Antoinette on mon 27 dec 04
Use EPK. It is much cheaper than grolleg and works very well.
Antoinette Badenhorst
105 Westwood Circle
Saltillo, MS 38866
(662) 869-1651
www.clayandcanvas.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of clifton
wood
Sent: Monday, December 27, 2004 6:36 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: china clay - epk or grolleg?
Hi, everyone.
i'm getting ready to do a bunch of cone 6 glaze testing & have 2 village
idiot questions.
here's the first....
quite a few of the recipes call for china clay.
i checked the bookshelf, and know that china clay is a kaolin.
i have 2 clays i could use.... EPK or grolleg.
but i don't know why i would choose one over the other.
i checked out hamer & rhodes, but couldn't get an answer.
your expertise is appreciated!
clifton, norwich & sabra - www.claycat.com
________________________________________________________________________
______
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Paul Luminaux on mon 27 dec 04
I would suggest EPK... it is a purer clay... less fluxes, more pure supplier
of silica and alumina
>From: clifton wood
>Reply-To: Clayart
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: china clay - epk or grolleg?
>Date: Mon, 27 Dec 2004 19:36:16 -0500
>
>Hi, everyone.
>
>i'm getting ready to do a bunch of cone 6 glaze testing & have 2 village
>idiot questions.
>
>here's the first....
>
>quite a few of the recipes call for china clay.
>
>i checked the bookshelf, and know that china clay is a kaolin.
>
>i have 2 clays i could use.... EPK or grolleg.
>
>but i don't know why i would choose one over the other.
>
>i checked out hamer & rhodes, but couldn't get an answer.
>
>your expertise is appreciated!
>
>
>
>clifton, norwich & sabra - www.claycat.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.
_________________________________________________________________
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Dave Finkelnburg on mon 27 dec 04
Good question. The EPK is a Georgia kaolin with about 1% titanium dioxide and some iron. The Grolleg has almost no TiO2, and less iron. EPK is cheap, Grolleg expensive. Use EPK unless you are trying to make a glaze that is very sensitive to titania content, such as a blue celadon. You can test batches with one and the other and compare the results. For most glazes you won't be able to tell any difference.
Dave
clifton wood wrote:
Hi, everyone.
i'm getting ready to do a bunch of cone 6 glaze testing & have 2 village
idiot questions.
here's the first....
quite a few of the recipes call for china clay.
i checked the bookshelf, and know that china clay is a kaolin.
i have 2 clays i could use.... EPK or grolleg.
but i don't know why i would choose one over the other.
i checked out hamer & rhodes, but couldn't get an answer.
your expertise is appreciated!
clifton, norwich & sabra - www.claycat.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.
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clifton wood on mon 27 dec 04
Hi, everyone.
i'm getting ready to do a bunch of cone 6 glaze testing & have 2 village
idiot questions.
here's the first....
quite a few of the recipes call for china clay.
i checked the bookshelf, and know that china clay is a kaolin.
i have 2 clays i could use.... EPK or grolleg.
but i don't know why i would choose one over the other.
i checked out hamer & rhodes, but couldn't get an answer.
your expertise is appreciated!
clifton, norwich & sabra - www.claycat.com
Snail Scott on tue 28 dec 04
At 07:36 PM 12/27/2004 -0500, you wrote:
>i have 2 clays i could use.... EPK or grolleg.
>but i don't know why i would choose one over the other.
Grolleg is whiter, and more expensive in the US
(it's from Britain).
EPK is less white, and cheaper in the US (it's
from Florida).
Porcelain folks often prefer grolleg for its
whiteness, and the color response that is gets
from celadon glazes (it has less titanium than
EPK).
For glaze-making, I almost always to use EPK,
just because it's a handy all-purpose kaolin.
The special reasons for choosing grolleg just
don't matter to my work, so I've never bothered
to keep it in stock.
Most folks in the US use EPK for similar reasons.
The cost difference for glaze-making quantities
is not significant, but the extra whiteness and
low titanium content won't matter for most glazes.
Most US recipes are written for EPK or maybe
6-Tile kaolin, and often just call for 'kaolin',
but since your recipe calls it 'china clay' rather
than kaolin, it makes me think it was originally
a British recipe, and written that way out of
custom, not because it really mattered.
If you post the recipe, maybe some folks could
venture an opinion. It probably won't matter
much, though. If you've already got both, go
ahead and test both. If you've only got EPK (or
6-Tile) just use that. It'll be fine.
-Snail
Jon Pacini on tue 28 dec 04
Greetings All ---
For all intents and purposes EPK will be the common choice for kaolin in
glazes. At least here in North America. The kaolin is in the glaze primarily
to introduce Alumina and/or a bit of plasticity/adhesion. Just about any
kaolin will pretty much do that in a satisfactory manner.
Of course every kaolin brings a little something different to the party. EPK
will bring more titanium than the Grolleg will. If the Glaze is going to be
a transparent or translucent one and there is a large percentage of kaolin
in the formula, your choice of kaolin will impact the out come of your
glaze.
Ron could address this question in a more technical manner but that s your
basic seat of the pants answer.
By the way ----I ve been experimenting a bit with the New Zealand material
Ultra fine H. It s a Hallyosite, a type of volcanic kaolin. It seems to make
the clearest of clears. Its primary use is in very translucent commercial
Porcelains/Bone Chinas and it appears to bring that quality to glazes also.
If you re working with transparent glazes this would be a good material to
experiment with.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
Jon Pacini on wed 29 dec 04
Greetings All--Hi David---- I've NEVER been able to get anyone who is in
the KNOW to tell me what's in Southern Ice. Who can blame them.
I have done X ray diffractions of the body and the signature leads me to
believe that MAY be the type of mineral they are using. Also the Ultrafine H
does come from the same part of the world. A lot of conjecture and
circumstantial evidence.
We have 20 tons of the Ultrafine H in stock. It is available for purchase.
This material is whiter and lends more translucency to porcelain than any
other material I've ever seen. It makes Grolleg look gray.
Also--- I've developed a ^6 Porcelain using the Ultrafine-H, it's called
Frost. It is currently available here in California under the # S-3126. It
does look a lot like a Southern Ice type porcelain, very white, very
translucent.
However I'd like to note that Laguna's not really interested in competing
with Southern Ice. Laguna is after all the distributor for that material.
Plus we don't have the ability to blung and filter press our clays, which
Southern Ice is, so we can't really make the same thing anyway.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
Jon Pacini wrote:
By the way ----I ve been experimenting a bit with the New Zealand material
Ultra fine H. It s a Hallyosite, a type of volcanic kaolin. It seems to make
the clearest of clears. Its primary use is in very translucent commercial
Porcelains/Bone Chinas and it appears to bring that quality to glazes also.
If you re working with transparent glazes this would be a good material to
experiment with.
Do you know if Ultra Fine H is the kaolin used in Southern Ice, which has
such a different feel than Grolleg or EPK bodies? Is this Hallyosite kaolin
available in quantity for experimentation for porcelain bodies?
David Beumee
DavidBeumee.com
-------------- Original message ----------------------
From: Jon Pacini
> Greetings All ---
>
> For all intents and purposes EPK will be the common choice for kaolin in
> glazes. At least here in North America. The kaolin is in the glaze
primarily
> to introduce Alumina and/or a bit of plasticity/adhesion. Just about any
> kaolin will pretty much do that in a satisfactory manner.
>
> Of course every kaolin brings a little something different to the party.
EPK
> will bring more titanium than the Grolleg will. If the Glaze is going to
be
> a transparent or translucent one and there is a large percentage of kaolin
> in the formula, your choice of kaolin will impact the out come of your
> glaze.
>
> Ron could address this question in a more technical manner but that s your
> basic seat of the pants answer.
>
> By the way ----I ve been experimenting a bit with the New Zealand material
> Ultra fine H. It s a Hallyosite, a type of volcanic kaolin. It seems to
make
> the clearest of clears. Its primary use is in very translucent commercial
> Porcelains/Bone Chinas and it appears to bring that quality to glazes
also.
> If you re working with transparent glazes this would be a good material to
> experiment with.
>
> Best regards
> Jon Pacini
> Clay Manager
> Laguna Clay Co
>
>
____________________________________________________________________________
__
> 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 wed 29 dec 04
Jon Pacini wrote:
By the way ----I ve been experimenting a bit with the New Zealand material
Ultra fine H. It s a Hallyosite, a type of volcanic kaolin. It seems to make
the clearest of clears. Its primary use is in very translucent commercial
Porcelains/Bone Chinas and it appears to bring that quality to glazes also.
If you re working with transparent glazes this would be a good material to
experiment with.
Do you know if Ultra Fine H is the kaolin used in Southern Ice, which has such a different feel than Grolleg or EPK bodies? Is this Hallyosite kaolin available in quantity for experimentation for porcelain bodies?
David Beumee
DavidBeumee.com
-------------- Original message ----------------------
From: Jon Pacini
> Greetings All ---
>
> For all intents and purposes EPK will be the common choice for kaolin in
> glazes. At least here in North America. The kaolin is in the glaze primarily
> to introduce Alumina and/or a bit of plasticity/adhesion. Just about any
> kaolin will pretty much do that in a satisfactory manner.
>
> Of course every kaolin brings a little something different to the party. EPK
> will bring more titanium than the Grolleg will. If the Glaze is going to be
> a transparent or translucent one and there is a large percentage of kaolin
> in the formula, your choice of kaolin will impact the out come of your
> glaze.
>
> Ron could address this question in a more technical manner but that s your
> basic seat of the pants answer.
>
> By the way ----I ve been experimenting a bit with the New Zealand material
> Ultra fine H. It s a Hallyosite, a type of volcanic kaolin. It seems to make
> the clearest of clears. Its primary use is in very translucent commercial
> Porcelains/Bone Chinas and it appears to bring that quality to glazes also.
> If you re working with transparent glazes this would be a good material to
> experiment with.
>
> Best regards
> Jon Pacini
> Clay Manager
> Laguna Clay Co
>
> ______________________________________________________________________________
> 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 thu 30 dec 04
Jon Pacini wrote;
> We have 20 tons of the Ultrafine H in stock. It is available for purchase.
> This material is whiter and lends more translucency to porcelain than any
> other material I've ever seen. It makes Grolleg look gray.
Betcha a nickel it's what's used in Southern Ice, but there's no reason and no need to copy anyone's body, porcelain or otherwise. As you say, because Laguna doesn't blunge and filter press your bodies, there's no way Southern Ice could be duplicated. I know you want me to go through the supplier here in Denver to make orders, so I'll call them and ask to have 10 pounds sent. Can you give me prices for Ultrafine H?
David Beumee
davidbeumee.com
Lafayette, CO
-------------- Original message ----------------------
From: "Jon Pacini"
> Greetings All--Hi David---- I've NEVER been able to get anyone who is in
> the KNOW to tell me what's in Southern Ice. Who can blame them.
>
> I have done X ray diffractions of the body and the signature leads me to
> believe that MAY be the type of mineral they are using. Also the Ultrafine H
> does come from the same part of the world. A lot of conjecture and
> circumstantial evidence.
>
> We have 20 tons of the Ultrafine H in stock. It is available for purchase.
> This material is whiter and lends more translucency to porcelain than any
> other material I've ever seen. It makes Grolleg look gray.
>
> Also--- I've developed a ^6 Porcelain using the Ultrafine-H, it's called
> Frost. It is currently available here in California under the # S-3126. It
> does look a lot like a Southern Ice type porcelain, very white, very
> translucent.
>
> However I'd like to note that Laguna's not really interested in competing
> with Southern Ice. Laguna is after all the distributor for that material.
> Plus we don't have the ability to blung and filter press our clays, which
> Southern Ice is, so we can't really make the same thing anyway.
>
> Best regards
> Jon Pacini
> Clay Manager
> Laguna Clay Co.
>
>
> Jon Pacini wrote:
>
> By the way ----I ve been experimenting a bit with the New Zealand material
> Ultra fine H. It s a Hallyosite, a type of volcanic kaolin. It seems to make
> the clearest of clears. Its primary use is in very translucent commercial
> Porcelains/Bone Chinas and it appears to bring that quality to glazes also.
> If you re working with transparent glazes this would be a good material to
> experiment with.
>
> Do you know if Ultra Fine H is the kaolin used in Southern Ice, which has
> such a different feel than Grolleg or EPK bodies? Is this Hallyosite kaolin
> available in quantity for experimentation for porcelain bodies?
>
> David Beumee
> DavidBeumee.com
>
>
>
>
>
>
>
>
>
>
> -------------- Original message ----------------------
> From: Jon Pacini
> > Greetings All ---
> >
> > For all intents and purposes EPK will be the common choice for kaolin in
> > glazes. At least here in North America. The kaolin is in the glaze
> primarily
> > to introduce Alumina and/or a bit of plasticity/adhesion. Just about any
> > kaolin will pretty much do that in a satisfactory manner.
> >
> > Of course every kaolin brings a little something different to the party.
> EPK
> > will bring more titanium than the Grolleg will. If the Glaze is going to
> be
> > a transparent or translucent one and there is a large percentage of kaolin
> > in the formula, your choice of kaolin will impact the out come of your
> > glaze.
> >
> > Ron could address this question in a more technical manner but that s your
> > basic seat of the pants answer.
> >
> > By the way ----I ve been experimenting a bit with the New Zealand material
> > Ultra fine H. It s a Hallyosite, a type of volcanic kaolin. It seems to
> make
> > the clearest of clears. Its primary use is in very translucent commercial
> > Porcelains/Bone Chinas and it appears to bring that quality to glazes
> also.
> > If you re working with transparent glazes this would be a good material to
> > experiment with.
> >
> > Best regards
> > Jon Pacini
> > Clay Manager
> > Laguna Clay Co
> >
> >
> ____________________________________________________________________________
> __
> > 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 thu 30 dec 04
Actually - EPK is the whitest of the 4 kaolins we use and test at Tuckers -
Grolleg, tile 6, champion.
I had made the assumption that grolleg must be whiter as well but when you
look at the fired bars - EPK wins hands down in the whiteness category.
RR
>Grolleg is whiter, and more expensive in the US
>(it's from Britain).
>
>EPK is less white, and cheaper in the US (it's
>from Florida).
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
URL Krueger on fri 31 dec 04
On Thursday 30 December 2004 08:09 pm, Ron Roy wrote:
> I had made the assumption that grolleg must be whiter as
> well but when you look at the fired bars - EPK wins hands
> down in the whiteness category.
Could this be due to the higher amount of titanium in EPK?
After all, titanium dioxide is one of the whitest commonly
available substances known.
--
Earl K...
Bothell WA, USA
U.S. Marine Corp 1967-1971
Mr. Bush, Stop this war!
mailtoandrew@FSMAIL.NET on sat 1 jan 05
Hello Roy,
Were the tiles just kaolin, or incorporated into a body?
Also did you fire all to the same temperature / cone?
Thanks,
Andrew
mailtoandrew@FSMAIL.NET on sat 1 jan 05
Sorry Ron ... it was a mistake to address my last post by your surname.
Andrew
Ron Roy on sun 2 jan 05
Hi Andrew - Ron here,
Every batch of Kaolin thet arrives gettes sampled - nothing added and fired
to both cone 10 oxidation and reduction.
Bars ar 1" w by 1/2' h by 6" long - weighed & boiled for two hours right
after unstacking - cooled and weighed again to get % absorption.
RR
>Hello Roy,
>
>Were the tiles just kaolin, or incorporated into a body?
>Also did you fire all to the same temperature / cone?
>
>Thanks,
>
>Andrew
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on sun 2 jan 05
HI Earl,
EPK is also whiter than Tile 6 and Pioneer which have quite a bit more TiO2
reported.
I do not have a clue as to why it is whiter but the usual contaminant would
be iron.
I often wonder if clay companies stretch the truth to try and improve sales
- the amount of iron contamination in the analysis I use for EPK is 0.69 -
the grolleg says 0.52 - the tile 6 says 0.30 for instance.
Most results for the tested Kaolins are at cone 10 oxidation and reduction
- the most reliable Kaolin is EPK - every other kaolin Tuckers tests
(Pioneer, Grolleg, Tile 6) show sometimes quite different shrinkage and
absorbency from shipment to shipment and sometimes from skid to skid.
Every time I line the kaolin bars up it is always the EPK that is whitest.
If you had asked me - could it be the amount of rutile involved my answer
would have been the same - I have no insight into that except I assume the
rutile would be disassembled in an analysis - into iron and titanion
dioxide - is that true?
RR
>On Thursday 30 December 2004 08:09 pm, Ron Roy wrote:
>> I had made the assumption that grolleg must be whiter as
>> well but when you look at the fired bars - EPK wins hands
>> down in the whiteness category.
>
>Could this be due to the higher amount of titanium in EPK?
>After all, titanium dioxide is one of the whitest commonly
>available substances known.
>--
>Earl K...
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
mailtoandrew@FSMAIL.NET on sun 2 jan 05
Hello Ron,
Thanks for the further information following my questions.
I wonder if your assessment of EPK being whiter than Grolleg after firing
is actually comparing vitrification: there is a positive relationship
between water absorption and fired whiteness. As EPK is quite a bit more
refractory than Grolleg, typical K20 values of 0.33 and 1.85%
respectively, for a cone 10 firing the highest water absorption would be
expected for the former ... do your routine tests bear this out? .... and
consequently would look whiter.
A comparison at the same degree of vitrification would be interesting.
Regards,
Andrew
Ivor and Olive Lewis on mon 3 jan 05
Dear Ron Roy,
A Happy New Year to you.
I think the answer to your question <<...I have no insight into that
except I assume the rutile would be disassembled in an analysis - into
iron and titanium dioxide - is that true? >>
There two ways I would approach this question.
One would be to assume all of the iron and all of the titanium are
combined as a single mineral. The ratio of Titania to Fe203 or FeO
would distinguish Rutile from Ilmenite; FeO = TiO2 then Ilmenite:
FeO<<The second would be to do a mineral separation based on density. I
have found that if you use a Gold Pan on raw terra cotta and flush the
fines from the dish you are left with a selection of dark heavy
minerals. These are susceptible to the influence of a magnet and can
be segregated with that implement. Strongly magnetic fractions might
be magnetite; weakly magnetic, Ilmenite. But these are dark minerals.
Rutile may be contaminated with Iron but this is usually below 10% and
the mineral is white to light in colour. If you have enough to do a
density determination its SG is slightly lower than that of Ilmenite.
Perhaps using optical physics might be a better way to sort out this
problem. I say this because translucency improves as you eliminate
those components from a clay batch that have wide variance in
Refractive Index (RI), that is, they are much higher or lower than the
RI of Silica. (RI Quartz = 1.54 : RI Rutile = 2.6 ). Perhaps Rutile
improves whiteness by having a high reflectivity, hence the whiteness
under well illuminated conditions. So a high contamination of rutile
could indicate the potential of reducing the degree of translucency in
a fired porcelain.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ivor and Olive Lewis on mon 3 jan 05
Dear Ron Roy,
Given that you test kaolin as it is delivered, can you explain why
knowledge of adsorption is important in the fired raw material. What
does this tell you about the working properties of the material and do
you do the same with other raw materials such as ball clay?
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Edouard Bastarache Inc. on mon 3 jan 05
Ivor,
"FeO = TiO2"
This is a schematic view of this very variable chemical.
TiO2 may vary from 31-33% to »60% depending on where
it is mined. Here in Quebec we have the largest massive ilmenite
deposit, but very low in TiO2 (31-33%).
Ferric oxide (Fe2O3) is the dominant iron oxide in ilmenite,
black iron oxide is the other one and causes the black color
of the material.
Plus there may be many other oxides in the ore such as:
SiO2
Al2O3
CaO
MgO
Impurities
Later,
"Ils sont fous ces quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
Jon Pacini on mon 3 jan 05
Greetings All--------
Ron wrote I had made the assumption that grolleg must be whiter as well but
when you
look at the fired bars - EPK wins hands down in the whiteness category.
I should amend my previous statement that Grolleg is the whitest. EPK is
white, no doubt about it. Very white and here s the key -----very opaque. It
lends itself to very white bodies, but does not tend to lend itself well to
translucent ones. And that I believe was where David was going in his post.
Also it is not the most plastic of kaolins in spite of its name.
Don t get me wrong, you can certainly make a white translucent porcelain out
of EPK and it might even suit your personal preferences for throwing
characteristics.
However Grolleg tends to be a very good choice for translucent porcelains.
And there are a couple of reasons for this. The primary one is the
translucency that it imparts. And this can be attributed to it s vitreous
nature at ^10 and low TiO2. These factors coupled with the very small
percentage of iron account for the gray appearance of Grolleg. With Grolleg
you can use more clay and less spar/silica to achieve a translucent
porcelain. In using more clay you generally end up with a better throwing
body. EPK is still quite porous at ^10 in comparison to Grolleg and derives
much of it s whiteness from it s under fired nature and it s higher TiO2
content. It will therefore take more spar/silica to get EPK to be
translucent, and you end up with less clay in the body.
Whiteness and translucency is a subtle dance, and nearly always you
sacrifice one for the other.
It may be that one clay suits your throwing style better than the other, and
that has to be taken into consideration when developing a body. So again it
comes down to personal preferences as to which way you go. What
characteristics you want from a body, and if one material was the cure all,
we d all be throwing with a body made from that material.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
Ron Roy on tue 4 jan 05
Hi Andrew,
I am looking at two pages of test data - one for EPK and another for Grolleg.
The absorption at cone 10 ox for the EPK ranges from 7.1% to as high as 9.6
- just looking at the numbers I would say the average is 8.5
The Grolleg testing covers a much longer period (99 to 04) with the
absorbency ranging from 4.9 up to 7.4.
I agree that the lower the absorption the more likely colour will be seen -
how ever in this case the colour cannot be attributed solely to porosity
for a couple of reasons.
Both clays are clearly underfired enough to minimize any colour enhancement
due to vitrification.
The data from the other kaolins tends to confirm - the off white colour
cannot be solely due to the differences in fired too temperatures.
Perhaps you would like me to send you some EPK Andrew - you could fire each
to the same degree of absorption and compare the colour.
RR
>Thanks for the further information following my questions.
>
>I wonder if your assessment of EPK being whiter than Grolleg after firing
>is actually comparing vitrification: there is a positive relationship
>between water absorption and fired whiteness. As EPK is quite a bit more
>refractory than Grolleg, typical K20 values of 0.33 and 1.85%
>respectively, for a cone 10 firing the highest water absorption would be
>expected for the former ... do your routine tests bear this out? .... and
>consequently would look whiter.
>
>A comparison at the same degree of vitrification would be interesting.
>Andrew
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
David Beumee on tue 4 jan 05
Hi Ron,
It's really quite amazing all the testing of clays that Tucker's does through your guidance. Were it that all clay body manufacturers were as diligent.
It's very helpful to my research to find out that EPK represents the best consistency of the kaolins that are tested at Tucker's. In talking to the quality control manager at the EPK mine in Florida, I was also able to find out that at 40000 tons per year mined, there is capacity for 50 more years of reserve, so the rumors about EPK running out are false, at least for a generation or two. It's really heartening to me to know that America's whitest kaolin deposit is going to be available for awhile. My testing of all EPK bodies is going well and revealing some fine results.
David Beumee
davidbeumee.com
Lafayette, CO
-------------- Original message ----------------------
From: Ron Roy
> Hi Andrew,
>
> I am looking at two pages of test data - one for EPK and another for Grolleg.
>
> The absorption at cone 10 ox for the EPK ranges from 7.1% to as high as 9.6
> - just looking at the numbers I would say the average is 8.5
>
> The Grolleg testing covers a much longer period (99 to 04) with the
> absorbency ranging from 4.9 up to 7.4.
>
> I agree that the lower the absorption the more likely colour will be seen -
> how ever in this case the colour cannot be attributed solely to porosity
> for a couple of reasons.
>
> Both clays are clearly underfired enough to minimize any colour enhancement
> due to vitrification.
>
> The data from the other kaolins tends to confirm - the off white colour
> cannot be solely due to the differences in fired too temperatures.
>
> Perhaps you would like me to send you some EPK Andrew - you could fire each
> to the same degree of absorption and compare the colour.
>
> RR
>
>
> >Thanks for the further information following my questions.
> >
> >I wonder if your assessment of EPK being whiter than Grolleg after firing
> >is actually comparing vitrification: there is a positive relationship
> >between water absorption and fired whiteness. As EPK is quite a bit more
> >refractory than Grolleg, typical K20 values of 0.33 and 1.85%
> >respectively, for a cone 10 firing the highest water absorption would be
> >expected for the former ... do your routine tests bear this out? .... and
> >consequently would look whiter.
> >
> >A comparison at the same degree of vitrification would be interesting.
> >Andrew
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
> ______________________________________________________________________________
> 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 tue 4 jan 05
Hi Ivor,
All clays are tested as they arrive.
Working properties are not linked (in my mind) to absorption.
Knowing absorption of clays is useful when trying to maintain % absorption
in formulated bodies - and which clays are more reliable.
The fewer clays in a body the more useful this kind of information is - as
bodies which reley on one or two main clays are more susceptable to
drifting away from ideal absorption and shrinkage.
RR
>Dear Ron Roy,
>Given that you test kaolin as it is delivered, can you explain why
>knowledge of adsorption is important in the fired raw material. What
>does this tell you about the working properties of the material and do
>you do the same with other raw materials such as ball clay?
>Best regards,
>Ivor Lewis.
>Redhill,
>S. Australia.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
mailtoandrew@FSMAIL.NET on tue 4 jan 05
Hello Ron,
Thanks for the further information: I=92m surprised there wasn=92t a gretaer=
difference in water absorption between the two.
I'm certainly interested in testing the two kaolins at equivalent
vitrification; hope you do not mind if I contact you off the list to
discuss more detail.
Regards,
Andrew
Ivor and Olive Lewis on tue 4 jan 05
Dear Edouard,
I would not be a bit surprised if regular assays did not reveal
Chrome, Manganese, and traces of other transitional elements in
Ilmenite.
But has Ilmenite been identified as a constituent in the clays under
discussion?
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Jon Pacini on wed 5 jan 05
Greetings All-------Hi Ivor-----------you wrote," So we would expect a high
loading of fluxing elements in Grolleg clay.
Do you have a mineral assay from the manufacturers ? "
The ECC and EPK Data sheets I have compare like this:
Grolleg SiO2 49, Al2O3 36, FeO2 .75, TiO .02, CaO.06, MgO.30, Na2O .10, K2O
1.85
EPK SiO2 45.91, Al2O3 38.71, FeO2 .42, TiO .34, CaO .09, MgO .12, Na2O .04,
K2O .22
So, yes according to the data sheets the Grolleg is higher in alkaline
fluxes, also Silica and Iron, and lower in Alumina and Titanium. With the
exception of the Iron, all these qualities lend themselves to an easier
approach to translucency. Whiteness may indeed be another matter.
I also have the absorption numbers done in our QA kiln here at Laguna, for
^10 ox, EPK 5.6%, Grolleg .15%. Not a surprise to me, but these results may
be to others.
Test was conducted in the following manner:
200 grams dry kaolin was moistened to a plastic consistency and the amount
of water noted. This was pressed into a standardized "bar" mold we use for
QA purposes. Dried at 150*f over night, then once fired in our updraft gas
kiln in an eight hour ^10 Oxidation firing. Samples were fired side by side
accompanied by appropriate Orton #10 std. cones. The shape of the cones at
the end of firing were an inverted "U" shape with the tip just touching the
shelf. Upon removal from the kiln the samples were weighed on an Ohaus
digital scale. They were then boiled in a pressure cooker for 2 hours. When
removed, the surface was lightly dried of excess water and the samples
reweighed. The difference between the two weights was divided into the dry
weight to reveal the absorption percentage.
I hope I didn't leave anything out. :)
So there is something going on here that belies the published chemical
analysis. I've never put much stock in them personally. This isn't because
they don't reflect what was tested in their lab, I'm sure they were very
diligent with their tests. It's just that I've never felt the data sheets
reflect exactly what's in the bag that is shipped.
Ron's made the assertion that the absorption of any given material doesn't
make much difference within a clay body and that may be true to a certain
extent. But if you start with a kaolin that has .15% absorption and that
kaolin makes up a large percentage of the body, the composition of that body
would need to be considerably different than when using one that has 5.6%
absorption. If you wanted similar performing bodies that is.
I'd also like to note that neither of these absorption numbers comes very
close to the numbers Ron mentioned. In looking at the manufacturers data
sheets, those are indeed the numbers they list. This only reinforces my
contention that the data sheets rarely reflect what is actually happening
with the minerals we use, at least under our conditions.
And that's an important point, OUR conditions. All materials need to be
tested under the conditions they will be used. I hate to harp on this, but
if you don't know how materials react under the conditions you are firing
them to, then how will you ever know what to expect when you open the kiln.
Test, Test, Test.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
Edouard Bastarache Inc. on wed 5 jan 05
Hello Ivor,
"But has Ilmenite been identified as a constituent in the clays...
Ivor"
I have never heard of Ilmenite identified as such in any raw
ceramic material, not even in Ilmenite itseklf.
Later,
"Ils sont fous ces quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
Ivor and Olive Lewis on wed 5 jan 05
Dear Ron,
Thanks for your information.
Since heating causes sintering and de-hydroxylisation, some of the
essential qualities needed by potters are destroyed when clay samples
are fired. I think this validates your opinion.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Jon Pacini on thu 6 jan 05
Greetings All---Hi Ron-------I misread your statement about raw material
absorption and it s relationship to body absorption. I reread it this
morning when I was looking over the newest digest and don t know how I came
up with what I did----my apologies to you and the list.
Best regards
Jon Pacini
Clay Manager
Laguna Clay
Ron Roy on thu 6 jan 05
Jon,
Where did this idea come from? Of course the refractoriness of any material
in a clay body - or glaze or slip - will have an effect on the final
melting.
I have said that there is a good reason to have many materials in a clay
body - so that if some go up and others go down they tend to even out - yes
- have a lot of one kind of clay in a body - and it fluctuate it - you
lose.
Knowing the materials used it is how I keep Tuckers bodies to the level of
absorption advertised.
All bodies are monitored by testing at the cone they are recommended to be
fired at. If they drift too far up or down - they are reformulated.
Since I know the absorption of each raw clay used in all the bodies - I
simply make adjustments.
If the % absorption is too low - a clay or clays with higher absorption are
subbed in for clays with lower absorptions.
In the mean time - over the years - I have mostly eliminated the clays that
are unreliable - again because the raw clays are tested.
The end result is - I seldom have to reformulate clay bodies now.
I was saying to Frank Tucker a few weeks ago - have you noticed I have not
had to change a clay body for months now - he says - looks like you are out
of a job. I say OK but when you need me again I will want a raise.
I don't understand how any clay supplier can do the job right if they don't
do the testing - neither do I understand how anyone who mixes their own
clay thinks they can get away with it forever.
The materials we use change continually - if you don't pay attention you
will pay the price - sooner or later.
I continually check the analysis of raw materials against what I know about
the refractoriness of those materials - and use calculation based on the
analysis to check any reformulation - I have yet to find a problem with
that approach.
In fact - when faced with the job of replacing a clay in a body when it's
off the market - I am confident I can get it right the first time - because
I have done it several times now.
Saying that the analysis does not match the material in the bag is a major
factor all the time is nonsense - most of the time it works just fine -
knowing which materials are unreliable is an important part of any clay
makers job.
RR
>Ron's made the assertion that the absorption of any given material doesn't
>make much difference within a clay body and that may be true to a certain
>extent. But if you start with a kaolin that has .15% absorption and that
>kaolin makes up a large percentage of the body, the composition of that body
>would need to be considerably different than when using one that has 5.6%
>absorption. If you wanted similar performing bodies that is.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on thu 6 jan 05
Then, Edouard, it probably does not exist
> Hello Ivor,
> I have never heard of Ilmenite identified as such in any raw
> ceramic material, not even in Ilmenite itseklf.
Best regards
Ivor.
mailtoandrew@FSMAIL.NET on fri 7 jan 05
Hello all,
Just throwing in my thoughts on this interesting topic ...
Secondary kaolins rather than primary are likely to be high TiO2. Whilst
the commonest contributor will be anatase, brookite and rutile, all
polymorphs of TiO2, other titania bearing minerals have been identified,
including ilmenite, FeTiO3.
Examples from literature are:
Havell & McVay identified illmenite in clays from Alabama
(Am.Ceram.Soc.Bull.18.1939)
Searle and Grimshaw state =93Occasionally sphene (calcium titanite)
crystals, CaTiSiO5, and sometimes ilmenite, FeTi3, are present.=94 The
Chemistry and Physics of Clays and Other Ceramic Materials. Ernest Benn
Limited. 1959
I still wonder if the high TiO2 in EPK does increase its whiteness,
certainly due to the high RI it is detrimental to translucency. With raw
materials used in ceramics being predominantly rocks and minerals rather
than chemicals care has to be taken with the interpretation of analyses
listed as oxides. Whilst it may be easy to think these suggest a mixture
of discrete oxides it is actually just a convention to describe the
complex constituent minerals. The minerals that are most likely
contributing to the EPK s TiO2 are anatase, rutile and ilmenite. In their
natural, untreated form are anything but white, ranging from black to
brown to grey.
Regards,
Andrew
Jon Pacini on fri 7 jan 05
Greeting All---
-Ron Wrote---- Saying that the analysis does not match the material in the
bag is a major
factor all the time is nonsense
I have been reviewing my X ray tests that go back to the early '80's on
Grolleg and though there is some minor variation, I don't see anything that
would lead me to believe that the fusion that is exhibited with my test bars
is anything abnormal. And after all, the EPK that was tested right along
side it matches up with even Ron's stated data fairly well. Unfortunately I
don't have any of the physical test bars for Grolleg that go back to that
time, but as I recall, Grolleg has pretty much always looked and acted in
this manner.
I know Ron seems to think my lack of confidence in the data sheets is
nonsense, but the ECC data sheet says
absorption is 6.5 % at 1280*C and it's contraction (shrinkage) is 13%. I can
buy into the contraction number; it is consistent with my data. But if I
read this correctly, and I ve been known to get reading wrong, 1280*C is the
temperature ECC did the absorption testing at and that is ^9/10 on the Orton
chart depending on temperature rate employed. The published absorption is
not what is actually the case. It's not even close. So I m not convinced my
feelings regarding Data Sheets are nonsense.
Andrew mentioned he was going to do some testing and I'm very interested in
seeing what he comes up with in they way of absorption.
Maybe this phenomenon has to do with sample preparation methods or some
other facet of the ECC testing that I'm not aware of. I've outlined my
methods in a previous post.
If anyone has any thoughts on this, I'll be happy to entertain them.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
David Beumee on fri 7 jan 05
As a previous email showed, a straight across analysis of Grolleg and EPK shows less iron content in EPK than Grolleg, but because of the higher titania content of the EPK an all EPK body fires more grey than an all Grolleg body.
Like you say, minerals contributing to titania content include illmenite and rutile, both of which fire quite dark.
David Beumee
david@davidbeumee.com
Lafayette, CO
-------------- Original message ----------------------
From: mailtoandrew@FSMAIL.NET
> Hello all,
>
> Just throwing in my thoughts on this interesting topic ...
>
> Secondary kaolins rather than primary are likely to be high TiO2. Whilst
> the commonest contributor will be anatase, brookite and rutile, all
> polymorphs of TiO2, other titania bearing minerals have been identified,
> including ilmenite, FeTiO3.
>
> Examples from literature are:
> Havell & McVay identified illmenite in clays from Alabama
> (Am.Ceram.Soc.Bull.18.1939)
> Searle and Grimshaw state “Occasionally sphene (calcium titanite)
> crystals, CaTiSiO5, and sometimes ilmenite, FeTi3, are present.” The
> Chemistry and Physics of Clays and Other Ceramic Materials. Ernest Benn
> Limited. 1959
>
> I still wonder if the high TiO2 in EPK does increase its whiteness,
> certainly due to the high RI it is detrimental to translucency. With raw
> materials used in ceramics being predominantly rocks and minerals rather
> than chemicals care has to be taken with the interpretation of analyses
> listed as oxides. Whilst it may be easy to think these suggest a mixture
> of discrete oxides it is actually just a convention to describe the
> complex constituent minerals. The minerals that are most likely
> contributing to the EPK s TiO2 are anatase, rutile and ilmenite. In their
> natural, untreated form are anything but white, ranging from black to
> brown to grey.
>
> Regards,
>
> Andrew
>
> ______________________________________________________________________________
> 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 sun 9 jan 05
Hi Jon,
The grolleg data seems to fit in with my results just fine - along with the
data for the EPK - so why are you jumping to the conclusion that it's the
data sheet that is wrong?
I have never heard of anyone doing absorption tests in a pressure cooker by
the way.
I am still using the test recommended by Rhodes in Clay and Glazes - boil
for two hours - which is the equivalent of so many minutes in a steam
autoclave. This makes me think you are over cooking - but that does not
explain your results. What procedure does ECC use?
Always cool before weighing after boiling or you lose some water to
evaporation. Always weigh samples as soon as they come out of the kiln -
before they absorb moisture from the air, always boil right after dry
weighing before moisture from air gets in or wrap well to prevent.
Any variation in the procedure can affect results - and weather is a factor
- heat and humidity.
I have always used a 6"x1"x1/2 inch bar for testing clays - the thickness
allows more exact results - many use thin tiles which can magnify any
errors.
It seems to me Jon - that if you don't get the same results as the other
guys - the next step is to repeat your tests.
RR
Always do at least two bars to see if there is a difference between them -
which will indicate something went wrong - like a void in the clay.
>I know Ron seems to think my lack of confidence in the data sheets is
>nonsense, but the ECC data sheet says
>absorption is 6.5 % at 1280*C and it's contraction (shrinkage) is 13%. I can
>buy into the contraction number; it is consistent with my data. But if I
>read this correctly, and I ve been known to get reading wrong, 1280*C is the
>temperature ECC did the absorption testing at and that is ^9/10 on the Orton
>chart depending on temperature rate employed. The published absorption is
>not what is actually the case. It's not even close. So I m not convinced my
>feelings regarding Data Sheets are nonsense.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on mon 10 jan 05
Dear Ron Roy,
I an understand making shrinkage, CoE, and adsorption tests of
prepared clay bodies. But to do this with a raw clay seems
incongruous. Why is it necessary and what is it able to tell you in a
predictive way.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
mailtoandrew@FSMAIL.NET on mon 10 jan 05
Hello David, and of course everyone else,
David noted .... =93As a previous email showed, a straight across analysis
of Grolleg and EPK shows less iron content in EPK than Grolleg,=94
I=92m a little confused, as various values have been quoted for Fe2O3 for
both EPK and Grolleg:
EPK: Jon notes 0.42% with Ron saying 0.69% and the website of the Feldspar
Corporation quoting 0.79%
Grolleg: Jon notes 0.75% with Ron saying 0.52% and ECCs data sheet is at
0.75%.
Whilst single values are likely to be as typical found there is still
quite a range .... thoughts anyone?
Regards,
Andrew
Jon Pacini on mon 10 jan 05
Greetings All----- Hi Ron---
You wrote----"The grolleg data seems to fit in with my results just fine -
along with the
data for the EPK - so why are you jumping to the conclusion that it's the
data sheet that is wrong?
I have never heard of anyone doing absorption tests in a pressure cooker by
the way."
I'm hardly jumping to conclusions, I've been at this for 30 years and having
a lack of faith in data sheets has developed slowly but surely over that
period of time.
The reasons I use the pressure cooker is because of the volume of tests we
do. The samples are immersed in water within the device and it comes up to
boil quite rapidly. When I worked for Westwood we used to boil the tests in
an open pan, ala Rhodes, but now we need to test samples from 150 tons of
prepared clays every day and we had to pick up the pace a bit.
I've been pressure-cooking the samples for quite a few years now and
generally get very similar results as boiling, actually leaning towards
higher absorption numbers rather than less. I attribute this to the greater
penetration of water within the sample under pressure.
I have however repeated the test, boiling this time, with the same results,
again with other clays along with it to act as control.
The shrinkage and deformation are not out of the ordinary for the Grolleg
sample. Clays made from this run of Grolleg seem to act as normal also. I
normally don't do absorption on raw materials unless something else pops up
and brings my attention to it. So I don't really know if this batch is that
much different from normal absorption or not. It certainly doesn't appear so
from the QA results of the clays made with it.
Perhaps as you say the ECC tests are done in another manner. Though that
still wouldn't explain the difference between our data. I'm stumped.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
Ivor and Olive Lewis on tue 11 jan 05
Dear Andrew,
Some people may not understand that such variable values seem to
indicate a time lapse in reporting.
No doubt the Producers, as part of their quality control (ISO 9002 ??)
make weekly or daily checks on what is being processed and report the
analysis of each batch before it is processed.
All the minerals we extract from Mother Earth are variable in their
composition. Producers have ways of minimising this variability. They
work to statistical rules when selecting samples. Realising they
cannot eliminate residual mineral fractions they work to "Limits"
which bracket the ideal value.
It is important to me to know if, when iron is being reported as
Fe2O3, if that is the industrial convention used in the analysis of
ceramic raw materials.
It is important also to know if these values were derived from
Limonite, Magnetite, Haematite. Ilmenite, Siderite, Pyrite, Marcasite,
Biotite or some other mineral which contains the Element Iron.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ron Roy on tue 11 jan 05
Hi Ivor,
First of all - having test data over the years is valuable because you can
see which clays are the most reliable - a very handy thing to know if what
you want is predictability in clay bodies from batch to batch.
Colour variation is good to know.
Soluble salts or lack of is always interesting.
Colour variation that does not correspond with vitrification is always
interesting.
Warpage that does not seen to correlate to increased shrinkage is a bad sign.
In the end - you wind up with a picture of the materials you are using -
and it does help - especially the intuitive part of decision making. For
instance - when trying to get a white body - and having seen which kaolin
is whitest is pretty basic - but how would you know that without testing.
I simply could not do my job properly without the test data - and my job is
to see to it that the clay bodies are relatively consistent in absorbency
and shrinkage from batch to batch.
I also dilatometer raw clay samples - again interesting to know which ones
show the highest quartz and/or cristobalite - again important information
when formulating bodies to be fired at cone 9 or above.
I don't know if I have answered the question properly - if not I will do
better the 2nd time.
RR
>Dear Ron Roy,
>I an understand making shrinkage, CoE, and adsorption tests of
>prepared clay bodies. But to do this with a raw clay seems
>incongruous. Why is it necessary and what is it able to tell you in a
>predictive way.
>Best regards,
>Ivor Lewis.
>Redhill,
>S. Australia.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on tue 11 jan 05
Hello Andrew,
I wonder what a difference of 1/3 of 1% of iron would show in any clay - I
would think hardly noticeable!
I would think the differences in colour would at least be due to some other
factors.
If raw materials are not tested - then how are we to even be aware of these
differences?
Soluble salts have quite an effect on colour for instance - they migrate to
the surface and flux - changing the surface colour.
When clays are processed - are chemicals added, is local water adding
anything, are the analysis done on the clays as they come from the mine or
after processing. Is any iron added from the processing machinery - are
some clays cleared of iron by magnets - how often are the magnets cleaned.
Something as simple as - how long was the equipment idle before being used
to mine the clay may even be a factor.
My point is - testing over long periods will show inconsistencies and
improve the clay makers chances of finding more suitable clays.
RR
>David noted .... =93As a previous email showed, a straight across analysis
>of Grolleg and EPK shows less iron content in EPK than Grolleg,=94
>
>I=92m a little confused, as various values have been quoted for Fe2O3 for
>both EPK and Grolleg:
>
>EPK: Jon notes 0.42% with Ron saying 0.69% and the website of the Feldspar
>Corporation quoting 0.79%
>Grolleg: Jon notes 0.75% with Ron saying 0.52% and ECCs data sheet is at
>0.75%.
>
>Whilst single values are likely to be as typical found there is still
>quite a range .... thoughts anyone?
>
>
>Regards,
>
>Andrew
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Ivor and Olive Lewis on wed 12 jan 05
Dear Ron,
I get the picture.
Those two tests are just part of an overall and comprehensive quality
control process.
Were I in North America I know where I would shop for my clay.
Best regards,
Ivor
mailtoandrew@FSMAIL.NET on wed 12 jan 05
Hello Ron,
I fully agree there are a range of factors that influence fired colour but
for the bodies and kaolins I ve worked with a difference of 0.3% Fe2O3 is
huge! The effect can very readily be appreciated with the eye let alone
using more sophisticated assessments. For all white bodies I ve used the
highest Fe2O3 in the kaolins is less than 1%, and less than 0.5% where
whiteness is at a premium
I could not agree more with your comments =93If raw materials are not
tested - then how are we to even be aware of these differences?=94 ... =93My=
point is - testing over long periods will show inconsistencies and improve
the clay makers chances of finding more suitable clays.=94 I think it was
other contributors that asked why some of the testing was necessary.
And as you suggest processing machinery can cause iron contamination,
though this is likely to result in dark specks after firing rather than an
overall darkening. Magnet treatment can reduce the iron content but what
different types are available: extremely powerful equipment is used to
remove paramagnetic minerals that may be naturally present whilst lower
strength, and much cheaper, types are sufficient to guard against
contamination from rusty machinery.
Kind regards,
Andrew
mailtoandrew@FSMAIL.NET on wed 12 jan 05
Hello Ivor,
Of course a single quoted value for the Fe2O3 can not be taken to be
correct for every lump, from every bag across decades. However the range
of values mentioned in this thread seem too wide, 0.42% to 0.69% for one
kaolin and 0.52% to 0.75% for another. A data sheet for Grolleg I have
gives a range of 0.68 to 0.82%.
It may be worth commenting on the information given on such sheets ...
some will be a specification, as the Fe2O3 is on the above example, which
means that if tested in accordance with set procedures a value within the
given range will be found. Other data may be given as typical; these are
derived from averaging test results and exact values can not be guaranteed.
What is important is the testing, and perhaps this is why Jons results
differ so from those on the data sheet. Different test methods give
different results ... this is not to suggest either way would be wrong
just different, and correct for the individual method used.
It is certainly convention to quote the iron content of ceramic raw
materials as Fe2O3 rather than other forms, and it s very rare to see
individual iron bearing minerals noted. There are of course reasons for
this, not least as chemical analysis readily lends itself to QC checks ...
quick, relatively low cost equipment and lower expertise requirement
compared to mineralogical analysis. There are drawbacks, examples:
chemical analysis can not differentiate between quartz and cristobalite
although dilatometery can. Another is identifying clay mineral species,
mineralogical analysis is needed here except for say the kaolinite group
where microscopy would also be used.
And from your post ... =93It is important also to know if these values were
derived from Limonite, Magnetite, Haematite. Ilmenite, Siderite, Pyrite,
Marcasite, Biotite or some other mineral which contains the Element Iron.=94=
I would suspect the answer from an analyst if asked to quantify these may
well be a question ... in which orifice do you want the sample inserted?!
Whilst chemical analyses are readily available the use of mineralogical
information is extremely useful. Indeed using chemical analyses alone can
be very, very misleading ... take a bit of calcined alumina and mix with
quartz and some water. The same elements as clay, or at least pure
kaolinite, but try throwing with it!
Recently mentioned on ClayArt have been copies of Gerstley Borate. Whilst
I ve had limited experience of the material I would have thought using
information on the minerals rather than chemical data alone is more likely
to be successful ... if a copy of a rock is wanted than why not make it as
a rock, a mixture of minerals, rather than as say a frit which I ve seen
suggested? I understand the major components in GB are Colemanite,
Hectorite and Ulexite ...as an aside the latter is a little bit of a
natural oddity due to its ability to transmit light along its fibrous
structure, hence why it s sometimes known as TV stone. The GB discussions
remind me of some attempts to replicate China stone ... A number of
recipes have been suggested to match chemistry but the resultant blends do
not offer comparable performance; with mineralogical information as well a
very close match can be made.
Kind regards,
Andrew
Ivor and Olive Lewis on thu 13 jan 05
Dear Andrew,
To make that suggestion shows you have not considered that differing
minerals have differing chemistries, differing physical constants and
behave differently when exposed to heat. Then you invoke the idea of
preparing a substitution by mixing existing minerals. Why the seeming
contradiction ?
Best regards,
mailtoandrew@FSMAIL.NET on fri 14 jan 05
Hello Ivor,
I disagree with your statement =93To make that suggestion shows you have not=
considered that differing minerals have differing chemistries, differing
physical constants and behave differently when exposed to heat.=94 I noted,
maybe less than clearly, what is information it is practical to obtain,
and its use. I m sorry if my post appeared dichotomous as I was not
proposing the exclusive use of either chemical or mineralogical
information, indeed I meant quite the reverse.
The development of replacement materials requires information, and ideally
this would include chemical, mineralogical and performance data. However
this data must be relevant, representative and available.
For ceramic raw materials, and many other minerals, one of the most widely
used techniques to assess composition is XRF analysis: it offers fast
response, good repeatability and the facility to be automated. However it
is noted that it can not analyse the elements and should information of
these be required other techniques are needed.
Mineralogical information can be obtained from, amongst others, XRD
analysis, thermal analysis, optical and electron microscopy. Analysis time
for these is generally much longer than for XRF.
At most these chemical and mineralogical techniques analyse a few grams,
and sometimes, a few milligrams. With individual raw material producers
processing may be millions of tonnes testing all production clearly would
be impossible. Therefore sampling techniques and those analysis techniques
that are fast, and reliable, used. A quick analysis allows many samples to
be tested, and hence give some confidence the results are valid to the
production bulk.
The speed and accuracy of XRF analysis means it is very widely used, and
the chemical analyses seen on data sheets are very commonly derived from
such tests. Mineralogical techniques are less suited to routine testing,
not least due to the very slow analysis time; some, or all, may be
undertaken but at a considerably reduced frequency.
Additionally XRF analysis offers a higher level of precision than
mineralogical techniques. Although influenced by a range of factors ...
element / mineral examined, concentration and equipment sensitivity ...
something like 0.01% for XRF compared to 1% for XRD would be typical.
Other techniques may be needed to differentiate some minerals; for example
microscopical examination where very, very small amounts are studied, and
its use accurately, and repeatedly, quantify each would be unrealistic.
So it may be possible to identify limonite, magnetite, haematite.
ilmenite, siderite, pyrite, marcasite and biotite and others in a clay
sample. But the time required would be very considerable, and may require
a number of different techniques. And how relevant would those values
obtained from a few grams be for thousands of tonnes material extracted
the following day, week, year, decade?
Care has to be taken with interpretation of all results: each type such as
chemical analyses, may be seen as part of the book that describes a raw
material but it s not the whole story, and assuming it is can be very
misleading.
In summary?
Ceramic raw materials are generally rocks and minerals
Information on the mineralogy of these is obtainable, but with some
difficulty
Information on the chemistry of raw materials is relatively easily
obtainable
Selection of analysis type has to consider: what information would be a
useful and the timescale for it to be relevant
Hope that clarifies my last post,
Regards,
Andrew
Ivor and Olive Lewis on sat 15 jan 05
Dear Andrew,
I cannot disagree with what you write.
But, regardless of the quantities of material being questioned, there
are ways of sampling that give reasonable representations on a batch
to batch basis.
My argument is that representation of a substance exclusively in terms
of Molecular Oxides (R2O, R2O3, RO2) denies information to those who
have to solve some of the problems.
Fe2O3 was used as an example of how a material may be misunderstood as
a residual substance in a clay mineral. Each of the Iron bearing
minerals I mentioned will behave in a different way as it is heated.
One of those minerals may melt. Others will decompose. Some may
participate in solid state reactions. There are those that have
properties which are exploited to obtain a superior final product.
Representation only as Fe2O3 conceals that knowledge.
Perhaps there is no need for the general clay artist to know or even
bother about these things. But they should not be disregarded or
discounted.
As I said in another context, small percentage of R2O may represent a
much greater amount of a stoneware flux. (say Na2O-Al2O3-6SiO2). But
if the R2O fraction is concealed as a constituent in solid solution in
another mineral it may be inconsequential. Published assays of
commonly used clays, Kaolins and Ballclays, seem to suggest there are
several of these on the market. Knowing the mineral content would help
clarify the situation.
Enjoy your weekend.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
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