Ivor and Olive Lewis on mon 24 oct 05
Dear Friends,
I had prepared Three specimens of fine Terra Cotta clay. They were =
wedged by the cut and slam method that builds up uniform thicknessed =
layers of clay. One of the specimens was cut and assembled 20 times, the =
other thirty. May I say this is a good deep breathing exercise.
I cut specimens and ground them flat after they had dried. Today I =
applied a layer of instant adhesive to the edges.
When the film was removed I could see marking but could not discern the =
nature of the texture.
Out with the Microscope ! !
Under a magnification of X-60 I was unable to differentiate any linear =
structure that would be expected in either specimen. This was a big =
disappointment as it would have supported the common sense view.
What I could see in both specimens was a random distribution of sandy =
particles, many of them in contact with each other, embedded in an =
undifferentiated background. The only difference between the two =
specimens was that the one which had been worked to a greater degree =
showed wave undulations.
What concerns me is that, as a teacher, I asked my students to calculate =
the number of individual layers after clay had been treated this way. =
But there is no evidence to support those calculations, no suggestion of =
layering or alignment.
And the white clay which had been Rams Head Kneaded and should have =
exhibited a marked spiral structure did not reveal this when it =
voluntarily fractured during its ageing process. One day I may find =
clear, natural evidence that clay crystals are regimented and ordered by =
work.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Earl Brunner on tue 25 oct 05
This I have seen, and not under a microscope. Working in a city studio with lots of students, one of my jobs is to recycle clay. From time to time I take lumps of dry clay and break them up to slake down for recycling. Some of these lumps of dry clay are rams head kneaded lumps that have been put aside to be used later and have dried out. When they are hit with a hammer they often break up along spiral fracture lines, clearly showing the spiral of the wedging. If thats not alignment of some kind, I don't know what is.
Ivor and Olive Lewis wrote:
Dear Friends,
And the white clay which had been Rams Head Kneaded and should have exhibited a marked spiral structure did not reveal this when it voluntarily fractured during its ageing process. One day I may find clear, natural evidence that clay crystals are regimented and ordered by work.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
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Jim Murphy on tue 25 oct 05
skiasonaranthropos@FSMAIL.NET wrote:
> some rather strange concepts were introduced:
> 1.) Fibres, and fibres with barbs. Where have these concepts come from?
Hi Antony,
I too would have preferred the narrator [with the funny accent] use a
different descriptive term for that initial "zoom". I just "let it go"
though and kept peering deeper into the structure.
> 2.) The suggestion that a clay bowl is held together because its densely
> packed can easily be seen to be false as quartz sand can be made to pack
> densely but that its not going to perform the same as clay
Of course, Antony, densely-packed quartz sand has the disadvantage of NOT
being able to sustain a pore water pressure [as a plastic clay body does].
Put that quartz sand in a rubber bag [ala Norton] and a rudimentary
understanding of "plasticity" emerges.
Kick things up a notch to "Soil Mechanics Theory" and we readily understand
why a "plastic" clay-water system is NOTHING like densely-packed quartz
sand.
Best wishes,
Jim Murphy
Jim Murphy on tue 25 oct 05
Hi Ivor,
Here's an interesting high-zoom video link (the same one I referenced in my
reply to the "Re: S-cracks...is clay actually compressed? Oh yah!" Clayart
topic):
Click on the "clay" icon [bowl] to see a high-zoom (over 12-million x)
"video" of a clay bowl's internal microstructure.
Best wishes,
Jim Murphy
on 10/24/05 3:21 AM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
> One day I may find clear, natural evidence that
> clay crystals are regimented and ordered by work.
William & Susan Schran User on tue 25 oct 05
On 10/24/05 4:21 AM, "Ivor and Olive Lewis" wrote:
> But there is no evidence to support those calculations, no suggestion of
> layering or alignment.
> And the white clay which had been Rams Head Kneaded and should have exhibited
> a marked spiral structure did not reveal this when it voluntarily fractured
> during its ageing process. One day I may find clear, natural evidence that
> clay crystals are regimented and ordered by work.
Ivor - I would not expect the clay platelets to necessarily become aligned
during the cut & slam or spiral wedging process to the extent one could see
them without sufficient magnification, X-60 not being fine enough.
I would expect a more homogeneous mix, one that is more compressed, but the
wedging process may be too "course" a process to align the clay particles.
Wedging and the process of throwing, affecting smaller areas of clay, may
result in the particle alignment.
Perhaps observing the same clay, thrown to a thin wall might reveal a
particle alignment.
I plan some experiments on the "S" cracking issue, using different colors of
a clay body, placed in strategic locations to see what happens.
My suspicions that the major contributors to "S" cracking are multiple: the
clay body itself, lack of compression and/or relationship of bottom to wall
thickness.
--
William "Bill" Schran
Fredericksburg, Virginia
skiasonaranthropos@FSMAIL.NET on tue 25 oct 05
Hello Jim,
Thanks for the link; the video seemed really promising at first but then
some rather strange concepts were introduced:
1.) Fibres, and fibres with barbs. Where have these concepts come from?
2.) The suggestion that a clay bowl is held together because its densely
packed can easily be seen to be false as quartz sand can be made to pack
densely but that its not going to perform the same as clay
I think interesting but not good
Regards,
Antony
Bruce Girrell on wed 26 oct 05
Anthony wrote:
>1.) Fibres, and fibres with barbs. Where have these concepts come from?
Those were not artists conceptualizations, but electron micrographs. They
are not concepts; they are reality.
Our treatment of clay as simple platelets is grossly oversimplified. Some
kaolin has a booklet-like arrangement of plates, but other clays, especially
the ones that we tend to call "plastic" clays, have a much more complex
structure.
Bruce "simple things are rarely as simple as we would like" Girrell
Ivor and Olive Lewis on thu 27 oct 05
Bruce Girrell wrote:
<Some
kaolin has a booklet-like arrangement of plates, but other clays, =
especially
the ones that we tend to call "plastic" clays, have a much more complex
structure.>>
Halloysite Clays the same chemical composition as Kaolinite clays. Yet =
under the influence of water they have the ability to curl up into =
tubular shapes.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
skiasonaranthropos@FSMAIL.NET on thu 27 oct 05
Hello Bruce,
Thank you for your comment, however:The video found at the highlighted
link is an animation rather than electron micrographs. All the many
electron micrographs of kaolinite Ive seen, by far the most common clay
mineral in pottery, show nothing that could be described as fibres let
alone ones with barbs
The crystal shape of clay minerals does vary between species:
Kaolinite: hexagonal platelets
Halloysite: long and thin; often described as needles or tubes
Dickite: platelets
Nacrite: platelets
Montmorillionite: difficult to image but tend towards anhedral
Illite: the only clay mineral that nears something that might be described
as fibrous
The shapes of naturally occuring clay particlese may not always be perfect
geometrically but kaolinite, again the common pottery clay mineral, has a
hexagonal platelet shape: thin platelets thick platelets, stacks of
platelets, books of platelets, verms of platelets, big platelets, thin
platelets but .... platelets!
Regards,
Antony
Bruce Girrell on thu 27 oct 05
Antony wrote:
>The video found at the highlighted
>link is an animation rather than electron micrographs. All the many
>electron micrographs of kaolinite Ive seen, by far the most common clay
>mineral in pottery, show nothing that could be described as fibres let
>alone ones with barbs
Then we have been looking at different clays. I studied clays as an offshoot
of oilfield work long before I started pottery. Clays that I have seen EMs
of are anything but ordered, especially the smectites. They are hairy,
curled, tangled things. Their tortuosity is why smectites have such a huge
surface area.
Bruce Girrell
Michael Wendt on thu 27 oct 05
Bruce noted that the smectites are high surface area.
The SEM images I have seen of some of the clay particles
found in Helmer have edges that look like a coastline with multiple fjords
intruding inward giving the clay
particles much more surface area than a simple flake.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Bruce wrote:
Then we have been looking at different clays. I studied clays as an offshoot
of oilfield work long before I started pottery. Clays that I have seen EMs
of are anything but ordered, especially the smectites. They are hairy,
curled, tangled things. Their tortuosity is why smectites have such a huge
surface area.
Bruce Girrell
skiasonaranthropos@FSMAIL.NET on thu 27 oct 05
Hello Bruce,
That must be it. Under both SEM and TEM most clay minerals reveal their
shape relatively easily whilst I=92ve always struggled with smectites,
mainly montmorillionite, to distinguish any distinctive shape
Regards,
Antony
Ivor and Olive Lewis on fri 28 oct 05
I think this concept was raised a couple of years ago
<<.....densely-packed quartz sand has the disadvantage of NOT being able =
to sustain a pore water pressure [as a plastic clay body does]. Put that =
quartz sand in a rubber bag [ala Norton] and a rudimentary understanding =
of "plasticity" emerges.....>>
Perhaps a Condom full of wet sand may simulate one feature of plastic =
clay and would be more accessible to the mind if it included marbles, =
lead shot or ball bearings to imitate the other constituents of a clay =
body. Put a couple of dozen of these into a bucket and freely lubricate =
with olive oil. When you push the things the mixture must surely imitate =
the plastic condition, behaving like clay flocs, moving, aligning, =
adjusting in shape and sliding. The only think that seems to be missing =
is something to make the stuff go rigid and retain its shape when the =
motive force is removed.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Bruce Girrell on fri 28 oct 05
Antony,
I hope that my response to you did not come off as sounding snotty. What I
had intended to say was that EM images that I am familiar with have been
primarily those associated with "clays in the wild", those retrieved from
core samples, for example. I have not actually seen that many images of
refined clays of the type that we typically would be using for pottery. As a
result, the morphology and complexity of the clay in the animation did not
look unusual to me. I took the term "barbs" more loosely, assuming that the
copy writer was simply not familiar with more appropriate terminology.
As for the animation itself - someone else mentioned the "powers of 10"
videos and when I first looked at this animation I thought that it was done
in the same manner, using actual optical and SEM images with a little
artistic transitioning between the magnification levels. Perhaps that is not
the case here. Maintaining the exact same viewpoint while transitioning from
macro to optical micro to SEM to TEM would indeed be quite a feat.
Bruce Girrell
Tom at Hutchtel.net on sat 29 oct 05
>>>From: "Ivor and Olive Lewis" Subject: Wedged Clay Structure
> adjusting in shape and sliding. The only think that seems to be missing =
> is something to make the stuff go rigid and retain its shape when the =
> motive force is removed.
Isn't this where, theoretically, this electrical attractions between the
clay particles take over?
If what we're talking about in getting closer and closer, maybe the concept
of fractals would be useful...where the larger view actually imitates the
microscopic view. I've seen this when I leave some wet cay out in seriously
sub zero weather. You get this very interesting structure of layers of flat
particles of various sizes...look almost like cliffs of eroded limestone or
shale.
Tom
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