65%.
By the way I can work out the analysis for any material if I have a
molecular formula - anyone can if they have calculation software that gives
analysis and molecular formulas - you just have to guess at the LOI.
There is probably a current analysis for Red Art on the Resco site - or
just fax em.
RR
>> > I thought use of one of the red clays to provide the Iron content and
>> > the need to reduce or eliminate Alkali Earth materials most
>> > interesting.
>
>I found the following analysis for Redart in the archives (posted by David
>Hendley):
>Ca0 .03
>Mg0 .26
>K20 .25
>Na20 .04
>Ti02 .09
>Fe203 .29
>Al203 1.00
>Si02 7.11
>
>and this analysis on the Matrix website:
>CaO 0.025
>MgO 0.239
>K20 0.268
>Na2O 0.040
>TiO2 0.083
>Fe2O3 0.274
>Al2O3 1.000
>SiO2 6.647
>P2O5 0.007
>
>They seem reasonably close to one another and the dreaded calcium oxide
>seems as though it might be low enough.
>
>So how does one make use of the analysis information in order to determine
>percentage of Redart to add to a recipe to achieve 4% iron content? And is
>the calcium low enough or do I just get another brown glaze?
>
>Thanks, Ivor, for the Pioneer Pottery reference.
>
>Bruce Girrell
>in northern Michigan, staving off the onset of winter,
>not having access to any of Cardew's Nigerian clay and
>obviously never having used this type of analysis info before
>
>______________________________________________________________________________
>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
daniel on thu 2 dec 04
Hi Ron,
Thanx for this. I had forgotten about LOI.
> Below is a molecular formula with the unity on alumina - and no LOI info.
Bruce, the reason my method got close was because Redart has only about 5%
LOI.
The method I put forward can only really be used if you know the LOI
composition, its percentage (which to some extent implies you have an
analysis), or there is no LOI.
Hope I did not cause more confusion rather than less.
Thanx
D
Belmont, California, USA
(ex terra australis)
Bruce Girrell on thu 2 dec 04
Thanks to all who have responded on this.
For those who may be following this thread but don't have access to Cardew's
book, Cardew's analysis of his Nigerian AB clay is
SiO2 55.46
Al2O3 21.34
Fe2O3 7.77
MgO 1.66
CaO 0.91
Na2O 0.76
K2O 2.87
TiO2 0.95
LOI 8.37
Ron Roy's analysis for Red Art (copied below my sig) shows that Red Art has
a higher Si/Al ratio but similar iron and better CaO compared to the AB
clay. MgO, which Cardew notes as being troublesome, is also similar to the
AB clay. Na and K are a little off, but I would think that those numbers
would be swamped by the neph sy and potash feldspar in the glaze formula.
Cardew, citing Parmelee, gives the (unity) formula for a iron red glaze as
K2O 0.8 Al2O3 1.17 SiO2 5.35
Na2O 0.2 Fe2O3 0.05
and provides a glaze recipe that he says comes close to meeting that:
North Cape neph sy 44%
Potash feldspar 34%
AB clay 20%
Kaolin 2%
My take on all of this is that, given a little toying around with the
fluxes, Red Art seems to be a suitable candidate as an iron source. I have a
glaze mixing session (for our normal glazes) in my near future. Seems like a
good time to throw in a nice little iron red experiment. I'll let you know
what I find out. If anyone cares to make any suggestions, I'd be happy to
consider them.
Bruce "line blendin' fool" Girrell
Ron Roy's analysis for Red Art:
SiO2 - 64.27
Al2O3 - 16.41
Fe2O3 - 7.04
TiO2 - 1.06
CaO - 0.23
MgO - 1.55
K2O - 4.07
Na2O - 0.10
LOI - 4.92
Total - 99.65
Ron Roy on sat 4 dec 04
Hi Bruce,
Just an additional note on this - one of the problems I have found with
materials like low fire red clays - as a source of iron - you tend to get a
muddier colour.
It is also a problem using them to source iron in high fired bodies -
because the CaO and MgO will facilitate cristobalite production.
I'm sure the other impurities that come along with those low fire clays
have a role in both problems as well.
I hope you will share the results of your experiments with us - if you need
help just let me know - it would be useful to do some control experiments
using less contaminated materials - just to see how the final colours are
affected.
RR
>
>My take on all of this is that, given a little toying around with the
>fluxes, Red Art seems to be a suitable candidate as an iron source. I have a
>glaze mixing session (for our normal glazes) in my near future. Seems like a
>good time to throw in a nice little iron red experiment. I'll let you know
>what I find out. If anyone cares to make any suggestions, I'd be happy to
>consider them.
>
>Bruce "line blendin' fool" Girrell
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Bruce Girrell on sat 4 dec 04
> one of the problems I have found with
> materials like low fire red clays - as a source of iron -
>you tend to get a muddier colour.
>it would be useful to do some control experiments
>using less contaminated materials
Thanks, Ron
What started this was Ivor's citation of Cardew, who feels that it is
important to use a ferruginous clay as the iron source for best color. Time
will tell, I guess.
Bruce
Ron Roy on sun 5 dec 04
Hi Bruce,
I did not mean to imply that all iron bearing clays will give muddy colours
by the way - firing them up will give the clues about which are better. I
do know that elevated alumina will help give brighter colours with iron.
Finding the right iron bearing clays will pay off in the long run - and
paying attention to contaminants present in other materials.
This is the kind of project that will pay off big time - for many potters.
RR
>> one of the problems I have found with
>> materials like low fire red clays - as a source of iron -
>>you tend to get a muddier colour.
>
>>it would be useful to do some control experiments
>>using less contaminated materials
>
>Thanks, Ron
>
>What started this was Ivor's citation of Cardew, who feels that it is
>important to use a ferruginous clay as the iron source for best color. Time
>will tell, I guess.
>
>Bruce
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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