Eleanora Eden on wed 4 jan 06
Hi all you clay gurus:
I found this post from Jonathan Kaplan in the archives. He is
talking about making casting slips, but I am wondering if this also
applies to throwing bodies. EPK is the kaolin I have so its the one
I am using in my throwing body.
I made a list of all the kaolins listed on Insight and the analyses
are almost all identical, 1 alumina to 2 silica. So the differences
are somewhere else. (This feels like another area that with 2
degrees in ceramics I ought to know about, but I don't.)
Any explanations would be very helpful.
Eleanora
>
>Kaolins are the weakest link in a clay system. The strongest links are ball
>clays. WIth the proper selection of ball clays, your slip will have the
>lower viscosities that you need and cast faster and be much stronger. There
>are specific ball clays that are blended for casting. Don't assume that if
>you use OM 4, Tenn 5 or Tenn 10 in your plastic throwing body that they will
>be the best in your casting formula. They won't. The worst clays for casting
>bodies are EPK and OM 4. For the kaolin part, use Grolleg ($$$), or Tile 6
>and Kaopaque 20 together, or all with some combination with Pioneer Kaolin.
>Use Velvacast liberally. It is also a magic kaolin!! Stay away from EPK in
>your casting body.
>
>If the flint and spar are in a balanced relationship, then the spar will
>take up any free silica during vitrification and decrease the dunting
>potential. While this may be difficult to understand, you can replace about
>half the flint with Pyrax HS Pyrophyllite and keep the spar the same and get
>a very balanced body that is fully vitrified and will not craze your glazes.
>If you want some real proof, get a DTA on your clay body.
>
>Pyrophyllite is great juju in any ceramic body. We have used it for years in
>our plastic bodies for jiggering and RAM pressing, and it has been a
constant in all out casting formulae.
skiasonaranthropos@FSMAIL.NET on wed 4 jan 06
Hi Eleanora,
Without exception the best kaolin for a throwing body is Super Standard
Porcelain, also known as SSP. Its the strongest, whitest and most plastic
that youll find
Regards,
Antony
David Beumee on wed 4 jan 06
Hi Eleanora,
You've made a good choice using EPK, and for cost, plasticity, and whiteness, it is an excellent choice for a domestic(US) kaolin for use in a throwing body.
The most plastic domestic kaolin that I have tested is Helmer kaolin from Idaho, and is available in 325 mesh, but doesn't fire particularly white. Next to Helmer, Tile #6 kaolin has very good plasticity for a domestic kaolin used in a throwing body, but also fires to a very dark color (for a kaolin).
Super Standard Porcelain from England fires a light grey white in reduction at cone 10 and has a smooth and dense texture. The test bar exhibits very pronounced cracking, as do almost all kaolins when fired alone, with only fair plasticity in comparison to Helmer, EPK, Sapphire, Standard Porcelain, Dry Branch(Georgia kaolin),and poor plasticity in comparison to Helmer and Tile #6. I call Super Standard "Super Shrink", as it's 23% shrinkage at cone 10 in reduction is a full 3% higher shrinkage rate than any of the dozen kaolins I have tested. It is also extremely expensive for US potters to consider as a choice for their porcelain bodies. Hope this helps.
David Beumee
Lafayette, CO
www.davidbeumee.com
-------------- Original message ----------------------
From: Eleanora Eden
> Hi all you clay gurus:
>
> I found this post from Jonathan Kaplan in the archives. He is
> talking about making casting slips, but I am wondering if this also
> applies to throwing bodies. EPK is the kaolin I have so its the one
> I am using in my throwing body.
>
> I made a list of all the kaolins listed on Insight and the analyses
> are almost all identical, 1 alumina to 2 silica. So the differences
> are somewhere else. (This feels like another area that with 2
> degrees in ceramics I ought to know about, but I don't.)
>
> Any explanations would be very helpful.
>
> Eleanora
>
>
> >
> >Kaolins are the weakest link in a clay system. The strongest links are ball
> >clays. WIth the proper selection of ball clays, your slip will have the
> >lower viscosities that you need and cast faster and be much stronger. There
> >are specific ball clays that are blended for casting. Don't assume that if
> >you use OM 4, Tenn 5 or Tenn 10 in your plastic throwing body that they will
> >be the best in your casting formula. They won't. The worst clays for casting
> >bodies are EPK and OM 4. For the kaolin part, use Grolleg ($$$), or Tile 6
> >and Kaopaque 20 together, or all with some combination with Pioneer Kaolin.
> >Use Velvacast liberally. It is also a magic kaolin!! Stay away from EPK in
> >your casting body.
> >
> >If the flint and spar are in a balanced relationship, then the spar will
> >take up any free silica during vitrification and decrease the dunting
> >potential. While this may be difficult to understand, you can replace about
> >half the flint with Pyrax HS Pyrophyllite and keep the spar the same and get
> >a very balanced body that is fully vitrified and will not craze your glazes.
> >If you want some real proof, get a DTA on your clay body.
> >
> >Pyrophyllite is great juju in any ceramic body. We have used it for years in
> >our plastic bodies for jiggering and RAM pressing, and it has been a
> constant in all out casting formulae.
>
> ______________________________________________________________________________
> 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.
Michael Wendt on wed 4 jan 06
On Helmer:
Michael Ginn has some in his lab and has been successful in removing most of
the iron. Fired whiteness was substantially improved so if i-minerals
decides to add a processing line for Helmer, it might be available sans iron
along with Moose Creek Spar.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Ivor and Olive Lewis on fri 6 jan 06
Dear Eleanora Eden,
Choice of basic clay when designing a plastic body depends on your =
requirements.
If Plasticity is paramount, as it is for a body used when throwing, then =
choose clays that have a vary small particle size. This property is =
common in Ball Clay but not in Kaolin. Plastic Kaolins are uncommon so =
if you find one, treasure it !
If colour is important then look at the analysis for things which =
discolour clay. Iron oxides are the main culprits but Ilmenite also =
causes discolouration problems.
If translucency is a desired quality avoid clay that has a high Titanium =
dioxide content. This substance acts as an opacifier which is why Rutile =
is used to opacify glazes.
This may seem like an over simplification to some people but it is part =
of the quintessence of Clay Knowledge
Best regards,
Ivor Lewis.
Redhill,
South Australia.
skiasonaranthropos@FSMAIL.NET on fri 6 jan 06
Hello David,
Someone appears to have given you flawed information regarding Grolleg and
Standard Porcelain: having been around their production facilities I can
advise that no form of calcination is used. Perhaps the confusion may have
arisen due to a misunderstanding about the drying used. In common with
many industrial minerals, and kaolin production worldwide, processes to
reduce the moisture are used. However these will have been chosen so as
not to impair the clays properties. If you wish I can email you details of
the processes used
I was surprised with your comments regarding Super Standard Porcelain.
Whilst I agree that its whiteness is maximised in oxidising atmospheres Im
amazed that you consider it exhibits =93only fair plasticity=94 Having
assessed a huge number of kaolins from many different sources SSP is
unquestionably highly plastic for a china clay. And how can it be less
plastic than Standard Porcelain when by very definition it is =93Super=94
Standard Porcelain; the properties of strength, whiteness and plasticity
having been enhanced
Tile #6 and Sapphire are strong and plastic, although despite its name,
good marketing!, EPK is not exceptionally so. However if whiteness and
translucency are desired all three would be unattractive because of high
iron and titanium. Its also noted that it has been reported that deposits
for Tile#6 are running rather low
The relatively high shrinkage of Super Standard Porcelain you describe is
partly attributable to its higher particle size which does contribute to
some of its beneficial properties. The high montmorillionite content of
Tile #6 would also give high shrinkage
Regards,
Antony
David Beumee on fri 6 jan 06
Antony wrote:
" Someone appears to have given you flawed information regarding Grolleg and
> Standard Porcelain: having been around their production facilities I can
> advise that no form of calcination is used. Perhaps the confusion may have
> arisen due to a misunderstanding about the drying used. In common with
> many industrial minerals, and kaolin production worldwide, processes to
> reduce the moisture are used. However these will have been chosen so as
> not to impair the clays properties. If you wish I can email you details of
> the processes used"
Yes, please email me the details of Grolleg and Standard Porcelain processing. I have always heard that these clay deposits were washed from the cliffs, therefore a great deal of drying would be needed. I'm glad to find out that so much heat is not used so as to impair "plasticity". Now that I know from Craig's comments about the deposits being primary kaolins, I understand why these clays are so short.
"> I was surprised with your comments regarding Super Standard Porcelain.
> Whilst I agree that its whiteness is maximised in oxidising atmospheres Im
> amazed that you consider it exhibits "only fair plasticity" Having
> assessed a huge number of kaolins from many different sources SSP is
> unquestionably highly plastic for a china clay. And how can it be less
> plastic than Standard Porcelain when by very definition it is "Super"
> Standard Porcelain; the properties of strength, whiteness and plasticity
> having been enhanced."
All the kaolins I have tested are wet mixed and allowed to soak thouroughly to obtain maximum plasticity, then dried to moist consistency for testing, but all such tests are by definition subjective. For the testing that I have done myself in my own studio, according to my experience with using porcelain, Super Standard has a smooth and dense feel, but was not in my opinion as plastic feeling as Standard, Pioneer, Sapphire, Dry Branch, or EPK, and most definately not as plastic as Tile #6 or Helmer. Again Antony, these findings are by definition subjective!
Please tell me what you mean by enhanced properties of strength. Are we talking about workability or fired strength?
"> Tile #6 and Sapphire are strong and plastic, although despite its name,
> good marketing!, EPK is not exceptionally so. However if whiteness and
> translucency are desired all three would be unattractive because of high
> iron and titanium."
Again, please tell me of what you are refering when you you spaeak about strength.
You say that Tile#6, Sapphire, and EPK have high titanium and iron content. I keep hearing on Clayart how terribly important lack of titanium is to obtain translucency. No doubt you're all correct. Translucency has never been of high importance to me, but whiteness of a porcelain body most definately is. No kaolin I have tested compares in whiteness to New Zealand Ultrafine H. Next in line are Standard and Super Standard, according to my testing in reduction at cone 10. EPK, Macnamee, Grolleg, Sapphire and Dry Branch all test about the same whiteness, and Tile#6, Helmer, and Pioneer fire darkest. Hopefully Michael Wendt's comment means a brighter and lighter future for Helmer. This is good news! Helmer has very good plasticity for a kaolin, particularly if the rumor you've heard about the availability of Tile #6 is true.
"> The relatively high shrinkage of Super Standard Porcelain you describe is
> partly attributable to its higher particle size which does contribute to
> some of its beneficial properties. The high montmorillionite content of
> Tile #6 would also give high shrinkage.
"higher particle size?" You mean larger particle size?
Good! So there is a naturally ocurring bentonite in Tile 6, but the shrinkage rate of Super Standard is 5% more than Tile 6; 18% shrinkage for Tile #6 and 23% shrinkage for Super Standard.
David Beumee
www.davidbeumee.com
Lafayette, CO
-------------- Original message ----------------------
From: skiasonaranthropos@FSMAIL.NET
> Hello David,
> Someone appears to have given you flawed information regarding Grolleg and
> Standard Porcelain: having been around their production facilities I can
> advise that no form of calcination is used. Perhaps the confusion may have
> arisen due to a misunderstanding about the drying used. In common with
> many industrial minerals, and kaolin production worldwide, processes to
> reduce the moisture are used. However these will have been chosen so as
> not to impair the clays properties. If you wish I can email you details of
> the processes used
>
> I was surprised with your comments regarding Super Standard Porcelain.
> Whilst I agree that its whiteness is maximised in oxidising atmospheres Im
> amazed that you consider it exhibits "only fair plasticity" Having
> assessed a huge number of kaolins from many different sources SSP is
> unquestionably highly plastic for a china clay. And how can it be less
> plastic than Standard Porcelain when by very definition it is "Super"
> Standard Porcelain; the properties of strength, whiteness and plasticity
> having been enhanced
>
> Tile #6 and Sapphire are strong and plastic, although despite its name,
> good marketing!, EPK is not exceptionally so. However if whiteness and
> translucency are desired all three would be unattractive because of high
> iron and titanium. Its also noted that it has been reported that deposits
> for Tile#6 are running rather low
>
> The relatively high shrinkage of Super Standard Porcelain you describe is
> partly attributable to its higher particle size which does contribute to
> some of its beneficial properties. The high montmorillionite content of
> Tile #6 would also give high shrinkage
>
> Regards,
> Antony
>
> ______________________________________________________________________________
> 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.
David Beumee on fri 6 jan 06
Dear Michael,
This is excellent news! Please keep me informed if a lower iron Helmer becomes available. As to Helmer's good plasticity, any ideas? Might it have to do with processing? Example: I always thought that Imerys Grolleg and Standard Porcelain kaolins began as quite plastic kaolins, but because of heat processing to remove water content, the clays become somewhat calcined? Does anyone have any knowledge on this? Tile#6 kaolin has very good plasticity because of a naturally ocurring bentonite in the clay deposit, or so I hear. Is this why Helmer has good plasticity?
David Beumee
Porcelain by David Beumee
806 East Baseline Road
Lafayette, CO 80026
303-665-6925
www.davidbeumee.com
-------------- Original message ----------------------
From: Michael Wendt
> On Helmer:
> Michael Ginn has some in his lab and has been successful in removing most of
> the iron. Fired whiteness was substantially improved so if i-minerals
> decides to add a processing line for Helmer, it might be available sans iron
> along with Moose Creek Spar.
> Regards,
> Michael Wendt
> Wendt Pottery
> 2729 Clearwater Ave
> Lewiston, Idaho 83501
> USA
> wendtpot@lewiston.com
> www.wendtpottery.com
>
> ______________________________________________________________________________
> 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.
skiasonaranthropos@FSMAIL.NET on sat 7 jan 06
Hello David,
You correct that extraction of the English kaolins begins with them being
washed from cliffs. The subsequent processing is complex, and involves:
particle size classification, magnetic treatment, settling, dewatering in
filter presses as well as drying. However temperatures of the latter are
sufficiently low to effect the water only and not the clay. I understand
there are also patent processes used to increase the properties of the clay
=93 .. these findings are by definition subjective=94 Yes very much so ...
plasticity is difficult to assess; I would go as far to say impossible to
measure. Whilst not disagreeing with your on assessments I very strongly
disagree with the opinion that primary kaolins will be short. Yes some
will be and some will not ... but not by definition. The fact that English
kaolins are exported worldwide shows they are valued ... and this includes
consistency, whiteness, strength and plasticity
You asked =93 .. please tell me of what you are referring when you speak
about strength.=94 This is the unfired mechanical strength of clay, often
quoted as MOR or Modulus Of Rupture. Higher strengths will of course be
generally more attractive
The source of TiO2 in kaolins is not always the same; perhaps its within
the kaolinite lattice or from accessory minerals such as rutile. However
its presence reduces both translucency and whiteness
I certainly agree about the excellent optical properties of the Mew
Zealand china clays, though its worth noting this halloysite and not
kaolinite. Also they exhibit very low plasticity, and consequently are
often used in conjunction with a white, plastic kaolin such as Super
Standard
To answer about the enhanced properties of Super Standard Porcelain
against Standard Porcelain: SP is a very good kaolin being white, strong
with good plasticity, however SSP is even more so: both have negligible
TiO2. The mid range Fe2O3 for SP is 0.68% with SSP at 0.41%. The mid range
MOR for SP is 450 psi with SSP at 780 psi. Although some claim higher
strengths equate to higher plasticity this assumption is not universal.
However for similar groups of kaolins, in this case of English origin, its
valid.
As for the Helmer kaolin. The reported analysis of around 1.1% Fe2O3 and
1.2% TiO2 are very high in comparison to many kaolins, and consequently
would have a low fired whiteness. Although I can not comment about its
plasticity its chemical analysis suggests a relatively low overall clay
content. If the clay has a significant halloysite content, as I have
understand has been claimed, this may be helping the strength but may
impact negatively on plasticity, casting behaviour and by imparting high
shrinkage
By higher particle size I meant finer ... I should have made this more
clear
Hope that answers your questions. I will email of off list with some
information I have on the production of kaolin, though I hope you will
allow me a few days to locate
Antony
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