Jon Pacini on fri 7 jan 05
Greetings All--------
I have a tough time putting much stock in a typical chemical analysis
report and living and dieing with it. Not that the variations are always
catastrophic, but that the typical part of the analysis, at least to me
seems very misleading. How can you rely on a bunch of oxide percentages to
do glaze calculation when those percentages don t really reflect what
material is in the bag you re using.
Chemical oxides aren t in the bag, a variable mineral is in the bag.
If I were the King of Ceramics , the information that I would like to see
used more in ceramics than the typical chemical analysis is a physical
mineral composition derived from X ray diffraction. My feeling is that the
chemical analysis we're usually given doesn t really reflect what a mineral
really is. It does not describe how the mineral elements are actually
composed. The more I work with minerals, the more I m convinced that the
physical nature of a mineral is key to how minerals react in a clay or
glaze. Chemical composition is of course important. I wouldn t downplay
that. But there s much more to a mineral than just it s constituent oxides.
An example of this is to look at the attempts to reproduce Gerstley Borate
by oxide reconstruction. Even though you can put all the correct oxides into
a substitute, generally, they yield unsatisfactory results. The same was
true in trying to reproduce Kingman feldspar. You may be able to make a frit
that way, but you can t reproduce a mineral. The subs just wouldn t react
the same way. It's only when similarly 'constructed' minerals are involved
in the substitute that success is achieved. Even that s elusive. This may be
a fine point, but key.
What you find out from diffraction is not just the chemical elements
involved, but what the constituent mineral composition is, how the chemical
elements are actually combined.
I know a lot of people live and die with chemical analysis, but to me it
seems that you may be in the right forest, but you re barking up the wrong
tree.
But then I m not likely to ever be King of Ceramics . And this is just my
opinion for whatever it s worth.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
Hey Phil ---I hear it s snowing in el vee---brrrrrrrrrr.
Daniel Semler on sat 8 jan 05
Hi Jon,
I'm not particularly familiar with what you'd get from XRD. Only seen bits in
some book somewhere. Could you give an example (or pointer to) XRD of something
dirt common eg. some ball clay or spar ? :) I would find it interesting to think
through your proposition.
Thanx
D
>
> If I were the King of Ceramics , the information that I would like to see
> used more in ceramics than the typical chemical analysis is a physical
> mineral composition derived from X ray diffraction. My feeling is that the
> chemical analysis we're usually given doesn t really reflect what a mineral
Dave Finkelnburg on sat 8 jan 05
Jon,
Interesting approach you suggest, using mineral analyses rather than chemical analyses! The ailment you seek to treat is, of course, imperfect ceramics. And you are right, absolutely. Minerals influence fired results! Some questions, though.
Would your suggestion mean clays would be reported as, for example, % kaolinite, % dickite, % nacrite, % halloysite, etc. along with % quartz, % microcline and plagioclase (two of several feldspar minerals), etc? Or, would you lump the kaolin minerals, and then lump the smectites, and then lump feldspars, etc? OR, would you classify the clays as 1:1 sheet silicates, 2:1 sheet silicates, etc and lump the feldspars as soda feldspars, calcium feldspars, potassium feldspars, etc? Or...
When you take X-ray diffraction (XRD) and start investigating clay minerals I think you find that some minerals are as easily defined exactly as the color gray is easily defined on the continuum between black and white. The periodic table of elements has been pretty much agreed upon for some time. The classification of minerals, especially clay minerals, is more of a moving target.
For those who wonder, by the way, XRD bombards a mineral sample with X-rays and records the resulting scattering of the rays. Crystals scatter the rays at specific angles, characteristic of the crystals. This is NOT a totally precise, exact science. However, it is useful for identifying the major crystal types in a sample.
When you become King of Ceramics :-) I submit that it might be more productive to study why our knowledge of the chemistry of, say Gerstley borate, does not permit us to easily compound a frit with exactly the same glaze-producing properties as that mineral. What holds us back? I have a feeling we just don't understand the fundamentals involved.
We know that in a glaze the elements form a glass...BUT, we don't know enough about the mobility of those elements in the glaze melt, the time available for those elements to move around, how widely separated or grouped together the minerals that hold those elements are in the applied glaze.
This doesn't mean we all need to be chemists or engineers or any kind of scientists. But we do need, as potters, more help from the scientists. Glass artists today have such a wonderful variety of high-quality glass for slumping in part because back in 1932 Wm. Zachariasen published a hypothetical model for silicate glass. I didn't need to know a thing about that to slump glass in my electric kiln last week, but I benefitted from the work of Zachariasen and a ton of other glass scientists. We need more of that fundamental science applied to ceramics!
What I am saying is I am convinced that basic chemistry plus thermodynamics, phase equilibria, transport phenomena and surface chemistry, etc, hold the real keys to the understanding you seek. Simply compounding minerals, rather than compounding chemicals, certainly provides some useful insights. At the same time it is a bit like taking cough drops to cure pneumonia. We need to be treating the whole disease of imperfect ceramics, not just dealing with symptoms.
Regards,
Dave Finkelnburg
Jon Pacini wrote:
I have a tough time putting much stock in a typical chemical analysis
report and living and dieing with it. Not that the variations are always
catastrophic, but that the typical part of the analysis, at least to me
seems very misleading. How can you rely on a bunch of oxide percentages to
do glaze calculation when those percentages don t really reflect what
material is in the bag you re using.
Chemical oxides aren t in the bag, a variable mineral is in the bag.
---------------------------------
Do you Yahoo!?
Meet the all-new My Yahoo! – Try it today!
Ron Roy on sat 8 jan 05
Hi John,
Anyone who says this is not working with calculation software - other wise
you would have another point of view.
It is also true - with most materials - that that minor variations in raw
materials will hardly ever show up in a glaze. If you know which materials
do vary a lot - such as GB then you can build that into a line bend and
still get good answers..
Waiting for better analysis is simply not necessary - what we have now are
working just fine - at least for me they are. I don't take anyone's word
for analysis by the way - I try to deal directly with the mine whenever I
can.
I do notice - when working on clay and glazes - the clays and glazes that
are most difficult to deal with are those with fewer materials rather than
a lot. It is never a bad policy to use as many different materials as you
can - especially if you don't know which are steady and which are not.
In the end - even if calculation is not a perfect tool - it is still far
and away the best tool we have for the job - unless guessing is considered
better.
Then there is the situation when the worker blames the tool because they
don't have the skill to make it work - and I think we - as a group are
learning how to use it with the attendant frustrations that go along with
that process.
I have checked all the GB substitutes and I could not understand what went
wrong - only one (Gillespie Borate) came close to the original - does it
mean those who tried to duplicate it started with the wrong analysis - or
did not know how to use calculation software to get close to the original -
or could not get it right with the materials they decided to use - or all
three.
In the end the oxides are in the bag - and they always vary at lease a
little bit - it is also true that the usual variation just does not make
any difference in the great majority of clay bodies and glazes - unless
they are poorly formulated by those who don't know their materials.
Blaming the materials we use is a losing proposition - we should be more
knowledgeable about the basic materials we use. Unless of course you enjoy
paying the price of ignorance every once in a while.
RR
>I have a tough time putting much stock in a typical chemical analysis
>report and living and dieing with it. Not that the variations are always
>catastrophic, but that the typical part of the analysis, at least to me
>seems very misleading. How can you rely on a bunch of oxide percentages to
>do glaze calculation when those percentages don t really reflect what
>material is in the bag you re using.
>
>Chemical oxides aren t in the bag, a variable mineral is in the bag.
>
>If I were the King of Ceramics , the information that I would like to see
>used more in ceramics than the typical chemical analysis is a physical
>mineral composition derived from X ray diffraction. My feeling is that the
>chemical analysis we're usually given doesn t really reflect what a mineral
>really is. It does not describe how the mineral elements are actually
>composed. The more I work with minerals, the more I m convinced that the
>physical nature of a mineral is key to how minerals react in a clay or
>glaze. Chemical composition is of course important. I wouldn t downplay
>that. But there s much more to a mineral than just it s constituent oxides.
>
>An example of this is to look at the attempts to reproduce Gerstley Borate
>by oxide reconstruction. Even though you can put all the correct oxides into
>a substitute, generally, they yield unsatisfactory results. The same was
>true in trying to reproduce Kingman feldspar. You may be able to make a frit
>that way, but you can t reproduce a mineral. The subs just wouldn t react
>the same way. It's only when similarly 'constructed' minerals are involved
>in the substitute that success is achieved. Even that s elusive. This may be
>a fine point, but key.
>
>What you find out from diffraction is not just the chemical elements
>involved, but what the constituent mineral composition is, how the chemical
>elements are actually combined.
>
>I know a lot of people live and die with chemical analysis, but to me it
>seems that you may be in the right forest, but you re barking up the wrong
>tree.
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 sun 9 jan 05
Dear Dave,
Well said !!
I hope those who think Science and Technnology and the knowledge they
bring to us are not for artistic people. They should heed of your
words.
As I said previously, it would not have been possible to propose a new
chemistry for Salt Galzing with Sodium Chloride without knowing about
the residual minerals that are present in clay.
Knowing about residual substances and the variations in quality of raw
material over time as well as the processes used to keep consistency
in batch production helps us to have confidence in the products we buy
from our suppliers.
Now here is something else to think about. What murky secrets are
concealled in those three letters "..L-O-I.."
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ivor and Olive Lewis on sun 9 jan 05
Dear Daniel Semler,
The journal "Interceram" often features research papers which provide
illustrations of X-Ray Diffraction Spectra. There is a paper relating
to Cobalt Alumina Spinel type compounds in July, 4-2002, Vol 51.
which has several XRD plots.
The idea is that a mix of minerals gives a characteristic
"Fingerprint" with the marker for each mineral in a constant position.
The amount of each mineral is related to the height the spike it gives
so this is a good way to assess consistency of samples like a clay or
other natural mineral mixture. With a few thousand dollars you can be
the proud owner of a shiny Phillips job.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Jon Pacini on mon 10 jan 05
Greetings All------ Hi Ron-----
I would have to agree with your closing statements that blaming materials is
a losing proposition, as is working with them in ignorance.
And I would have bet the farm you'd say that glaze calculation supports the
point of view that, "the oxides are in the bag", and that the status quo in
analysis works just fine for you.
Over the years I've had many Ceramic Engineers as colleagues as well as
others who used oxide calculation to formulate clays and glazes. They spent
quite a bit of time doing their calculations and yet always seem to have to
run as many or more tests as I, or my colleagues who didn't use calculation.
In the end they still have to fire the samples and tweak the tests till
geting the performance they wanted.
I have always felt this was due to variations in the minerals from what was
published as the composition. After all, if the numbers are all correct,
then calculation should give you the desired results, but they rarely did
for my calculation minded colleagues.
Granted now a days you can cut calculation time down to next to nothing with
glaze software and it will get you in the ballpark, but calculation is still
no substitute for knowing the how minerals work the way they do. A method
I've always preferred, which has nothing to do with guessing. I've never
understood why you would bother with calculation unless you had no clue as
to what minerals did when you fired them.
Yes, I've heard the argument that in order to develop ceramics within
specific oxide limits you have to use calculation. I guess if you're into
'engineering' this would be a good thing.
I just don't think it has much to do with the reality of what's in the bag.
Something else we will have to agree to disagree on.
As for the Gerstley subs, I was always looking forward to putting Laguna
Borate 2 on the market. It would have been a much better material than the
first one. But that's another story.
In developing Laguna Borate I did at one point employ computer soft ware to
give me options of what to use as the building blocks for the substitutions.
I never really found it a very satisfactory method. Though I could get a
material that would create fluxing in the same manner as Gerstley, results
varied wildly on what specific minerals combinations were employed. Even
though they would "oxide wise" be the same as Gerstley. I went through the
same thing back in the '70's when Kingman feldspar went off the market and
when Colemanite went south. Calculation just never seemed to get the results
quite right. You always have to find the correct combination of minerals
that work regardless of what the oxide calculation said.
I'm going to be off list for a week starting tomorrow---- Driving up to
Mendocino for the Potters Council get together. Take my time and visit some
along the way. You guys get a few free shots till I get back---- have fun.
:)
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
| |
|
