David Beumee on tue 15 oct 02
Jonathan,
Thanks for the Dover recipe you gave to Zac. I mixed a large enough batch to send you some if you
like. It has good plasticity, 15% shrinkage at cone 11, 1.37% absorption at cone 11, no warping or cracking in the fired bar, a
smooth and creamy texture and a mottled grey-white fired color in reduction. I can send the test bar if you want. The body fit
GTS 3-10, excellent glaze fit.
I'd like to read your upcoming article if you'd send me a copy.
Hope your time with Ian was rewarding to everyone. Linda Dadisman of Mile Hi sure is fired up.
I've done a study of stoneware talc bodies that I'd like your input on, if your're interested.
David Beumee
10/15/02 6:30:17 AM, Ceramic Design Group wrote:
>I think it is primarily a mental exercise to find out the COE of a
>particular clay body, or for that matter "grading" a clay body. I certainly
>do applaud any potter going to this great length to make sure everthing is
>"just right." My experience is that in ceramics, not everything may be "just
>right." Ceramics is a field that is filled with many variables. We all know
>to well how many and what they are! I do applaud the inquiry and hope that
>such an investigation produces the desired results you wish.
>
>The results you may get from this are only relevant to the particular batch
>of prepared body that you are currently using. The next batch may have
>similar working properties, may have relatively the same shrinkage and
>absorption, but I am certainly willing to bet that the COE will be
>different. Its important to understand that while the stuff in the bag or
>the box may look right, chances are that if you have some testing run on
>each and every batch of materials that you purchase and receive, they will
>exhibit a different COE. And even with even the most exhaustive testing
>procedures, it still does not take into account the biggest variable, which
>is firing procedure. Clay bodies that are supposed to have a firing range of
>cone 6-10 for example, are going to exhibit different numbers at each of
>these temperatures and how they are fired will dramatically effect the fired
>results. Any dillatometer test at each of the temperatures in the cone 6-10
>range will visually show this.
>
>Even the most obsessive "Type A" potter might find this a bit too trying.
>While this has some value in learning about how a clay body functions, I
>don't think that any of us has the time or the energy to devote to this
>every time a new batch of clay is prepared or you receive clay in the box. I
>would also posit that a majority of moist clay producers have the time and
>energy or care about it at all. And this is a fundamental problem. and
>certainly a huge issue for many.
>
>However, while some moist clay suppliers try to approach target numbers and
>can adjust, to some degree, for this, I would posit that more valuable data
>is obtained from a dillatometer test. This is where I would certainly put my
>trust and faith. You can certainly also have COE tests performed. Ron
>mentioned to me the other day in a phone call that using a dillatometer to
>create the necessary testing for a DTA, it is possible to use a formula
>coupled with these charts to determine the COE. At his NCECA presentation a
>few years ago, he showed how he lines up a test form a glaze sample and
>overlays that onto a test for a clay body. This is valuable and pertinent
>information. One would wish that the methodology he so tirelessly works with
>for a few companies and the diligence to which he helps people on this list
>would be one that ALL moist clay body manufacturers would embrace. It would
>certainly put at ease many on the list who need this data or have
>experienced some difficulty with their raw materials or clay in the box.
>
>My line line of thinking that in blending clay bodies, buy large lots of
>component materials with the same batch/date code. Use materials that are
>used by industry..... most kaolins, some red clays, some ball clays, flint,
>spar, pyrophyllite, etc., and stay away from materials that have been know
>to exhibit severe changes over time such as "fireclays" and some red clays.
>Certain "stoneware" clays might fall into this category also. Diversity
>particle sizes as well as choice of materials. It is also important to
>educate oneself.
>
>Over my many, many years of making my own clay, I have not noticed any
>problems that are directly attributed to COE's that are far out of what
>might be established as an acceptable range. If the bodies are compounded
>correctly they should perform well. I have calculated and mixed many bodies
>from cone 06-10 for our own use and for others: white bodies, red bodies,
>buff bodies, whitewares, stonewares and porcelains, casting formulae and
>plastic bodies, and my experience is that if you do a little bit of reading,
>testing, and have the desire to understand how it all works, then there is
>really little need to work with the COE of the clay body. Please understand
>that this is my opinion and only my opinion and is the result of what works
>for me. If a problem does develop, it is certainly easier for me to adjust
>a batch of glaze then to try to adjust some tons of mixed clay, be it clay
>in the box or your own blend. It is incumbent on a potter to be educated on
>running even the most simple of tests.....a shrinkage bar and test, an
>absorption bar and test, then test how that small sample of a proposed clay
>body takes your glazes under your own firing conditions. Put a glaze on it
>and do a freeze/ thaw test, test for stability of the glaze. And once these
>tests are done, then send a sample to a lab or to Ron for a DTA test. Any
>potter not willing to try and be educated and gain knowledge and ultimately
>assume a greater degree of control over their clay bodies and glazes is
>really just asking for trouble and is quite irresponsible, IMHO. And the
>same is true for those companies that produce moist clay in the box and
>don't take the time to insure that such blends do meet certain criteria.
>Enough said.
>
>In the next issue of Production Pottery Practices (supplement to Ceramic
>Industry) I will have an article on clays and clay bodies for the potter if
>you wish further information.
>
>Respectfully,
>
>Jonathan
>
>
>Jonathan Kaplan, president
>Ceramic Design Group
>PO Box 775112
>Steamboat Springs CO 80477
>voice and fax 970 879-9139
>info@ceramicdesigngroup.net
>
>Plant Location:
>1280 13th Street Unit 13
>Steamboat Springs CO 80487
>(please use this address for all deliveries via UPS, comman carrier, Fed Ex,
>etc.)
>
>"Custom design and manufacturing for the ceramic arts, giftware and pottery
>industries. Molds, models, and tooling for slip casting, jiggering and
>hydraulic pressing. Consultation on clay and glaze formulation, production
>systems,firing, and kilns.
>
>______________________________________________________________________________
>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.
>
Ceramic Design Group on tue 15 oct 02
I think it is primarily a mental exercise to find out the COE of a
particular clay body, or for that matter "grading" a clay body. I certainly
do applaud any potter going to this great length to make sure everthing is
"just right." My experience is that in ceramics, not everything may be "just
right." Ceramics is a field that is filled with many variables. We all know
to well how many and what they are! I do applaud the inquiry and hope that
such an investigation produces the desired results you wish.
The results you may get from this are only relevant to the particular batch
of prepared body that you are currently using. The next batch may have
similar working properties, may have relatively the same shrinkage and
absorption, but I am certainly willing to bet that the COE will be
different. Its important to understand that while the stuff in the bag or
the box may look right, chances are that if you have some testing run on
each and every batch of materials that you purchase and receive, they will
exhibit a different COE. And even with even the most exhaustive testing
procedures, it still does not take into account the biggest variable, which
is firing procedure. Clay bodies that are supposed to have a firing range of
cone 6-10 for example, are going to exhibit different numbers at each of
these temperatures and how they are fired will dramatically effect the fired
results. Any dillatometer test at each of the temperatures in the cone 6-10
range will visually show this.
Even the most obsessive "Type A" potter might find this a bit too trying.
While this has some value in learning about how a clay body functions, I
don't think that any of us has the time or the energy to devote to this
every time a new batch of clay is prepared or you receive clay in the box. I
would also posit that a majority of moist clay producers have the time and
energy or care about it at all. And this is a fundamental problem. and
certainly a huge issue for many.
However, while some moist clay suppliers try to approach target numbers and
can adjust, to some degree, for this, I would posit that more valuable data
is obtained from a dillatometer test. This is where I would certainly put my
trust and faith. You can certainly also have COE tests performed. Ron
mentioned to me the other day in a phone call that using a dillatometer to
create the necessary testing for a DTA, it is possible to use a formula
coupled with these charts to determine the COE. At his NCECA presentation a
few years ago, he showed how he lines up a test form a glaze sample and
overlays that onto a test for a clay body. This is valuable and pertinent
information. One would wish that the methodology he so tirelessly works with
for a few companies and the diligence to which he helps people on this list
would be one that ALL moist clay body manufacturers would embrace. It would
certainly put at ease many on the list who need this data or have
experienced some difficulty with their raw materials or clay in the box.
My line line of thinking that in blending clay bodies, buy large lots of
component materials with the same batch/date code. Use materials that are
used by industry..... most kaolins, some red clays, some ball clays, flint,
spar, pyrophyllite, etc., and stay away from materials that have been know
to exhibit severe changes over time such as "fireclays" and some red clays.
Certain "stoneware" clays might fall into this category also. Diversity
particle sizes as well as choice of materials. It is also important to
educate oneself.
Over my many, many years of making my own clay, I have not noticed any
problems that are directly attributed to COE's that are far out of what
might be established as an acceptable range. If the bodies are compounded
correctly they should perform well. I have calculated and mixed many bodies
from cone 06-10 for our own use and for others: white bodies, red bodies,
buff bodies, whitewares, stonewares and porcelains, casting formulae and
plastic bodies, and my experience is that if you do a little bit of reading,
testing, and have the desire to understand how it all works, then there is
really little need to work with the COE of the clay body. Please understand
that this is my opinion and only my opinion and is the result of what works
for me. If a problem does develop, it is certainly easier for me to adjust
a batch of glaze then to try to adjust some tons of mixed clay, be it clay
in the box or your own blend. It is incumbent on a potter to be educated on
running even the most simple of tests.....a shrinkage bar and test, an
absorption bar and test, then test how that small sample of a proposed clay
body takes your glazes under your own firing conditions. Put a glaze on it
and do a freeze/ thaw test, test for stability of the glaze. And once these
tests are done, then send a sample to a lab or to Ron for a DTA test. Any
potter not willing to try and be educated and gain knowledge and ultimately
assume a greater degree of control over their clay bodies and glazes is
really just asking for trouble and is quite irresponsible, IMHO. And the
same is true for those companies that produce moist clay in the box and
don't take the time to insure that such blends do meet certain criteria.
Enough said.
In the next issue of Production Pottery Practices (supplement to Ceramic
Industry) I will have an article on clays and clay bodies for the potter if
you wish further information.
Respectfully,
Jonathan
Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
info@ceramicdesigngroup.net
Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, comman carrier, Fed Ex,
etc.)
"Custom design and manufacturing for the ceramic arts, giftware and pottery
industries. Molds, models, and tooling for slip casting, jiggering and
hydraulic pressing. Consultation on clay and glaze formulation, production
systems,firing, and kilns.
Cat Yassin on tue 15 oct 02
In a message dated 10/15/2002 9:54:28 AM Central Daylight Time,
info@CERAMICDESIGNGROUP.NET writes:
> Put a glaze on it
> and do a freeze/ thaw test, test for stability of the glaze. And once these
> tests are done, then send a sample to a lab or to Ron for a DTA test. Any
> potter not willing to try and be educated and gain knowledge and ultimately
> assume a greater degree of control over their clay bodies and glazes is
> really just asking for trouble and is quite irresponsible, IMHO.
Jonathon, thanks for all this information! Aha, this is what Clayarts all
about! Its one thing to have book knowledge and another to have actual
experience. But to have both! Eventually I'll get there... Thanks again!
-Cat
S. Texas
Ron Roy on fri 18 oct 02
Just a few comments on Jonathan's comments.
I explained to Jonathan over the phone - I have dilatometer charts on
several clays over many years now - I am continually impressed by how
similar each are (the same body) over many years - perhaps amazed is a
better word.
Mind you I "adjust" each clay when needed to maintain shrinkage and
absorbency at levels advertised. And I do tend to substitute ingredients
which have a consistent track record based on testing.
This includes some fire clays by the way.
I also have a rule - at least 4 clays per body and never over 30% of any
one clay - and if the clay is over 20% make sure it's a clay that is not up
and down more than a little.
The other fact I feel I should comment on is the degree of miss fit
inherent in most potters clays and glazes. Potters tend to choose their
clays and glazes based on how they look - without any investigation into
how they fit with each other. The cracking tea pot or casserole are good
examples of what I am taking about.
Of all the problems I contend with from day to day - the fit problems are
the most frequent - and generally the easiest to deal with.
I can't count the times I have analysed a potters glazes - made adjustments
- and did not have to do anything else - the glazes looked the same and
stopped having fit problems. I am usually able to improve durability at the
same time.
There is a class of glazes that continually are difficult or impossible to
deal with - unbalanced (over fluxed mostly) glazes - many with only 3 or 4
materials in them.
In the end I am amazed that as much ware holds together as well as it does
- this does not mean we should not try to make it better in my mind - why
not - if we can avoid the consequences of that day when clay and glaze
conspire to necessitate a trip to the dump.
The testing is not that complicated and it does not take a lot of time -
I'm beginning to think most potters just don't want to do it so they make
it into something complicate and time consuming - it is not. The results
are interesting and wonderful for your peace of mind.
RR
>The results you may get from this are only relevant to the particular batch
>of prepared body that you are currently using. The next batch may have
>similar working properties, may have relatively the same shrinkage and
>absorption, but I am certainly willing to bet that the COE will be
>different. Its important to understand that while the stuff in the bag or
>the box may look right, chances are that if you have some testing run on
>each and every batch of materials that you purchase and receive, they will
>exhibit a different COE. And even with even the most exhaustive testing
>procedures, it still does not take into account the biggest variable, which
>is firing procedure. Clay bodies that are supposed to have a firing range of
>cone 6-10 for example, are going to exhibit different numbers at each of
>these temperatures and how they are fired will dramatically effect the fired
>results. Any dillatometer test at each of the temperatures in the cone 6-10
>range will visually show this.
>My line line of thinking that in blending clay bodies, buy large lots of
>component materials with the same batch/date code. Use materials that are
>used by industry..... most kaolins, some red clays, some ball clays, flint,
>spar, pyrophyllite, etc., and stay away from materials that have been know
>to exhibit severe changes over time such as "fireclays" and some red clays.
>Certain "stoneware" clays might fall into this category also. Diversity
>particle sizes as well as choice of materials. It is also important to
>educate oneself.
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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