iandol on sun 11 jan 04
Dear Friends,
I know a specific question was raised by Chris Clyburn her concerns do =
raise a series of general issues concerning our understanding of the =
materials involved, the processes they go through, the problems that =
arise during manufacture and use and the formulation of solutions to =
problems which happen from time to time.
What are the fundamental design concerns? Perhaps integrity is the first =
to come to mind. The chosen formulation should lead to a product which =
will do the job, which meets the intended specification.
It must lead to a vitreous fabric and though it may contain some degree =
of "void space", a term I prefer to the commonplace "Porosity" which =
implies the ability to adsorb and exude water.
Its ingredients must not cause a body to deflocculate, a cause of =
flabbiness which can prevent achievement of form due to lack of physical =
strength.
It must mature with no free crystalline silica which imposes stress due =
to phase changes. Such stress development can destroy a pot during =
processing or at a later date..
Given that this is just a meagre start, what else would anyone add to =
ensure that the clay you select to prepare for your own use will fulfil =
your intended functions ??
Thinking about setting Standards !!!
Best regards,
Ivor Lewis. Redhill, South Australia
Chris Clyburn on tue 13 jan 04
Ivor,
I personally would like to make one that functions equally well for
handbuilding and throwing, but contains as little grog or sand as possible
so it hold detailed carvings yet enough to have the body strength to throw
at least into the medium size range (12-25 inches IMHO)
The only other thing I would add would be that my wife and I checked, and
agree that I am assuredly a "him"
Chris Clyburn
Chris
On Sun, 11 Jan 2004 17:26:31 +1030, iandol wrote:
>Dear Friends,
>I know a specific question was raised by Chris Clyburn her concerns do
raise a series of general issues concerning our understanding of the
materials involved, the processes they go through, the problems that arise
during manufacture and use and the formulation of solutions to problems
which happen from time to time.
>What are the fundamental design concerns? Perhaps integrity is the first to
come to mind. The chosen formulation should lead to a product which will do
the job, which meets the intended specification.
>It must lead to a vitreous fabric and though it may contain some degree of
"void space", a term I prefer to the commonplace "Porosity" which implies
the ability to adsorb and exude water.
>Its ingredients must not cause a body to deflocculate, a cause of
flabbiness which can prevent achievement of form due to lack of physical
strength.
>It must mature with no free crystalline silica which imposes stress due to
phase changes. Such stress development can destroy a pot during processing
or at a later date..
>Given that this is just a meagre start, what else would anyone add to
ensure that the clay you select to prepare for your own use will fulfil your
intended functions ??
>Thinking about setting Standards !!!
>Best regards,
>Ivor Lewis. Redhill, South Australia
>
>______________________________________________________________________________
>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.
iandol on wed 14 jan 04
Dear Chris Clyburn,=20
Sorry for the Faux Pas. No offence intended by the way. I just imagined =
"Christine" and penned my remarks in tune with that notion.
I work with commercial bodies which are very fine and have no difficulty =
in getting the sort of heights you intend making. contrary to popular =
opinion I do not believe that grog and such like "non plastic additives" =
add strength to a clay body and so make it better able to "Stand Up"
I wish you success in your quest and give my kind regards to y our wife.
Best regards,
Ivor Lewis. Redhill, South Australia
Antoinette Badenhorst on thu 15 jan 04
Hallo Ivor. This is a very interesting remark that you made about non
plastic materials in claybodies. Would you mind saying a bit more on
this.
I recently added bentonite to my upcoming claybody to bring strengh to
the body, but I used mullite to open the body and to work against too
much shrinkage and warping. Have not tested it yet.
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 iandol
Sent: Wednesday, January 14, 2004 12:59 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Designer Clay Bodies
Dear Chris Clyburn,
Sorry for the Faux Pas. No offence intended by the way. I just imagined
"Christine" and penned my remarks in tune with that notion.
I work with commercial bodies which are very fine and have no difficulty
in getting the sort of heights you intend making. contrary to popular
opinion I do not believe that grog and such like "non plastic additives"
add strength to a clay body and so make it better able to "Stand Up"
I wish you success in your quest and give my kind regards to y our wife.
Best regards,
Ivor Lewis. Redhill, South Australia
________________________________________________________________________
______
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.
iandol on sat 17 jan 04
Dear Antoinette Badenhorst,=20
I knew some one would pick me up on that one. It all depends on what you =
believe about the nature of clay and the cause of plasticity. My own =
view is that clay is plastic because of the altered behaviour of water =
when it is influenced by kaolinite clays. I do not believe it is about =
the sliding action between clay particles lubricated by water, as =
described in many popular text books.
A strong clay is about an optimum relationship between the mass of water =
and the mass of the mineral which interacts with the water to cause =
plasticity. The strength of our plastic medium depends upon the power of =
the water. Remove that influence, by drying, by saturating, or by =
decreasing the proportion of water and you get a weaker plastic clay =
body. Grog and non plastic materials cause drying or dilution which =
leads to a loss of strength.
Some time ago I described a Magnetic Model for plastic clay. Those =
people who have taken the time and gone to the trouble to make that =
model will find, if they intermix a non-magnetic material into the =
Magnet/Iron Powder mixture, such as polystyrene balls, that the =
integrity of the mixture is compromised.
Yes, Bentonite is a popular additive introduced into short clays to =
enhance plasticity. But the physical properties invoked to achieve this =
property differ from the physical properties of Kaolinite or Ball Clay.
Good to hear from you again and to know you are making happy progress.
Best regards,
Ivor Lewis. Redhill, South Australia
Antoinette Badenhorst on mon 19 jan 04
Hi Ivor. If you could see me now you would see a big frown on my face. I
have one thousand questions for you now. How does kaolinite alter the
behavior of the water? The sliding action description is the one that I
found logical and taught my students over the years. Say this is wrong,
how you explain cracks in pots (eg. S-cracks) and how do you explain
tired/overworked clay.
Your explanation of the relationship between clay minerals and water
makes sense to me, since as clay becomes bone dry it also becomes more
fragile. If there is not enough "glue"(clay) to keep the particles
together, it will crumble. It also sounds logical that non plastic
materials will absorb the water, which allows the clay to dry more
evenly. In my view that is the more important function of these
non-plastic materials. As far as adding grog to the strength of clay is
concerned, I was always under the impression that the grog packs
together like little bricks that is stacked on top of each other to
build a wall, but grog without enough plastic clay to act as "glue",
will not be strong.
I missed the postings about the magnetic models. Maybe I will find that
info in the archives.
Bentonite raised some questions from me lately. I always mixed it into
other raw materials and never mixed it by itself into water before. A
few weeks ago I wanted to add some to a wet clay mixture and realized
that it would make lumps if I do not mix it in wet, so I mixed it with
water. It took quite some time for the water to soak through, which I
believe is due to the fine particle size, but then, it almost became
transparent on my fingertips and it also looked like pudding/jelly. That
raised all my questions about this material. It would be interesting to
know more about bentonite and to know to which raw material group it
belongs.
One last thing....quite some time back you asked me where I found the
info about hydraulic (I hope this spelling is correct) water that is
around clay particles. This water only evaporates during the bisque
process. I found that info again. It is in the Thames and Hudson Manual
of Pottery and Ceramic.
Thanks for your input on Clayart. It is always good to read your
comments.
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS
38866
662 869 1651
www.clayandcanvas.com
Undetermined origin c/o LISTSERV administrator on wed 21 jan 04
Dear Antoinette,
So many questions.
<> It stops it =
from being a liquid. Lawrence and West explain this without getting into =
the details of molecular structure. They use a term "Water Hull" whose =
origin I do no know. In its ideal plastic state there is no liquid water =
in your clay bodies.
<> Free movement is =
prevented by places which have become rigid. But the drying clay =
continues to loose water and the particles of clay move closer together. =
This build up a Tensional Stress in the less firm clay. When imposed =
stress is greater than tensile strength the fabric tears.=20
<< how do you explain tired/overworked clay.>> Here the principle cause =
is the loss of superfine clay particles which you wash from clay as it =
is being thrown. This is what becomes that mass of slurry in the wheel =
pan. The ratio of Plastic to non plastic ingredients is being reduced. =
Slurry should be back mixed with reclaimed clay or replaced with a ball =
clay or plastic Kaolin. But this may only be a problem in a communal =
workshop or a teaching situation where clay has to be recycled. In a =
production situation there should be almost no reclaim except where the =
work demands a lot of turning. But then, the cause is not present is it?
<makes sense to me, since as clay becomes bone dry it also becomes more =
fragile. If there is not enough "glue"(clay) to keep the particles =
together, it will crumble.>> This is a perceptive statement. Just what =
is it that holds the solids together in green clay? I can think of =
several but perhaps other Clayarters may like to give their opinions. As =
I see it Clay is not the"Glue". There are other factors which need to =
be considered but, for the time being I think the principle adhesive is =
Water. More than that I am not prepared to say on the list.=20
<water, which allows the clay to dry more evenly.>> Except where bisque =
grog, porous crushed sandstone or Bentonite are introduced into a body =
all of the other solids are impervious and hold no water within their =
structure. Drying of clay is a complex process which is hard to explain =
in simple terms in a short space of time.
<little bricks that is stacked on top of each other to build a wall, but =
grog without enough plastic clay to act as "glue", will not be strong.>> =
Not enough is known about this either. People seem to make guesses =
based on ideas that come into their imagination. These are translated =
into some interesting art work which s published in our text books. But =
do they represent facts or pure conjecture? Now that I have most of the =
equipment I may be able to image clay that has been worked in various =
ways but it could be a long term project.
<that info in the archives. >> I made a model from small magnets and =
very fine iron powder as an analogy for plastic clay. Magnets represent =
the clay crystals and fragments of iron powder represent water =
molecules. This system mimics the Force relationships we are dealing =
with, something other commentators have ignored. When you get to about =
twenty magnets the mixture of magnets and powder become plastic and =
deforms plastically. When internal resistance is overcome the material =
moves and retains its new shape after the force is terminated. As there =
has been so little comment about this analogy I assume the artistic =
community is disinterested in knowing about the technology of their art =
and craft.
Wishing you a Happy New Year with many prosperous and creative =
interludes.
Best regards,
Ivor Lewis. Redhill, South Australia
=20
Antoinette Badenhorst on wed 21 jan 04
Ivor, thanks for your time. I think I have to go read more on this. You
throw the whole old theory off the table, which throws some of my
logical understanding out the door. I do agree with you that water plays
a very important role and without water no clay, no matter how fine the
particle structure, will be plastic. But, say for instance I take kaolin
and ball clay and mix it separately with equal amounts of water. If I
test it for plasticity, the ball clay will be plastic and the kaolin
will be less plastic....right? If I mix the two together I will get a
more plastic mass than just the kaolin and less plastic than just the
ball clay. What is the reason for this?
As far as my little bit of knowledge goes, clay does not just get
overworked by working it with water. I've seen it before many times with
beginner students, to which my first assignment is always pinch pots. I
do not allow them any water, except a damp sponge to dampen their hands
with. Often their inexperience leads to break up of a pot, wetting and
wedging the clay again and starting the pinching process all over again.
If this happens too many times with the same piece of clay, the clay
becomes tired and no one can use it till it rested for at least a day.
How, in your view does that happen?
This theory of yours will also influence slip casting slip (or for the
sake of the case, terra sigilata), of which I know even less. Why would
one use materials like sodium silicate to keep the clay particles in
suspension? (Whoa...I start feeling like a amateur working with life
electricity!)
By the way....you put your foot in this, now you have to bear my
questions! :-)
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
Undetermined origin c/o LISTSERV administrator
Sent: Tuesday, January 20, 2004 11:01 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Designer Clay Bodies
Dear Antoinette,
So many questions.
<> It stops it
from being a liquid. Lawrence and West explain this without getting into
the details of molecular structure. They use a term "Water Hull" whose
origin I do no know. In its ideal plastic state there is no liquid water
in your clay bodies.
<> Free movement is
prevented by places which have become rigid. But the drying clay
continues to loose water and the particles of clay move closer together.
This build up a Tensional Stress in the less firm clay. When imposed
stress is greater than tensile strength the fabric tears.
<< how do you explain tired/overworked clay.>> Here the principle cause
is the loss of superfine clay particles which you wash from clay as it
is being thrown. This is what becomes that mass of slurry in the wheel
pan. The ratio of Plastic to non plastic ingredients is being reduced.
Slurry should be back mixed with reclaimed clay or replaced with a ball
clay or plastic Kaolin. But this may only be a problem in a communal
workshop or a teaching situation where clay has to be recycled. In a
production situation there should be almost no reclaim except where the
work demands a lot of turning. But then, the cause is not present is it?
<makes sense to me, since as clay becomes bone dry it also becomes more
fragile. If there is not enough "glue"(clay) to keep the particles
together, it will crumble.>> This is a perceptive statement. Just what
is it that holds the solids together in green clay? I can think of
several but perhaps other Clayarters may like to give their opinions. As
I see it Clay is not the"Glue". There are other factors which need to
be considered but, for the time being I think the principle adhesive is
Water. More than that I am not prepared to say on the list.
<water, which allows the clay to dry more evenly.>> Except where bisque
grog, porous crushed sandstone or Bentonite are introduced into a body
all of the other solids are impervious and hold no water within their
structure. Drying of clay is a complex process which is hard to explain
in simple terms in a short space of time.
<little bricks that is stacked on top of each other to build a wall, but
grog without enough plastic clay to act as "glue", will not be strong.>>
Not enough is known about this either. People seem to make guesses
based on ideas that come into their imagination. These are translated
into some interesting art work which s published in our text books. But
do they represent facts or pure conjecture? Now that I have most of the
equipment I may be able to image clay that has been worked in various
ways but it could be a long term project.
<that info in the archives. >> I made a model from small magnets and
very fine iron powder as an analogy for plastic clay. Magnets represent
the clay crystals and fragments of iron powder represent water
molecules. This system mimics the Force relationships we are dealing
with, something other commentators have ignored. When you get to about
twenty magnets the mixture of magnets and powder become plastic and
deforms plastically. When internal resistance is overcome the material
moves and retains its new shape after the force is terminated. As there
has been so little comment about this analogy I assume the artistic
community is disinterested in knowing about the technology of their art
and craft.
Wishing you a Happy New Year with many prosperous and creative
interludes.
Best regards,
Ivor Lewis. Redhill, South Australia
________________________________________________________________________
______
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.
Andrew Sugden on wed 28 jan 04
My apologies for coming into this debate a little late but I was intrigued
by the comment "... as clay becomes bone dry it also becomes more
fragile." Could you elaborate? I'm just a little puzzled as reducing the
mositure content of a clay / clay body increases its mechancial strength.
Regards,
Andrew
Antoinette Badenhorst on thu 29 jan 04
Andrew, if your clay is bone dry(or on it's way there, it will break or
crack with a shock action, like when you would drop it or bump it
against something.
And that raises another question: what give one clay body a better green
strength than another?
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 Andrew
Sugden
Sent: Wednesday, January 28, 2004 1:10 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Designer Clay Bodies
My apologies for coming into this debate a little late but I was
intrigued
by the comment "... as clay becomes bone dry it also becomes more
fragile." Could you elaborate? I'm just a little puzzled as reducing the
mositure content of a clay / clay body increases its mechancial
strength.
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.
Andrew Sugden on fri 30 jan 04
Dear Antoinette,
Thank you for taking the time to answer my minor query - I was a little
confused over the use of 'fragile.' Semantics perhaps but seeking
clarfification is better than misunderstanding.
Your comment "What gives one clay body a better green strength than
another?" got me thinking, and, during a quiet lunch today I came up with -
First a definition - Mechanical strength is that property that enables a
material to withstand mechanical stresses without fracture.
Whilst many factors influence the measured strength values of clay bodies
in common with many properties in ceramics it is greatly influenced by -
=84h Particle distribution
=84h Particle size
=84h Particle alignment
Going a little further -
Clay mineral type - The inclusion of some non-kaolinite clay minerals,
such as montmorillionite or halloysite,with the kaolinite in the body is
likely to be lead to increased mechanical strength. Of course the reasons
why is, perhaps, drifting away from the point.
Clay:Non-plastics ratio - Increasing the clay content of a body generally
increases the green strength.
Particle distribution & packing density - Voids, or pore spaces,
offer no resistance to mechanical strength. Therefore maximum strength is
achieved at maximum packing density, ie. when voids are minimised.
Particle size - Increasing the proportion of small particles increases
the overall surface area, hence the cohesive forces, and so strength is
enhanced; which is why generally ball clays are stronger than kaolins.
Delamination - The extent to which the kaolinite stacks are delaminated,
i.e. de-agglomerated, can have a significant effect. This is a major
reason why pugged bodies have increased strengths, and plasticity. (The
trend continues with re-pugging up to an optimum)
Preparation technique - Whilst not a material property it can have a
profound influence. For example the increased particle alignment found in
cast specimens leads to lower strengths than those of identical geometry
formed by extrusion.
Moisture content - Green strength increases as moisture decreases.
Flocculation - Flocculation of a clay by Ca2+ or Mg2+, replacing Na+ or
K+, results in decreased strength. It can therefore be seen that water, or
at least its chemistry, can be an influence.
If anyone else has anything to contribute I'd be very interested.
Regards,
Andrew
Ivor and Olive Lewis on fri 30 jan 04
Dear Antoinette,
You ask <another?>>
I would be interested to read what Andrew has to say in reply.
But I think the simple answer is "Water". But that takes a lot of
explaining.
Best regards,
Ivor Lewis. Redhill, South Australia
Ron Roy on sun 1 feb 04
Hi Andrew,
I tend to agree and can add a little.
Adding 35 mesh Kyanite - needle like crystals really improves dry strength
- mechanically even after firing - As do paper or glass fibers as long as
they are unfired?
Your statement re flocculation and decreased strength - deflocced means
disoriented crystals - flocculation means oriented particles - should not
the later have more strength? or do you have tests to prove the opposite?
Regards - RR
>Thank you for taking the time to answer my minor query - I was a little
>confused over the use of 'fragile.' Semantics perhaps but seeking
>clarfification is better than misunderstanding.
>
>Your comment "What gives one clay body a better green strength than
>another?" got me thinking, and, during a quiet lunch today I came up with -
>
>First a definition - Mechanical strength is that property that enables a
>material to withstand mechanical stresses without fracture.
>
>Whilst many factors influence the measured strength values of clay bodies
>in common with many properties in ceramics it is greatly influenced by -
>
>=84h Particle distribution
>=84h Particle size
>=84h Particle alignment
>
>
>Going a little further -
>
>Clay mineral type - The inclusion of some non-kaolinite clay minerals,
>such as montmorillionite or halloysite,with the kaolinite in the body is
>likely to be lead to increased mechanical strength. Of course the reasons
>why is, perhaps, drifting away from the point.
>
>Clay:Non-plastics ratio - Increasing the clay content of a body generally
>increases the green strength.
>
>Particle distribution & packing density - Voids, or pore spaces,
>offer no resistance to mechanical strength. Therefore maximum strength is
>achieved at maximum packing density, ie. when voids are minimised.
>
>Particle size - Increasing the proportion of small particles increases
>the overall surface area, hence the cohesive forces, and so strength is
>enhanced; which is why generally ball clays are stronger than kaolins.
>
>Delamination - The extent to which the kaolinite stacks are delaminated,
>i.e. de-agglomerated, can have a significant effect. This is a major
>reason why pugged bodies have increased strengths, and plasticity. (The
>trend continues with re-pugging up to an optimum)
>
>Preparation technique - Whilst not a material property it can have a
>profound influence. For example the increased particle alignment found in
>cast specimens leads to lower strengths than those of identical geometry
>formed by extrusion.
>
>Moisture content - Green strength increases as moisture decreases.
>
>Flocculation - Flocculation of a clay by Ca2+ or Mg2+, replacing Na+ or
>K+, results in decreased strength. It can therefore be seen that water, or
>at least its chemistry, can be an influence.
>
>
>
>
>If anyone else has anything to contribute I'd be very interested.
>
>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
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Craig Edwards on sun 1 feb 04
Andrew: That is a sweet analysis of the ins and outs of Mechanical=20
strength. Well stated!
Craig Edwards
New London MN
http://www.livejournal.com/~smilingpotter/
>>Thank you for taking the time to answer my minor query - I was a little
>>confused over the use of 'fragile.' Semantics perhaps but seeking
>>clarfification is better than misunderstanding.
>>
>>Your comment "What gives one clay body a better green strength than
>>another?" got me thinking, and, during a quiet lunch today I came up wi=
th -
>>
>>First a definition - Mechanical strength is that property that enables=
a
>>material to withstand mechanical stresses without fracture.
>>
>>Whilst many factors influence the measured strength values of clay bodi=
es
>>in common with many properties in ceramics it is greatly influenced by =
-
>>
>>=84h Particle distribution
>>=84h Particle size
>>=84h Particle alignment
>>
>>
>>Going a little further -
>>
>>Clay mineral type - The inclusion of some non-kaolinite clay minerals,
>>such as montmorillionite or halloysite,with the kaolinite in the body i=
s
>>likely to be lead to increased mechanical strength. Of course the reaso=
ns
>>why is, perhaps, drifting away from the point.
>>
>>Clay:Non-plastics ratio - Increasing the clay content of a body genera=
lly
>>increases the green strength.
>>
>>Particle distribution & packing density - Voids, or pore spaces,
>>offer no resistance to mechanical strength. Therefore maximum strength =
is
>>achieved at maximum packing density, ie. when voids are minimised.
>>
>>Particle size - Increasing the proportion of small particles increases
>>the overall surface area, hence the cohesive forces, and so strength is
>>enhanced; which is why generally ball clays are stronger than kaolins.
>>
>>Delamination - The extent to which the kaolinite stacks are delaminate=
d,
>>i.e. de-agglomerated, can have a significant effect. This is a major
>>reason why pugged bodies have increased strengths, and plasticity. (The
>>trend continues with re-pugging up to an optimum)
>>
>>Preparation technique - Whilst not a material property it can have a
>>profound influence. For example the increased particle alignment found =
in
>>cast specimens leads to lower strengths than those of identical geometr=
y
>>formed by extrusion.
>>
>>Moisture content - Green strength increases as moisture decreases.
>>
>>Flocculation - Flocculation of a clay by Ca2+ or Mg2+, replacing Na+ o=
r
>>K+, results in decreased strength. It can therefore be seen that water,=
or
>>at least its chemistry, can be an influence.
>>
>>
>>
>>
>>If anyone else has anything to contribute I'd be very interested.
>>
>>Regards,
>>
>>Andrew
>>
>> =20
>>
> =20
>
Antoinette Badenhorst on mon 2 feb 04
Hi Ivor. I think it is time for me to go read more about clay before I
ask more questions. Someone advised me to read "Ceramic Science for the
Potter, 2nd Edition" by Lawrence and West.
I have to admit that this whole thing is throwing me off my "little
bitty knowledge throne" and I do like to understand things logically.
Not having a chemistry background is making it more difficult for me to
understand the bits and pieces as it is addressed here on clayart.
I do have a different concern about all these "popular" books that you
referred to before. If the information out there is not correct, it
needs to get under our attention and we should request the authors to
correct that. I know it is difficult to find the right literature and in
particular authentic literature, but we still need to try.
Regards.
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 Ivor and
Olive Lewis
Sent: Thursday, January 29, 2004 11:59 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Designer Clay Bodies
Dear Antoinette,
You ask <another?>>
I would be interested to read what Andrew has to say in reply.
But I think the simple answer is "Water". But that takes a lot of
explaining.
Best regards,
Ivor Lewis. Redhill, South Australia
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Andrew Sugden on mon 2 feb 04
Thanks everyone for your comments. For me the recent posts illustarte hwo
valuable Clayart can be: excahnge of ideas and get the brain cells working.
And in repsonse to Ron's point re. flocculation and the effect on
strength. If we ignore the non-plastics component: a flocculated clay
suspension is likely to have lower packing density than when
deflocculated. Sorry but I'd like to sketch something but the classic
description of 'house of cards' structure of the flocculated state is the
best I can do in text i.e. edge to face arrangements. Poor packing -> more
gaps -> weaker mechanically.
Wouldn't it be great if we could shrink down molecular level and directly
observe these actions!
Open to comment again....
Andrew
wayneinkeywest on mon 2 feb 04
My goodness, Andrew! Not I! It would be like trying to dodge
a herd of bicycle messengers careening down 42nd Street
during Evening rush hour New Year's Eve in New York!
Or perhaps the running of the bulls in Pamplona!
(Except they all run in the same general direction.)
No thank you!. I'll take the geniuses words for it!
Wayne Seidl
> Wouldn't it be great if we could shrink down molecular level and
directly
> observe these actions!
>
> Open to comment again....
>
>
> Andrew
daniel on mon 2 feb 04
Hi Andrew,
> And in repsonse to Ron's point re. flocculation and the effect on
> strength. If we ignore the non-plastics component: a flocculated clay
> suspension is likely to have lower packing density than when
> deflocculated.
>
This seems to me at least mildly counter-intuitive. I thought that the
result of flocculation was a drawing together of particles which seems (at
least at the macro level ) to imply a tigher structure. Could you explain
more what reduces the packing density ? Perhaps it is related to what you
describe as a suspension ? What exactly is that in this case ?
Thanx
Daniel
Ivor and Olive Lewis on tue 3 feb 04
Dear Andrew Sugden,
Perhaps you missed my postings on an model which presents an analogy
of the Clay Water System and demonstrates, on a hold in your hand and
play with it basis, Plastic Properties.
This Model is easy to construct with pure Iron Powder at minus 100
mesh from a Chemical Supply House and small flat Isotropic Ferrite
Magnets from Radio Shack or Tandy.
I am waiting for someone else to put some money on the table and buy
the necessary ingredients to test my assertion that this is one of the
best models you could ever use to represent the qualities of those
microscopic particles of Kaolinite and molecules of water. Not only
does it model the material ingredients it provides a model of the
Electronic Forces which bind clay to water or water to clay as well as
giving physical form to the Water Hull postulated by Lawrence and West
in "Ceramic Science for the Potter"
"House of Cards" is an interesting concept but only models the Clay
Crystals, and the true form used in the real model is Rectangular
though Hamer shows Hexagonal shapes.
You have a go at making my model.
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on tue 3 feb 04
Dear Antoinette Badenhorst,
Strange thing about Lawrence and West and "Ceramic Science for the
Potter" The first edition was written before W. E. Brownell wrote,
"Structural Ceramics" and the 2nd Ed after. All three books are
useful. But, as Scientists I think Lawrence and West wrote for Artists
where as Brownell wrote for the Common Working Factory Hand. But
Brownell make the Science more accessible.
It is not necessary to have a background in chemistry to read what
each author says. But you do need a mind which is willing to sort out
information, then evaluate what you are being told.
Your comment about popular books should be a concern for all of us.
About an authoritative old friend who taught me much about the craft
of cutting gemstones it was said "Eighty percent of the time he is
absolutely right but the other twenty percent he has no idea he is
wrong". Though the proportions may vary, the same might be said of
those authors who do not cross reference their second hand knowledge.
They should test their thoughts in some way to prove what they are
writing can be corroborated. In addition, their work should be edited
by critical minds before they publish.
Some years ago when I was sorting out Salt Glaze Chemistry I wrote to
Dr Lawrence about information he and Dr West had published. Two points
emerged. First, that the book would not be revised again, second that
the chemistry given was conjectural (Ceramic artists accept it as Fact
! ! ) . I expect similar things would happen if you were to contact
those authors who's writing you question. And, as was pointed out
recently when someone wanted to get in touch with a popular author, we
are human with a limited life span.
Antoinette, read everything you can lay your hands too and feast your
eyes upon. Look for inaccuracies, inconsistencies. assumptions,
assertions, conjectures and Pure Fiction. Cross reference, compare and
contrast. Ask all the questions 5.W+H. When you find something which
annoys you, raise it as an issue in any or all of the public forums
available. I support your right to do that even if I disagree with
what you may say.
Best regards,
Ivor Lewis. Redhill, South Australia
Andrew Sugden on tue 3 feb 04
Hello Daniel,
Thank you for taking the time to consider my comments and I apologise now
for my long reply which I hope gives a fuller expanation of the latter
point of my list of factors:
The idealised shape of a kaolinite crystal is a thin hexagon which are
commonly referred to as platelets. Typical widths of 0.05 to 1 =83=DDm have
been measured with a thickness of around a twentieth of this.
Charges of a platelet
Edge: As the edge of the platelet is formed where the atomic structure
ends broken valency bonds exist. Depending on where these broken bonds
occur effects the charge, and consequently the edge of a platelet has both
positive and negative charges.
Face: Although broken bonds are not found the faces have a negative
charge due to Isomorphous substitution: With Al and Si ions being
relatively similar in size to a number of other metal atoms it is possible
for these to be replaced, such as by Al3+, Fe2+, Mg2+, or Ca2+, without
major disruption of the crystal structure. This results in results in a
charge imbalance that leaves the particle negatively charged overall.
Cation exchange capacity
To achieve electrical neutrality cations can be adsorped on the surface of
particles, these are called exchangeable cations. The extent isomorphous
substitution varies in different clay minerals, described as the cation
exchange capacity or CEC, and is affected by the disorder of the
structure. The CEC and the type of cation significantly influence
properties.
Adsorbed water layer
Water is a dipole, that is a molecule which is overall electrically
neutral but has two regions of opposing charge. The hydrogen atoms of
water are consequently attracted to the hydroxyls of the clay. This allows
a layer of water to form around the clay particle that has a more regular
structure that that of free water into which it gradually merges.
The thickness of the adsorbed water layer thickness is inversely
proportional to the electrolyte concentration of the surrounding water.
The clay particle requires a set number of adsorbed cations for electrical
neutrality, and these must be in diffusion equilibrium with the free
water. As the free water electrolyte concentration increases, so must that
of the adsorbed water layer, and therefore a thinner adsorbed water layer
results.
Divalent cations, such as Mg2+ and Ca2+, result in a thinner adsorbed
water layer than monovalent cations, like Na+ and K+. Twice as many
monovalent ions are needed for electrical neutrality, and therefore for
comparable ion concentrations, a thicker adsorbed water layer will
therefore be required.
Flocculation
Where conditions promote a thin adsorbed water layer the positive edges of
the clay particle may approach close enough to the negative face to form
an electrostatic bond. The structure formed by this edge to face
attraction forms is commonly described as being like a house of cards.
Deflocculation (or dispersion)
With particles having a thick adsorbed water layer edge to face attraction
is not possible and particles are found relatively distanced separated by
water, and positioned almost in parallel..
Effect on dry strength
Quoting from Ryan & Radford*: =A1=A5Plasticity is one of the properties
affected by the type of cation adsorbed on the clay surface. In a
flocculated clay or body, particles attract one another giving an open
packed particle arrangement requiring much water to produce optimum
plasticity. Such pastes show high yield values and less tendency for
particle alignment under teh application of a stress than do deflocculated
clays or bodies. Flocculation is therefore used to increase the
workability of industrial tableware bodies, although such treatment
suffers from the disadvantage that unfired strength is reduced due to open
particle packing and reduced bulk density. ... dry strength and plasticity
data obtained on bone china bodies prepared were:
Flocculated 19.7 kg cm2 and a Plasticity Index of 0.67
Deflocculated 29.9 kg cm2 and a Plasticity Index of 0.43'
* Whitewwares: Production, Testing & Quality Control. Pergamon Press 1997.
And after that I think we could all do with a break.
Regards,
Andrew
Andrew Sugden on tue 3 feb 04
It would be a bit hectic wouldn't it Wayne. And, whilst it's stretching
the analogy too far, it'll get worse:
Shrinkage ... same number of bicycle messengers in a smaller volume (one
side of the street?)
Firing... gets REALLY hot
Densification ...the messengers are squashed together.
I'll stop now as this is getting silly. Still it would be nice to be able
to watch the reactions & behaviour of the indiviual molecules.
Regards,
Andrew
Jim Murphy on tue 3 feb 04
Hi Andrew & everyone else too,
I'll interject here with the following: IF we DON'T "ignore" the
non-plastics component or shall I say we "covet" them (non-plastics), clay
bodies relying on a house-of-cards microstructure - after firing - may be
designed to have exceptional strength and fracture toughness.
This "strong" house-of-cards microstructure is utilized in some mica
glass-ceramic compositions.
With the right composition, one can have a "plastic" clay body with good
green strength AND superior fired strength due in part to mullite formation
or other controlled crystal growth. There are, of course, many other
'microstructures' that may be formed depending on clay body composition.
There's alot to be learned about glass-ceramic compositions and other
microstructures in the book "Glass-Ceramic Technology" by Wolfram Holand and
George Beall, published 2002 by our own "The American Ceramic Society".
Stronger clay bodies may be developed and with proper control of heatwork,
pyroplastic deformation may be controlled.
Best wishes,
Jim Murphy
on 2/2/04 1:16 PM, Andrew Sugden at andrew.sugden@ORANGE.NET wrote:
<< And in repsonse to Ron's point re. flocculation and the effect on
strength. If we ignore the non-plastics component: a flocculated clay
suspension is likely to have lower packing density than when
deflocculated. Sorry but I'd like to sketch something but the classic
description of 'house of cards' structure of the flocculated state is the
best I can do in text i.e. edge to face arrangements. Poor packing -> more
gaps -> weaker mechanically.>>
Ivor and Olive Lewis on wed 4 feb 04
Hello again Jim Murphy,
Now, do you mean "Covet" as in "eagerly desire" or have you some
onther concept in mind for the appropriation of non clay minerals in a
clay body?
Are you sure the "House of Cards Structure" has exceptional strength
without the intervention of an adhesive matrix? Everytime I tried to
construct one from a pack of cards it would tumble awry and collapse
into a heap unless it was stabilised ! !.
This morning as we travelled north I wrote that plastic clay should be
viewed on three levels. There is the Macro Level where there are
agglomerations of flocs. There is the Micro Level, a conglomeration of
ingredients assemble into flocs. Then there is the molecular level
which deals with physical interactions between material entities. Need
I say this can be engineered into a plausible new concept of clay
plasticity, already well known to material scientists.
Best regards,
Ivor Lewis. Redhill, South Australia
Jim Murphy on wed 4 feb 04
Hi there Ivor,
<without the intervention of an adhesive matrix? Everytime I tried to
construct one from a pack of cards it would tumble awry and collapse
into a heap unless it was stabilised ! !.>>
There are no recipes in the book referenced. However, there are plenty of
SEMs (scanning electron microscopy) images.
The house-of-cards microstructure exists because there are 2 separate phases
('glass' and 'crystalline') in the fired matrix with the combination of
these phases exhibiting greater strength than any single phase could. A SEM
image for fluormica glass-ceramic shows "phase-separated residual
borosilicate glass and affinity of siliceous droplets for mica flakes."
From some of my other "readings", I believe other low-clay (40-50% clay)
bodies have been developed which rely on mullite-needle crystal growth
within a glassy matrix. Some porcelain-stoneware bodies like some used in
porcelain-stoneware floor tiles rely on this type of phase separation.
So, imagine if all of your stacked playing card surrounding surfaces were
enveloped in "glass" and all internal cavities/pockets of your stacked
playing cards were filled by "glass", then the overall strength of your
"house-of-cards" would be increased by many orders of magnitude. In such a
case, the playing cards would be somewhat analogous to the mullite-needle
crystals.
I don't mean to imply either that all porcelain-stoneware bodies are
"plastic". Some 'are' some 'aren't'. I'll say this though, "plasticity" is
not necessarily directly proportional to the amount of clay in a clay body
recipe.
Andrew Sugden has pointed out some very important factors related to
plasticity and mechanical strength, like particle size, CEC, absorbed water
layer thickness, how cations may affect absorbed water layer thickness, etc.
All we need now is some more discussion on the influence of capilliary water
forces on plasticity. Many of the texts just briefly mention these
capilliary forces within page-after-page-after-page of discussion on
charge-theory, etc.
Water, pore-size, capilliary water forces are very important to plasticity.
It doesn't mean that "liquid water" exists in capilliary pores either. Dare
I mention Soil-Mechanics Theory ?
Best wishes,
Jim Murphy
Ron Roy on thu 5 feb 04
I think the confusion in this is due to how much water is present - flocced
bodies - in a slip - are card house type.
In a plastic body - because there is less water between the crystals of
clay - the correct anology is card stack.
At least that is how I am reading the explanation in Hamer.
RR
>> And in repsonse to Ron's point re. flocculation and the effect on
>> strength. If we ignore the non-plastics component: a flocculated clay
>> suspension is likely to have lower packing density than when
>> deflocculated.
>>
>
> This seems to me at least mildly counter-intuitive. I thought that the
>result of flocculation was a drawing together of particles which seems (at
>least at the macro level ) to imply a tigher structure. Could you explain
>more what reduces the packing density ? Perhaps it is related to what you
>describe as a suspension ? What exactly is that in this case ?
>
>Thanx
>Daniel
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on thu 5 feb 04
Hi Andrew,
Read in Lawrence &West on particle arrangement - thay used an electronic
microscope to see them - also Ceramic Masterpieces by Kingery and Vandiver
- many micro photos - very interesting stuff and you don't need a new
wardrobe.
I would bet that a net search will find more of what you want to see.
RR
>Thanks everyone for your comments. For me the recent posts illustarte hwo
>valuable Clayart can be: excahnge of ideas and get the brain cells working.
>
>And in repsonse to Ron's point re. flocculation and the effect on
>strength. If we ignore the non-plastics component: a flocculated clay
>suspension is likely to have lower packing density than when
>deflocculated. Sorry but I'd like to sketch something but the classic
>description of 'house of cards' structure of the flocculated state is the
>best I can do in text i.e. edge to face arrangements. Poor packing -> more
>gaps -> weaker mechanically.
>
>Wouldn't it be great if we could shrink down molecular level and directly
>observe these actions!
>
>Open to comment again....
>
>
>Andrew
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 5 feb 04
Dear Jim,
No quarrel with Soil Mechanics provided the systems being represented
are illustrative of Potters Plastic Clay. I had a thought about the
occurrence and nature of clay in the earths crust. Why are "Mud
Slides" so unexpected and catastrophic? This must happen in
mountainous districts when there has been a period of dry weather and
the soil is parched bone dry. When clay or earth is saturated it
changes to a fluid and the forces which give plastic clay its tenacity
do not seem to form.
It also seems as though comparisons are being made between potters
plastic clay and materials which has been heat processed to cause a
variety of phase and chemical changes. There seems to be a "non
sequitur" embedded in this argument. Why do you need to introduce this
red herring?
And please direct us all to those SEM images of plastic clay at a mag
of X 10,000 or higher. I would dearly love to see them and to know how
they manage to process the subject matter in a vacuum.
Hamer does not mention the glass phase in his illustration. He just
shows images of hexagons in contact with each other. No mention of
water or anything else.
Have you made the Model yet?
Best regards,
Ivor Lewis. Redhill, South Australia
----- Original Message -----
From: "Jim Murphy"
To:
Sent: Thursday, 5 February 2004 4:37
Subject: Re: Designer Clay Bodies
> Hi there Ivor,
>
> <strength
> without the intervention of an adhesive matrix? Everytime I tried
to
> construct one from a pack of cards it would tumble awry and
collapse
> into a heap unless it was stabilised ! !.>>
>
> There are no recipes in the book referenced. However, there are
plenty of
> SEMs (scanning electron microscopy) images.
>
> The house-of-cards microstructure exists because there are 2
separate phases
> ('glass' and 'crystalline') in the fired matrix with the combination
of
> these phases exhibiting greater strength than any single phase
could. A SEM
> image for fluormica glass-ceramic shows "phase-separated residual
> borosilicate glass and affinity of siliceous droplets for mica
flakes."
>
> From some of my other "readings", I believe other low-clay (40-50%
clay)
> bodies have been developed which rely on mullite-needle crystal
growth
> within a glassy matrix. Some porcelain-stoneware bodies like some
used in
> porcelain-stoneware floor tiles rely on this type of phase
separation.
>
> So, imagine if all of your stacked playing card surrounding surfaces
were
> enveloped in "glass" and all internal cavities/pockets of your
stacked
> playing cards were filled by "glass", then the overall strength of
your
> "house-of-cards" would be increased by many orders of magnitude. In
such a
> case, the playing cards would be somewhat analogous to the
mullite-needle
> crystals.
>
> I don't mean to imply either that all porcelain-stoneware bodies are
> "plastic". Some 'are' some 'aren't'. I'll say this though,
"plasticity" is
> not necessarily directly proportional to the amount of clay in a
clay body
> recipe.
>
> Andrew Sugden has pointed out some very important factors related to
> plasticity and mechanical strength, like particle size, CEC,
absorbed water
> layer thickness, how cations may affect absorbed water layer
thickness, etc.
>
> All we need now is some more discussion on the influence of
capilliary water
> forces on plasticity. Many of the texts just briefly mention these
> capilliary forces within page-after-page-after-page of discussion on
> charge-theory, etc.
>
> Water, pore-size, capilliary water forces are very important to
plasticity.
> It doesn't mean that "liquid water" exists in capilliary pores
either. Dare
> I mention Soil-Mechanics Theory ?
>
> Best wishes,
>
> Jim Murphy
>
>
______________________________________________________________________
________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your
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> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Jim Murphy on thu 5 feb 04
Hi Ivor,
<are illustrative of Potters Plastic Clay.>>
<>
Because sometimes bad things happen when the "shear-stress yield point" is
exceeded ? Caused really by permanent shear strain due to plastic flow, or
to put it another way, once it starts, momentum takes over and it ain't
going to stop. As a very wiseman once said, "Don't build your mountain-home
over a running stream".
Here's one for ya, take a small amount of "Potters Plastic Clay" and squeeze
between your thumb and forefinger. Notice upon squeezing, how the clay
rises-up as stress is applied. I believe this rising-up is referred to as
"dilatency" and is due to the mechanical behavior of the clay particles and
water forces - or, if you prefer, "structured-water" forces.
This "dilatency" effect cannot be explained by clay charge-theory alone.
There are clay particles being heaved-up, in part, by "structured water"
forces.
<of X 10,000 or higher. I would dearly love to see them and to know how
they manage to process the subject matter in a vacuum.>>
Hmmm, via a personal email to you, I am sending a jpg image of the mica
glass-ceramic house-of-cards microstructure I referred to. Don't know the
specifics of the method to SEM or TEM - whether they're done in a vacuum or
not. Per Clayart List instructions, I won't clog-up the list with attached
image files though.
<shows images of hexagons in contact with each other. No mention of
water or anything else.>>
I think this was referred to as a "relict" microstructure for mullite
ceramic-glass in Glass-Ceramic Technology. I'll send you a TEM image of that
as well. (Note - I'm talking about fired microstructures here, so, I'm not
sure what your reference to 'water' here means.
> Have you made the Model yet?
I like your magnet & iron filings Plasticity Model and believe it to be
intuitive enough that I have not gathered magnets nor filings to make it
yet. I'll tell you, my friend, as I sit here typing with a patch taped over
my eye, following eye-surgery this morning to remove a Chalazion from my
right upper eyelid, I have no intention of going anywhere near iron filings,
powdered clay, plaster, etc. anytime soon, but I digress.
Now, if one were to squeeze your 'Model', I'd expect if there are enough
filings to coat all magnet surfaces - somewhat similar to water being
absorbed on clay particle surfaces - that "dilatency", or a rising-up, may
too be observed.
All I'm saying is that we shouldn't "de-value" the forces imparted by the
iron filings in your Model, nor the water forces in plastic clay.
Best wishes,
Jim Murphy
Ivor and Olive Lewis on thu 5 feb 04
Dear Andrew Sugden,
You give a summary of what you believe about the nature of Kaolinite
clays, but more recent investigations by the Whiteware Team at Alfred
seem to indicate that your commentary may not be entirely true of pure
mineral Kaolinite.
It is my understanding that your statement about the isomorphous
substitution may be true for Ball Clay. In this condition I believe it
is called "Disordered Kaolinite".
Consider that Kaolin crystals have a positive charge on the outer
surface of the Octahedral plane and a negative charge on the outer
surface of the Tetrahedral plane. This is consonant with the
theoretical picture which emerges if you draw the VESPR model of the
molecular structure of Kaolinite and experimental evidence.
Your statement << The thickness of the adsorbed water layer
thickness is inversely proportional to the electrolyte concentration
of the surrounding water.>> is interesting. Do you mean when the
Electrolyte concentration is Zero the thickness of the structured
water layer is infinite and when the electrolyte concentration is at a
maximum the water layer ceases to exist? Conclusions I draw from this
are that the best plastic clays will be made from waters which contain
no dissolved salts whereas minimal volumes of water loaded with
additives must be used to prepare casting slips and, in addition, wet
weathering of clay would be beneficial to the promotion of high
plasticity and good workability since rain or regular washing would
leach dissolved salts from the raw material.
Would you please describe the structure of Water in your model. I ask
because your description <around the clay particle that has a more regular structure than that
of free water into which it gradually merges >> seem rather vague.
How do the two types of water differ? Can you give us some diagrams?
You seem to be justifying the "Water Hull' model of Lawrence and West
but provide no evidence to support this claim.
Do you know the origins of the "House of Cards" model provided by
Hamer? Is there an original reference to this concept? Although it
seems plausible, have you calculated the spatial relationships between
the clay and water it is supposed to represent? I would like to know
what occupies the "Cubic" spaces within this structure. When I model
this system in my imagination I always finish with spherical empty
voids surrounded by water clinging to the walls created by the clay
crystals. Is this possible?
The "House of Cards" model calls into question your argument about
flocculation where you suggest << Where conditions promote a thin
adsorbed water layer the positive edges of the clay particle may
approach close enough to the negative face to form an electrostatic
bond. >> This seems to be at odds with your earlier claim, with which
I would agree, that the edges of the Kaolin crystals are, to all
intents and purposes, neutral because of the equality of the
electronic nature of the broken valency bonds.
I am pleased to see that more people are joining the discussion and
contributing to this thread.
Thank you for your statement.
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on fri 6 feb 04
Dear Ron Roy,
If Hamer's Dictionary was my sole source of information I would draw
the same conclusion that you give.
It seems plausible and is a logical response.
But I would like to know about the origin of "House of Cards" model.
If it was an observed fact and plastic clay does behave in that way,
who made the observation, when and where was this done and what are
the experimental details. Who informed Frank Hamer of this concept or
is it his invention? Without that knowledge it is no better idea than
any other which might originate in the imagination of another person.
At least yesterday Avril Farley, who called in to see me, had a chance
to handle and play with my Magnetic Model of Plastic Clay. Perhaps you
may like to talk to her about the nature of plastic clay following
that experience. Had not airport security been an issue she would have
taken it away for other people to see.
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on fri 6 feb 04
Dear Ron Roy,
Check out the experimental details for the images you are citing.
Are you sure they were using fully hydrated clays. Or were their
specimens anhydrous.
Details I have of relating to electron microscopes is that the
specimen is held in a vacuum chamber and in many cases the object
examined is a Gold shadowed replica.
Great contributions, keep them coming.
Best regards,
Ivor Lewis. Redhill, South Australia
Bruce Girrell on fri 6 feb 04
Ivor wrote:
> Details I have of relating to electron microscopes is that the
> specimen is held in a vacuum chamber and in many cases the object
> examined is a Gold shadowed replica.
Absolutely correct. And, as we know, the drying of clay distorts its shape
to a significant degree.
There is a technique in microscopy called "critical point drying" (CPD) that
eliminates the surface tension effects during drying (and surface tension
effects are the primary cause of distortion during drying). In the CPD
process temperature and pressure are raised until the fluid in the sample
reaches its critical point, i.e., the point where the density of gas and of
liquid are identical. The pressure is then slowly lowered and what was
liquid leaves the sample as gas without the shrinking effects of surface
tension.
Unfortunately, traditional CPD does not apply well to clay because the water
in a sample first must be exchanged with an intermediate fluid such as
acetone and that process would be difficult due to the very low permeability
of clay. I wrote to a microscopy listserv to which I subscribe and asked
whether the intermediate fluid was essential. Could the process not also be
accomplished without an intermediate fluid as long as the sample itself
could withstand the temperature and pressure needed to reach the critical
point of water? They were intrigued by the thought and suggested that it
would be worthy of publication should I actually take on the project. The
temperature and pressure is high, but not prohibitive, given that I have
access to oilfield equipment that is designed to withstand considerably
higher pressures.
I haven't done it yet, of course, but I am encouraged by the support of the
microscopy community that it would be possible.
Another alternative that has appeared in recent years is the "environmental"
SEM that allows inspection of hydrated samples. The sample cannot be held at
atmospheric pressure though, so there would still be an ongoing drying of
the sample during imaging. Quick work apparently is part of the process.
Bruce "so many projects, so little time" Girrell
Andrew Sugden on fri 6 feb 04
Good evening all,
As I=92ve been bed bound for a few days after pulling a muscle in my back,
whether due to being huddled over a PC reading Clayart or shifting bags of
clay I do not know!!!! Anyway I=92m a little behind with the current posts
but I hope the following will be of interest and continue the discussions,
and, of course, comments are welcomed:
Plasticity
Plasticity has been shown in clay systems that do not contain water. In
the late 1940s Norton found that under vacuum a dry clay constrained by a
rubber membrane exhibited plasticity and behaved in a similar to when
mixed with water.
What is certain is for a liquid & clay system to exhibit plasticity the
liquid must be polar; for example mixing clay with a non-polar liquid such
as paraffin yields a non-plastic mass.
Is water the =91glue=92 holding that holds a body together? Take dry clay &
mix it with water ... a plastic mass can be made ... which can be shaped
and can retain its form. After a prolonged period at 110oC there can be no
water remaining in it yet not only does the article not collapse into a
mass of powder but it also yields its maximum unfired strength.
However the clay mixed with paraffin not only exhibits no plasticity but
also develops no strength.
What is holding a dry clay article together? In addition to the ubiquitous
Van der Waals forces is electrical attraction between the clay particles.
Hence why changing the flocculation state can influence the dry strength -
and plasticity. By mixing with paraffin the charges on the clay particles
resulted in negligible attraction.
However for most whiteware applications water is an essential, and often
overlooked, raw material and I think most potters are happy to consider
that there is something special - perhaps primeval? - about the
interaction between clay and water.
Plasticity compared to ice: whilst not suggested as a model considering
ice may help to appreciate lubrication by water films. Ice itself is not
slippy, this is caused by a thin layer of liquid water across its surface.
Ice that is dry (H2O and not =91dry ice=92 which is frozen CO2) where no
localised melting has occurred has no film and consequently is not slippy.
And Jim=92s comment about Soil Mechanics ... definitely! Since its,
probable, first application to whitewares in the 1950s these concepts have
gathered increasing support. I=92m interested in your thoughts in this area.=
Kaolinite particle shape
Ivor: could you clarify your point regarding your comment =91... true form
used in the real model is Rectangular though Hamer shows Hexagonal
shapes.=92 Am I misunderstanding or are you suggesting kaolinite crystals
are not hexagonal but rectangular in shape?
Magnet model
Whilst not criticising =96 models and demonstrations that we can see and
hold are superb learning tools =96 I am just wondering if this is a little
limited, my thinking being:
A magnet has two poles: N & S
Faces of a kaolinite particle are negative
Edges of a kaolinite particle are amphoteric (containing + & -) and the
attraction forces respective to other particles can be modified by doping.
The N of a magnet will be attracted to the S of another; mixing of a
number in a bag will result in some connected face on face. The faces of
two kaolinite particles will repel each other.
The charges on the edges of kaolinite particles can be changed, and hence
the respective attraction to edges and faces of other particles. This can
not be done with the magnets.
The magnetic flux around a magnet is not representative of the complex
electrical charges across a kaolinite platelet, which can, and do, change
dependent on conditions.
As you say the model can demonstrate water surrounding the clay =96 and
perhaps a single flocculation state. Although drifting from the point it
is noted that slips are not simply deflocculated or flocculated; unlike a
light it=92s not switched on or off. This is easily seen in whiteware slips
as viscosity can range from a static, immobile state to that with a
fluidity approaching water.
House of cards
This description of the arrangements of clay particles in a flocculated
system has been used in many sources, in fact it=92s has something of a
clich=E9, although as with all clich=E9s not without some validity.
Jim: Having had very little experience of glass ceramics I would not
like to comment, although bringing in another discipline is interesting. I
think your suggestion of mullite formation has some merit though I don=92t
think much is likely to be formed in the firing schedules typically used
for most whiteware bodies; whilst growth may start around 1150 to 1300oC I
think prolonged soaks would be needed to get long crystals.
Mullite needles in the mircostructure reminds me of fibre reinforced
composites =96 is this along the lines of your thinking?
I hope you didn=92t misunderstand my suggestion of ignoring, or at least
putting to one side, the non-plastics it=92s just that as clays have such an=
overwhelming influence of the unfired strength that considering them alone
is probably easier.
Certainly non-plastics can have a profound effect on the fired strength of
bodies. Tested tensile strength of ceramics invariably falls considerably
below the theoretical, typically being just 1%. The main reason for this
discrepancy is that the theoretical assumption of mechanical failure is
not wholly valid in application, and one of the weakening mechanisms are
microcracks around relict quartz particles in the fired microstructure.
Having undertaken some work in this area I found that reducing the quartz
content or, more interestingly its particle size, could achieve
significant increases in the fired strength.
And further to your =93...right composition, one can have a "plastic" clay
body with good green strength AND superior fired strength ... Stronger
clay bodies may be developed and with proper control of heatwork,
pyroplastic deformation may be controlled. =93 Amongst the strongest of
whiteware bodies are electrical porcelains which have modulus of rupture
values of greater than 20,000 psi. Not only are these are formulated to
exhibit high plasticity and green strength =96 making them excellent
throwing bodies =96 but must have low pyroplasticity deformation due to the
large size of some insulators which can be up to 4.5 m high and weighing
in the tonnes.
That's it from e tonight.....
Andrew
Ivor and Olive Lewis on sat 7 feb 04
Dear Andrew Sugden,
Glad to hear you are mobile again.
Interesting cogitations:-
<membrane exhibited plasticity and behaved in a similar to when
mixed with water.>> So will ball bearings !!! But only if you have an
elastic boundary to contain the particles.
<the
liquid must be polar; for example mixing clay with a non-polar liquid
such
as paraffin yields a non-plastic mass also develops no strength..>>
Plasticene is a mixture of Oil, wax and Clay. The llubricant and the
vehicle are "Non Polar" but the mixture exhibits plasticity.
<> Yes,
yes, yes !!!!
<which can be shaped and can retain its form. After a prolonged period
at 110oC there can be no water remaining in it yet not only does the
article not collapse into a mass of powder but it also yields its
maximum unfired strength.>> But place it in water and it collapses
<> Water, the final
remnants and residues of salts which act as cement. If you doubt that
water is not the culprit why do people keep their peeps open and bungs
out and doors ajar. If you deny my answer then these actions would not
be necessary. By the way, What makes BlueTack Sticky, what makes Durex
tape sticky
<often overlooked, raw material and I think most potters are happy to
consider that there is something special - perhaps primeval? - about
the
interaction between clay and water.>> There is!! But as you say, in
most of the written comentaries the properties and functions of water
are disregarded.
<considering ice may help to appreciate lubrication by water films. Ice
itself is not slippy, this is caused by a thin layer of liquid water
across its surface. Ice that is dry (H2O and not 'dry ice' which is
frozen CO2) where no localised melting has occurred has no film and
consequently is not slippy.>> Read W. E. Brownell (1976). Forget the
idea of "Lubrication" and adopt the concepts of "Dislocation" and
"Grain Boundary Shear" described by Kingery et al.
<Ivor: could you clarify your point regarding your comment '... true
form
used in the real model is Rectangular though Hamer shows Hexagonal
shapes.' Am I misunderstanding or are you suggesting kaolinite
crystals
are not hexagonal but rectangular in shape?>> No, the "House of
Cards Model" is based on a pack of Playing Cards, Standard Craps or
Stud Pack. Rectangular paste boards. As kids we would build a
structure by laying cards on their edges on the table to make A frame
structures, stabilise them with cards at the sides then add platforms
and so on to get as tall a structure as possible. I do not think this
has been demonstrated as existing in a plastic clay. If you have that
evidence, please supply it so we may be enlightened.
<that we can see and hold are superb learning tools - I am just
wondering if this is a little limited, my thinking being: A magnet
has two poles: N & S.>> True, if they are made that way. Some magnets
have many poles but thre is always equality. You can never have a
solitary magnetic pole. Before you criticise this model I suggest you
go away and build one for yourself. and build a house of cards as
well, to prove how much better it is in representing plasitcity as a
physical condition than my model is.
<> Prof Carty says not.
The face with the hydroxyl elements is Positive (O), the face with the
oxygen atoms (T) is negative. A VESPR analysis of the Basic Molecule
confirms this.
<number in a bag will result in some connected face on face>> YOU ARE
NOT THINKING OF THE TOTAL SYSTEM. Sorry folks. Just had to shout that.
The big problem is that people always forget about the water until
they deflocculate the clay or find it is too sticky
<> Which
model are you using here? If it "House of Cards" look at Hamer's
pictures.
<hence the respective attraction to edges and faces of other particles.
This can not be done with the magnets.>> Only if you disorder the
structure. Wrong about the magnets. It is a simple task to reverse
the polarity of a magnet, or destroy its magnetism.
<complex electrical charges across a kaolinite platelet, which can, and
do, change dependent on conditions.>> True, but we are cosidering a
simple system of the Pure Mineral in Pure Water. Remember, I told you
to buy Isotropic Ferrite Magnets for your model
.
<and perhaps a single flocculation state.>> As you build in more
magnets you get a bigger Floc
<particles in a flocculated system has been used in many sources, in
fact it's has something of a clich=E9, although as with all clich=E9s not
without some validity.>> Yes, it does seem to be a clich=E9. What makes
it a valid fact that the model represents reality?
<don't think much is likely to be formed in the firing schedules
typically used for most whiteware bodies; .>> Mullite is a reaction
product following the pyrolisis of Meta Kaolinite at temperatures
beyond 1000=BAC.
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on sat 7 feb 04
Dear Bruce,
Thanks for confirmation of my thoughts on that one. By the way, I am
now the proud owner of the missing part which connects my camera to my
microscope. All I need now is a freezing stage microtome to get some 5
mu sections on glass !!
Best regards,
Ivor Lewis. Redhill, South Australia
Jim Murphy on sun 8 feb 04
Hello all,
In 'flocced' plastic bodies I look at the arrangement of particles (clay &
other) as being pretty much random, disordered, chaotic even. BUT, a
"plastic" clay BODY, implies there is a balance of clay particles, minerals=
,
non-plastics - whether added by Mother Nature or out-of-the-bag by a
ceramist (Potter, etc.) - and last but not least - WATER !
"Structured-water"? Sure, charge developed on clay particles in water is
related to the differential adsorption of anions and cations from water
molecules. We could go on-and-on debating the "water-hull". Remember though=
,
the net-charge of the overall 'balanced' plastic BODY is Zero (0)!
There's more to "plasticity" than electrical-charge alone.
Kingery, Brownell, etc., they discuss Charge Theory at great length AND the=
y
also mention the opposing Van der Walt and CAPILLIARY WATER FORCES in a
plastic body to help bind things together.
Getting back to "structured-water" for a moment. I think (IMHO) the water i=
s
"MOST" RIGIDLY-structured - some say "ice-like" - "NEAR" the clay particles=
.
When I say, "NEAR", I include both (a) adsorbed water into the clay particl=
e
surface, and (b) ionized water VERY near the clay surfaces where the
charge-strength is also strongest. W.H. East calculated kaolinite surface
water layer thicknesses to be 0.4-0.8 um, so, we're talkin' about very
'thin' water layer thickness. Hey, if the charge-strength gets weaker
farther away from the clay surface, why shouldn't the "rigidity" of the
structured-water be any different ? I don't take that "ice" thing too
literally. =20
Water in a flocced plastic body can 'move', and there are pores/voids for
that water to move into and out of when the clay body is subjected to shear
force.
Soil-Mechanics Theory, as applied to Clay-Water systems is NO panacea, nor
is it anything to be frightened of either. It offers, though, a way of
understanding what's going 'on' with the 'capilliary water forces' mentione=
d
by previous Charge-Theory authors but NOT detailed. Soil-Mechanics helps to
account for that water movement and explain how capilliary water forces hel=
p
to allow plastic behavior.
For an in-depth study on Soil-Mechanics Theory, you may want to read
"Introduction To The Principles Of Ceramic Processing" by J.S. Reed (1988);
also, there's a very well-written 10-page article by George Y. Onoda called
'Mechanism Of Plasticity In Clay-Water Systems' located in the book "Scienc=
e
Of Whitewares".
So then, without going into too great a detail, below I'm listing - in no
particular order - what I believe to be the fundamental nuts-n-bolts to
Soil-Mechanics Theory - as applied to a plastic clay body. Much of what I'v=
e
listed below is derived mainly from George Y. Onoda's article:
1. Frictional Solids - Particles are granular (NOT spherical) masses
which, when
packed together, can move in a percolating network created by void-spac=
e
or
'pores', meaning if you compress one particle into another, the force i=
s
transmitted to other particles due to intimate contact.
2. High Capilliary Pressure - Because of curved menisci, pore water will b=
e
at
a lower pressure than the surrounding atmosphere. This negative
capilliary
pressure creates "suction" providing a means for a "hydrostatic stress"
to
help compress the particle packing. Thus, the effect of the high
negative
capilliary water pressure is the same as the rubber bag in Norton's "dr=
y
clay"
experiment.
3. Opposing Forces - Capilliary water force is said to help pull the
particles
together while the electric charge of clay surfaces keeps them apart.
4. Critical State - Under shear stresses, the body is free to expand due t=
o
dilatancy pressure - particles bumping into one another - until it
(dilatancy
pressure) is countered fully by capilliary pressure. At that point, the
critical state, or plastic state, is achieved. Thereafter, plastic
deformation
occurs freely without volume expansion or contraction.
5. Water Content - In flocculated clay, the loose percolating structure is
highly
compressible, meaning it is capable of being fully saturated over a
range of
water content, while the particles remain interconnected. It is this
feature
which gives flocculated clays a long working range.
6. Water Bleed - The high capilliary pressure and 'fine' pore structure
makes it
very difficult for water to bleed-out. Thus, hydrostatic (pore water)
pressure
is easily sustained even under shear stress conditions.
Again, I believe Soil-Mechanics Theory - as applied to plastic clay bodies =
-
is NOT an 'alternative theory' - but rather, a supplement to Plasticity
Charge Theory. We now have a better understanding of how capilliary pore
water pressure operates to help bind clay particles together.
Andrew also asked about Mullite formation at lower temperature:
<I was not disputing anything about the transformation of kaolinite / meta-
kaolinite / spinel / mullite just wondering how much mullite would be
formed in most whiteware bodies fired to normal schedule.
Certainly the size of the needles formed would not be great =96 longer soaks
would be needed =96 I was thinking about fibre reinforced composites. I
certainly would like to hear more from Jim on this subject.>>
Andrew, while researching 'what was so special about vitrified clay pipe an=
d
some structural clay bodies that allows them to vitrify at lower firing
temperatures (1100-1200 C range)' last year, I discovered that often
illite-rich clays and Shales are used to supply 2:1 sheet silicate minerals
(illite, mica, pyrophyllite, etc.). Of course, these 2:1 silicate minerals
consist of an octahedral Alumina-like sheet sandwiched between two
tetrahedral Silica-like sheets.
Some of these minerals, especially illite, have been found in some research
studies to provide a more fluid-like 'glass' environment during firing in
the temperature range cited, which apparently makes it 'easier' for
mullite-needle crystals to grow - into the more fluid glass - forming a
strong interlocking network in 'glass'. (In principle, not too unlike the
interlocking network in a fiber-reinforced composite I reckon.)
This seems to me to follow the thinking of getting 'better' glass
development - at lower firing temperature - from combined-Silica rather tha=
n
from "free Silica". So, some of these 2:1 minerals appear to be very
beneficial as additions (sometimes in very large amounts recipe-wise) to
clay bodies. Something to think about for those interested in composing
"Designer Clay Bodies".
Andrew, you're right though about the longer length of mullite needles at
higher firing temps (~1300-1400 C). However, even at 1200 C, one study
showed the length of mullite crystals from illite-rich clay (1 um) to be
many times that from a 1:1 kaolinitic clay (100-200 nm). At 1400 C, the
study showed mullite length for illite at >10 um and 0.5 um for kaolinite.
Would it be a stretch-of-the-imagination to suggest that the use of some of
these 2:1 silicate minerals may aid plasticity due, in part, to their two
outer tetrahedral Silica-like sheets ?
Best wishes,
Jim Murphy
Andrew Sugden on sun 8 feb 04
Dear Ivor,
As I think you will agree whilst ClayArt is an excellent forum for debate
it suffers from being text only - no diagrams / photos / demonstrations.
And, if you can excuse the pun things, it would be much easier if the
conversation was fluid: the staccato like question / response / comment
can be slow and difficulty.
Anyway onwards with a few points:
Plasticine
Whilst it=92s certainly plastic =96 hence its name!- the commercial product
does not contain clay, rather it is a mixture of calcium carbonate and
oils & waxes.
Plasticity
From experience I can attest that mixing non-polar liquids with clay
results in a non-plastic mass with little, if any strength. whilst another
polar liquid, glycerol, gives something closer to that when using water.
I would be grateful for of the details about the Kingery reference as the
three books of his I have discuss, at some length, the deformation of
crystals but not movement of the clay-water system.
The rubber membrane/dry clay demonstration is mentioned in =93Ceramic
Fabrication Process=94 which was edited by W.Kingery, and quoting
from =93Under these conditions the thin rubber takes the place of the water
membrane and the dry clay has the same consistency as a clay-water paste=94
Although I admit it is a little lazy (though as I do have five different
bodies to prepare and it is Sunday) to simply quote from others at the end
of this piece are a few I taken from some books on my shelves. Before that
though:
Magnet model
As I stated I was not criticising this as a tool for demonstrations just
noting some limitations.
For example:
Polystyrene balls to represent the non-plastics? The complete lack of
attraction to the iron fillings does not mimic what would occur in a body
where the non-plastics are influenced by the
surrounding water (such as being wetted) and the effect of any flocculants
or deflocculants.
The mass of magnets would be deformed if the iron fillings were not
present. Are you happy that this mirrors the action of clay particles
without any water?
In your magnet model how are you changing polarity or destroying it? To be
like a body system it must be possible to dope the system with a small
amount of something that alters charges and also to dope with something
else to return it to its original state.
How can the magnet model demonstrate a deflocculated state?
Again I=92m not criticising; it is far from a perfect model - not that such
probably exists =96 I simply asking that when it is considered it
limitations be also noted. Which leads on nicely to:
House of cards
This was not suggested as a model of plasticity, a flocculated state or
anything. It is an analogy to help people more easily imagine the
structure of clay particles. As with all analogies extending them will
always lead to their downfall =96 it might as well be asked which particles
are spades and which are clubs. It=92s to help visualise =96 nothing more.
Mullite
I was not disputing anything about the transformation of kaolinite / meta-
kaolinite / spinel / mullite just wondering how much mullite would be
formed in most whiteware bodies fired to normal schedule.
Certainly the size of the needles formed would not be great =96 longer soaks=
would be needed =96 I was thinking about fibre reinforced composites. I
certainly would like to hear more from Jim on this subject.
The transformation is not like the inversions of silica but, in addition
to temperature is time dependent. Other influencing factors include what
the Al and Si containing precursor materials were and other materials
present.
Quotes, with thier source noted first:
Clays: their nature, origin and general properties.
Worrall W.E.
Maclaren & Sons. 1968
As with suspensions, the clay particles in a plastic mass are probably
charged, and carry an adhering layer or film of water molecules, held by
electrostatic forces. Thus, the water present is of two types: (a) =93bound=94=
water, forming films round the clay particles and (b) =93free water=94, in
excess of that required to form films. The thickness of the water films,
as with particles in suspension, depends on the surface density of charge
and on the exchangeable cations present. The available surface area of the
particles is also important, since the amount of =93bound=94 water is greate=
r,
the greater the surface area on which they can be adsorbed. Hence,
plasticity is usually associated with very small particles, i.e. colloidal
particles. Another important factor is the shape of the particles. For a
given mass, a thin platy or fibrous particle possess a greater surface
area than spheres or cubes; therefore the plate-like particles of the clay
minerals tend to have a high surface area, which appears to be conducive
to plasticity.
... Just as two pieces of plate glass can be held together by a film of
water between them, so two platy particles of clay can be made to adhere
by the intervening water films. These water films probably act as
a =93lubricant=94, allowing adjacent particles to glide over one another, an=
d
at the same time, the repulsive forces tend to prevent them approaching
two closely and =93locking=94.
...If the water content of a plastic mass is increased, the clay particles
will be further apart, and the cohesion of the mass is reduced. It has,
therefore, a great tendency to deform under very small applied stresses.
Reducing the water content brings the particles closer together, thus
increasing the rigidity. Thus, a high water content produces a sticky mass
of high yield value and high resistance to flow.
Ceramics: physical and chemical fundamentals.
Salmang H
Butterworths. 1961
=93...the presence of small (less than 2um) charged particles and their
lammelar form are two essential prerequisites of plasticity. Combined they
create the large surface needed for the formation of water films whose
existence makes it possible for the particles to slide over one another =96
the third essential prerequisite of the plastic condition.=94
Industrial Ceramics
Singer F & Singer S.S.
Chapman & Hall. 1963
=93In the plastic clay the water sheaths round the particles and in the
pores play a vital role. Surface tension forces form them into skins which
tend to hold the mass together ... The water between the particles also
acts as a lubricant for their movement, which is assisted by their flaky
structure, softness, rough surface and good cleavage.
Ceramic Science for Materials Technologists
McColm I.J.
Leonard Hill. 1983
=93An ice-like layer of water molecules around the small hexagonal platy
crystals is postulated as the source of clay plasticity. The Water is
believed to be structured in this way because large O- and OH- ions
forming the apices of the tetrahedral sheet and the base of the octahedral
sheet respectively give the particles a negative aspect to surrounding
water since their effectively bury the small Si2_, Mg2+ or Al3+ in the
tetrahedral and octahedral positions within the two-sheet structure. Thus
the ice-like water layer is formed when H+ dipoles on the H2O are
attracted to the particle surface.=94
Now I must go and start mixing those bodies.....
Regards,
Andrew
Jim Murphy on tue 10 feb 04
Oops!
I made a mistake. I had said:
<0.4-0.8 um, so, we're talkin' about very 'thin' water layer thickness.>>
Actually, "East calculated the water film thickness on a kaolinite in the
size range 0.4-0.8 um, at 0.8 nm for H-kaolin, 0.86 nm for Na-kaolin, and
1.06 nm for Ca-kaolin."
So, my original info was completely wrong. The water layer thickness is much
thinner (~ 0.8 - 1 nm) than I mistakenly had indicated previously (0.4-0.8
um).
Regards,
Jim Murphy
Ivor and Olive Lewis on thu 12 feb 04
We can all do it from time to time Jim.
So could that mean only one thousandth part of the water is annexed to
the Clay and the other 99.9% is always free fluid water? If it does,
what are the implications for a plastic clay body given the volumetric
ratios of the various ingredients.
Best regards,
Ivor Lewis. Redhill, South Australia
daniel on thu 12 feb 04
Hi Andrew,
I for one am definitely not tired of it. I have retreated to a safe
distance to watch and hopefully learn. I have insufficient background in
materials and chemistry to follow this at the depth you guys are now
conversing at, so I'm picking up the references and puzzling over the models
for now. I'm keeping and reading the mails, so don't stop on my account.
thanx
D
> Dear Ivor,
>
>
> Before responding to the comments and questions from your last post I
> would like to apologise to anyone else on ClayArt if they think that we
> both are rambling on too much. As a forum perhaps it is inevitable that
> some discussions will drag on but if so to those of you may have tired of
> this long thread I say please excuse us.
>
> Anyway onwards.....
>
> Chapter 14 of Introduction to Ceramics by Kingery ...a 5 minute scan as a
> refresher, before last week I admit to not opening it for couple of years,
> failed to find a single mention of any clay mineral. Rock salt, fluorite
> crystals, alumina, glasses but no clay. Are you suggesting plasticity in
> clay bodies is explained by the phenomena and principles discussed in the
> chapter? According to an earlier post you believed it was due to the
> altered nature of water.
>
> Plasticine
> Having just done a quick web search I found a number of references to clay
> based compositions similar to yours. However my comment in a previous post
> was that calcium carbonate was used with waxes and oils in the commercial
> product. It would seem therefore that its plastic nature is derived from
> the oil and waxes rather than the solid, perhaps the carbonate, or clay in
> the homemade version, is just a filler. Trying to remember back to
> childhood I seem to recall that Plasticine worked considerably better when
> warm, even body temperature. This very narrow temperature sensitivity
> would be consistent with the wax component being significant to its
> plastic character.
>
> Magnetic model
> As written earlier I was not criticising or trying to discourage people
> from build it, just that its limitations should be known. I spent my
> lunchtime in the electronic and instrumentation workshop playing with
> magnets, and ...yes one can get shape change without the iron fillings,
> suggested by you as representing water. Quite why your does not I can not
> say but if you can excuse the playful facetiousness perhaps as I am closer
> to the N pole and you to the S Pole....?
>
> Your description of Worrall?s book as ?simplistic and rather out of date?
> Sure my copy dates back to the 1960s, though the second version was
> published in 1982. However many of the concepts and principles he
> describes are still accepted by researchers, technologists and kaolin
> producers. I myself would hesitate to criticise such a respected authority
> without considerable, and wide ranging, support. And saying it is
> simplistic ... his book is considerably more detailed and sophisticated
> than the magnet model, which, I accept to use your term, was a KISS but
> those in glass houses ....
>
> In response to my question re. changing or destroying the polarity of
> magnets you replied ?Do I need to?? You suggested this approach after I
> asked how the change repulsion and attraction forces resulting from doping
> were being modelled. Remember the nature of the cation and the extent of
> their adsorption profoundly influences properties, and in a flocculated
> body there is edge to face attraction whilst for a deflocculated there is
> repulsion of all faces & edges.
>
> And why should you demonstrate deflocculation in a plastic clay? Because
> it is possible to have a deflocculated plastic body just as it is a
> flocculated one. That clay particles are deflocculated does not preclude
> it from being a solid, plastic mass.
>
> Plate glass & water ... yes quite agree about the role of atmospheric
> pressure. I still think imagining two glass plates helps appreciate the
> sliding of kaolinite particles. And as Dinsdale states ? ... water has two
> effects: it holds the particles together by surface tension forces, but
> when these have been overcome it allows flow to take place easily. The
> flow is much facilitated by the plate-like nature of the particles which
> enables them to move easily with respect to each other.? Quoted from
> Pottery Science: materials, processes and products. Allen Dinsdale. Ellis
> Horwood. 1986.
>
> House of cards
> I can not pass comment on Hamers use, or intention, but in those books I
> have, the people I have discussed the subject with and my own
> understanding this description is just an analogy. It is also in current,
> or at least very recent, use in academic and research fields. For example
> it was used with accompanying sketches in a document published by Ceram
> Research in 2000 called Control of Casting Slips. And Raymond Yong writing
> in the August 2003 issue of, the not so snappily titled, Applied Clay
> Science: International Journal on the Application and Technology of Clays
> and Clay Minerals described clay particles as being in a cardhouse
> structure.
>
> Regarding the references in Singer & Singer, those of Schwartz and Pyle, I
> will request these from the library. And whilst talking about references
> full citations are needed, and is standard practice ... to note ?see
> Carty?s work? or ?Cardew, Brownell, Kingery and other texts? is of very
> little help to those wishing to follow up.
>
> Your note that the magnesium ions mentioned in Ceramic Science for
> Materials Technologist indicated a disordered kaolin (though I think you
> meant kaolinite) ... reference to the book would show that idealised
> crystals of various clays were being described, including chlorite.
>
> And ...?proof by logic not by experiment and observation...? turning this
> back to your earlier comment about the behaviour of water being altered by
> kaolinite ...where is your proof by experiment and observation? And the
> explanation from this must include why other polar liquids also lead to
> plasticity when mixed with kaolinite clays.
>
> I do not think I am alone in reacting when strongly held beliefs are
> challenged. Not that they should not be, in fact by doing so can lead to
> development or in the process of defending them one gains a deeper
> understanding. However when these concepts are well established, and
> continue to be accepted, by many researchers, technologists and kaolin
> producers the burden of evidence must be with the challengers.
>
> I think we are in danger, or probably that point has long passed, of
> rambling off the point. So to confirm my early contention was:
>
> Plasticity of clay. Water is not necessarily needed, this being easily
> proved by experimentation.
>
> Green strength, the presence of water lowers it. A totally dry article is
> stronger than when it was damp. Again this can be demonstrated.
>
> Sliding action of clay particles. Sadly difficult to show but again it is
> widely accepted by many recognised authorities.
>
>
> I still have not had chance to read Jim?s posts so I?ll try later. For now
> to the kiln, it?s glaze firing tonight so fingers crossed for no
> crawling......
>
>
> 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.
Andrew Sugden on thu 12 feb 04
Dear Ivor,
Before responding to the comments and questions from your last post I
would like to apologise to anyone else on ClayArt if they think that we
both are rambling on too much. As a forum perhaps it is inevitable that
some discussions will drag on but if so to those of you may have tired of
this long thread I say please excuse us.
Anyway onwards.....
Chapter 14 of Introduction to Ceramics by Kingery ...a 5 minute scan as a
refresher, before last week I admit to not opening it for couple of years,
failed to find a single mention of any clay mineral. Rock salt, fluorite
crystals, alumina, glasses but no clay. Are you suggesting plasticity in
clay bodies is explained by the phenomena and principles discussed in the
chapter? According to an earlier post you believed it was due to the
altered nature of water.
Plasticine
Having just done a quick web search I found a number of references to clay
based compositions similar to yours. However my comment in a previous post
was that calcium carbonate was used with waxes and oils in the commercial
product. It would seem therefore that its plastic nature is derived from
the oil and waxes rather than the solid, perhaps the carbonate, or clay in
the homemade version, is just a filler. Trying to remember back to
childhood I seem to recall that Plasticine worked considerably better when
warm, even body temperature. This very narrow temperature sensitivity
would be consistent with the wax component being significant to its
plastic character.
Magnetic model
As written earlier I was not criticising or trying to discourage people
from build it, just that its limitations should be known. I spent my
lunchtime in the electronic and instrumentation workshop playing with
magnets, and ...yes one can get shape change without the iron fillings,
suggested by you as representing water. Quite why your does not I can not
say but if you can excuse the playful facetiousness perhaps as I am closer
to the N pole and you to the S Pole....?
Your description of Worrall=92s book as =93simplistic and rather out of date=
=94
Sure my copy dates back to the 1960s, though the second version was
published in 1982. However many of the concepts and principles he
describes are still accepted by researchers, technologists and kaolin
producers. I myself would hesitate to criticise such a respected authority
without considerable, and wide ranging, support. And saying it is
simplistic ... his book is considerably more detailed and sophisticated
than the magnet model, which, I accept to use your term, was a KISS but
those in glass houses ....
In response to my question re. changing or destroying the polarity of
magnets you replied =93Do I need to?=94 You suggested this approach after I
asked how the change repulsion and attraction forces resulting from doping
were being modelled. Remember the nature of the cation and the extent of
their adsorption profoundly influences properties, and in a flocculated
body there is edge to face attraction whilst for a deflocculated there is
repulsion of all faces & edges.
And why should you demonstrate deflocculation in a plastic clay? Because
it is possible to have a deflocculated plastic body just as it is a
flocculated one. That clay particles are deflocculated does not preclude
it from being a solid, plastic mass.
Plate glass & water ... yes quite agree about the role of atmospheric
pressure. I still think imagining two glass plates helps appreciate the
sliding of kaolinite particles. And as Dinsdale states =93 ... water has two=
effects: it holds the particles together by surface tension forces, but
when these have been overcome it allows flow to take place easily. The
flow is much facilitated by the plate-like nature of the particles which
enables them to move easily with respect to each other.=94 Quoted from
Pottery Science: materials, processes and products. Allen Dinsdale. Ellis
Horwood. 1986.
House of cards
I can not pass comment on Hamers use, or intention, but in those books I
have, the people I have discussed the subject with and my own
understanding this description is just an analogy. It is also in current,
or at least very recent, use in academic and research fields. For example
it was used with accompanying sketches in a document published by Ceram
Research in 2000 called Control of Casting Slips. And Raymond Yong writing
in the August 2003 issue of, the not so snappily titled, Applied Clay
Science: International Journal on the Application and Technology of Clays
and Clay Minerals described clay particles as being in a cardhouse
structure.
Regarding the references in Singer & Singer, those of Schwartz and Pyle, I
will request these from the library. And whilst talking about references
full citations are needed, and is standard practice ... to note =93see
Carty=92s work=94 or =93Cardew, Brownell, Kingery and other texts=94 is of v=
ery
little help to those wishing to follow up.
Your note that the magnesium ions mentioned in Ceramic Science for
Materials Technologist indicated a disordered kaolin (though I think you
meant kaolinite) ... reference to the book would show that idealised
crystals of various clays were being described, including chlorite.
And ...=94proof by logic not by experiment and observation...=94 turning thi=
s
back to your earlier comment about the behaviour of water being altered by
kaolinite ...where is your proof by experiment and observation? And the
explanation from this must include why other polar liquids also lead to
plasticity when mixed with kaolinite clays.
I do not think I am alone in reacting when strongly held beliefs are
challenged. Not that they should not be, in fact by doing so can lead to
development or in the process of defending them one gains a deeper
understanding. However when these concepts are well established, and
continue to be accepted, by many researchers, technologists and kaolin
producers the burden of evidence must be with the challengers.
I think we are in danger, or probably that point has long passed, of
rambling off the point. So to confirm my early contention was:
Plasticity of clay. Water is not necessarily needed, this being easily
proved by experimentation.
Green strength, the presence of water lowers it. A totally dry article is
stronger than when it was damp. Again this can be demonstrated.
Sliding action of clay particles. Sadly difficult to show but again it is
widely accepted by many recognised authorities.
I still have not had chance to read Jim=92s posts so I=92ll try later. For n=
ow
to the kiln, it=92s glaze firing tonight so fingers crossed for no
crawling......
Regards,
Andrew
Jim Murphy on thu 12 feb 04
on 2/11/04 9:41 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
<the Clay and the other 99.9% is always free fluid water? If it does,
what are the implications for a plastic clay body given the volumetric
ratios of the various ingredients.>>
Ivor,
The "fish" ain't bitin' today, my friend.
With respect to Lawrence-West's Thermodynamic Theory and Geuy-Freundlich
diffuse-double-layer Theory, Brownell writes, "Upon close examination, it
will be found that both theories are based on the same assumptions and both
only approximate the realities of clay-water systems."
However, there's some interesting plasticity info in 'The Methylene Blue
Index For Whiteware Body Control' article published in the book "Science of
Whitewares".
The above mentioned article discusses East's work measuring structured-water
absorbed on a clay "surface" (thicker water layer for Ca-kaolin than for
Na-kaolin), and Lawrence' work on structured-water surrounding ions in
solution, where he (Lawrence) found as ionic field decreased (0.855 for
Al(+3) to 0.106 for Cs(+1)) the fluidity increased (the viscosity
decreased). Lawrence' work also show Ca(+2) and Al(+3) ions capability of
more tightly binding with water molecules compared to weaker binding due to
the misfit of K(+1) in the water structure.
Funk and Dinger, the authors of 'The Methylene Blue Index For Whiteware Body
Control', go on to conclude, "Combining the structuring of water around an
ion in aqueous solution with the structuring of water adsorbed onto clay
surfaces, and then arguing that flocculating cations further improve the
structure of water already adsorbed onto negative clay surfaces we have a
model for explaining the plastic properties of the clay-water system."
Now, was isn't very clear, is what proportion of the overall
structured-water layer "thickness" is rigid like "ice" and what proportion
is more like fluid-water in Ca(+2) and Na(+1) flocced bodies.
Considering all of the above, including the diffuse-double-layer thickness
from Geuy-Freundlich Theory, some may infer at least two possibilities for
the composition of the "thicker structured-water layer" in a plastic body
flocced by Ca(+2) ions, ('thicker' compared to a thinner overall
structured-water layer in a Na(+1) flocced body): (1) a thicker
substrate-layer depth of more rigid "hard-ice" with approximately the same
depth of fluid-water as in the Na-flocced body; or (2) A thinner and VERY
rigid substrate-layer "hard-ice" component, since the stronger Ca(+2) ions
structure the water molecules through a shorter distance, and with a
relatively thicker depth of more fluid-water.
My own personal "guess" would be (1) above. In hockey-terms, the Gamboni
Machine doesn't need to come out as often!
"Plasticity" perhaps is sustained longer by a thicker substrate layer of ice
with a relatively thin surface water layer.
Just my $0.02.
Best wishes,
Jim Murphy
Ivor and Olive Lewis on thu 12 feb 04
By the way Jim,
How did he arrive at this figure ?
Regards,
Ivor
The Sherman's on fri 13 feb 04
No need to apologize. That is what the delete key is for. Or if one gets
the digest form of ClayArt the scroll function also does the job. There are
topics I'm just not interested in at present but its good to know the
archives are there for future reference. And good titles like this one make
it easy to decide whether or not to read and assist in finding it later.
And trimming the message you are replying to is much appreciated!Talk as
long as you want. That is what the list serve is here for.
Marcey Sherman
Zephyr Pottery
1/2 way out Long Island where the warm temperatures have turned our parking
area to a mud bog that is now freezing into some very interesting shapes.
Andrew wrote:
Subject: Re: Designer Clay Bodies
Dear Ivor,
Before responding to the comments and questions from your last post I
would like to apologise to anyone else on ClayArt if they think that we
both are rambling on too much. As a forum perhaps it is inevitable that
some discussions will drag on but if so to those of you may have tired of
this long thread I say please excuse us.
Anyway onwards.....
Ivor and Olive Lewis on fri 13 feb 04
Dear Michael Wendt,
I seem to recall you were using specimens which were cut square to the
plunger face and that there was no container to restrict lateral flow.
I would not know if your results have meaning in terms of the
characteristic you are considering or not.
Your results do indicate that increasing the water content of a clay
reduces its yield point. But determining if this happens according to
a rule might not be possible from the limited information available.
How it would relate to the strength of a water film I am uncertain.
But the figure of the Surface Tension of Water against Air at 20=BA is
given by Kaye and Laby as 72.75 milli Newtons per Metre, a seemingly
minuscule force in comparison to the pressure you are exerting on your
specimens
However, I would agree with you that plastic clay looses its strength
if it is worked relentlessly while being liberally lubricated with
water.
Best regards,
Ivor Lewis. Redhill, South Australia.
With a forecast of 40=BAC, currently 39=BA C in the shade and five hours
to Sundown. Tomorrow's forecast is 45 =BAC
Ivor and Olive Lewis on fri 13 feb 04
Dear Jim,
Seems a good 00.02c worth to me.
I had a look at the analyses of some typical commercial Kaolins' and
they have very low values for Calcium and much higher for Potassium
and Sodium. Could it be argued that this is a cause of their poor
performance in the plasticity department?
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on fri 13 feb 04
Dear Andrew Sugden,
Perhaps we keep a lot of Lurkers entertained.
If you accept that water close in to clay crystals is behaving as a
solid regardless of who proposed the theory then it seems reasonable
to anticipate that it will deform by Grain Boundary Sliding and the
movement of Lattice Defect Disolcations as described by Kinger and his
collaborators in "Introduction to Ceramics". If this water is solid
but amorphous then Grain Boundary Sliding may be the only source of
motion, regarding clay with its water hull a a grain..
I prefer to consider that this is the principle mode of motion in
clays with high water content and the latter when the clay has less
water Dislocation dominates.
Best regards,
Ivor Lewis. Redhill, South Australia
Paul Herman on fri 13 feb 04
Hello Andrew,
Please continue to ramble. Though I'm not up to participating in this
discussion, it is extremely interesting, and I read every one. I hope
you write an article or book on clay.
No apology is necessary, with the delete key available to all.
You too Ivor, please ramble on!
Thanks and best wishes,
Paul Herman
Great Basin Pottery
Doyle, California US
http://www.greatbasinpottery.com/
----------
>From: Andrew Sugden
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: Designer Clay Bodies
>Date: Thu, Feb 12, 2004, 10:49 AM
>
> Before responding to the comments and questions from your last post I
> would like to apologise to anyone else on ClayArt if they think that we
> both are rambling on too much. As a forum perhaps it is inevitable that
> some discussions will drag on but if so to those of you may have tired of
> this long thread I say please excuse us.
Antoinette Badenhorst on fri 13 feb 04
I am also still on this subject. Just backed off a little to read the
book on potters science. Please keep talking....I'm learning!
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 Ivor and
Olive Lewis
Sent: Thursday, February 12, 2004 10:46 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Designer Clay Bodies
Dear Jim,
Seems a good 00.02c worth to me.
I had a look at the analyses of some typical commercial Kaolins' and
they have very low values for Calcium and much higher for Potassium
and Sodium. Could it be argued that this is a cause of their poor
performance in the plasticity department?
Best regards,
Ivor Lewis. Redhill, South Australia
________________________________________________________________________
______
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.
Jim Murphy on fri 13 feb 04
on 2/12/04 10:45 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
<they have very low values for Calcium and much higher for Potassium
and Sodium. Could it be argued that this is a cause of their poor
performance in the plasticity department?>>
Hi Ivor,
I'm inclined to associate a Kaolin analysis' Calcium value more-so with
content of Whiting, Calcium Carbonate, Chalk, etc.
From Robert Tichane's "Clay Bodies" book, "It is common practice to assume
that the potassium-containing mineral found in English kaolin is a micaceous
material. An important fact to remember is that the mineral equivalent of 1
or 2% potash is 15-30% mica. Thus, this contamination is significant because
it will have a large effect on the softening point of English kaolin
bodies." And, "In general English kaolins have high K2O levels (1.9%) while
American kaolins may have only 0.1-0.2% K2O. So, evaluate Kaolins, in part,
by how much K2O they have for an indication of softening point."
Of course Tichane was commenting on softening point, however, some
literature suggests Mica, as well as some other 2:1 minerals (Illite,
Pyrophyllite, etc.) may influence plasticity though their favorable impact
on Cation Exchange Capacity (CEC), increased charge-strength (thicker, more
rigid structured-water layer ???), etc.
Best wishes,
Jim Murphy
Michael Wendt on fri 13 feb 04
Earlier this week I wanted to see just how much water affects
the yield value of a clay body. My home made test instrument
uses a top plate where the weights are piled connected to a shaft
and a vernier caliper to measure how far a sample has been
crushed down under a known load. The plunger end is exactly
machined to 1 square inch so that the test values represent the
actual force in pounds per square inch required to achieve that
degree of travel. To see the clay tester in action, go to
http://www.wendtpottery.com/claytest.htm
Results: The 310 lb clay batch yielded 0.1295 inches under a load
of 7.85 lbs. After I added 1.5 lbs of water and mixed the batch 5
minutes the yield distance under 7.85 lbs of weight was 0.1410 in.
Astoundingly, after I added 1/2 lb more water and mixed it in the yield
distance increased to 0.2160 inches.
From these figures, is it possible to conclude that the water film value
has a boundary? Below that boundary, yield values from the addition
of water are fairly predictable and linear. Above that boundary value,
the clay body becomes markedly softer with relatively little additional
water.
This ties in nicely with the anecdotal observation that beginners often
overwork pots to the point of collapse by adding ever more water.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
wendtpot@lewiston.com
www.wendtpottery.com
Ivor wrote:
We can all do it from time to time Jim.
So could that mean only one thousandth part of the water is annexed to
the Clay and the other 99.9% is always free fluid water? If it does,
what are the implications for a plastic clay body given the volumetric
ratios of the various ingredients.
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on sat 14 feb 04
Dear Andrew,
Your proposition that magnets without the iron powder can change shape
without the iron fillings being present is true. It also gives rise to
an alternative set of observatons.
How would you interpret your observations (which you have not
described) if we make the assumption that the magnets without iron
powder represent anhydrous Kaolinite, clay without water?
Ivor and Olive Lewis on sat 14 feb 04
Dear Paul Herman,
Glad you enjoy the burbling about clay.
Biggest problem is that the material is so diverse in so many ways
that there are probably no definitive answers.
I smile at some of the things I read.
Not good weather in these part to play with clay at the moment. So I
am making clay and water virtually as a way of learning to work with
a new 3D animation program.
Best regards,
Ivor Lewis. Redhill, South Australia
Michael Wendt on sat 14 feb 04
Dear Ivor,
The test device I am using is intended to mimic as closely as possible the
action of our fingers squeezing a lump of clay to gauge its stiffness. The
main difference is it applies an exact and reproducible amount of force to
the clay over a fixed cross sectional area and then measures the translation
accurately to 1/2 of 1/1000 of an inch. This allows us to duplicate the
yield value in a clay body from batch to batch. I have already tried it on
our clay production line and it works well in holding softness consistent
from batch to batch. It would also allow us to talk to our clay suppliers
about the desired degree of softness we each prefer.
Jon Pacini of Laguna Clay commented earlier that the standard penetrometer
was of little use in formulating clay to the same stiffness batch after
batch. My tests tell why. The measured change in softness as a result of
increasing the amount of water in a batch is non linear and very touchy. He
said the easiest way was to throw with the clay, but that does not help the
end users to communicate their desires to the suppliers.
The device I use is easy to build, costs very little and any potter could
have one for about $30.00 US. As a tool of research into clay behavior, I
can only comment that it is exquisitely sensitive to moisture induced
softness variations and so might serve as a way to study the effectiveness
of various flocculants used to help stiffen flabby clay bodies.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
wendtpot@lewiston.com
www.wendtpottery.com
Ivor wrote:
Dear Michael Wendt,
I seem to recall you were using specimens which were cut square to the
plunger face and that there was no container to restrict lateral flow.
I would not know if your results have meaning in terms of the
characteristic you are considering or not.
Ivor and Olive Lewis on sun 15 feb 04
Dear Michael Wendt,
I think this is a good idea which should be promoted. That you are
getting consistent results is as good a recommendation as is needed
for judging the workability of any clay.
Will you write up the construction and instructions for publication in
PMI so that it is freely and universally available or will you ask
someone to make it under contract
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on sun 15 feb 04
Dear Jim,
No arguments with your summary except to ask about the contrary and
contrasting effects of the Group 1 ions to Group 2 ions during cation
exchange.
Should we predict that natural kaolin deposits with high mica
contamination will tend to become deflocculated when they become
suspensions in water and hence have a much reduced plasticity or
workability in the pasty condition. This seems plausible if Potassium
ions are freely leached from Mica? We aware that this happens to glaze
slops when Sodium ions leach from Nepheline Syenite when it is used as
a fluxing agent in glazes. We also recommend using Calcium Chloride or
Magnesium Sulphate to alleviate the effect.
Are you sure Calcium minerals are components in the mineral
constitution of raw Kaolin. In reply to my inquiry to H. C. Spinks
(April 16 1987) several minerals, including Muscovite and Sericite,
are named but there is no mention of calcium minerals.
We seem to be getting some favourable comments from interested
parties. good that they are joining in. Perhaps they have questions?
Best regards.
Ivor Lewis. Redhill, South Australia
----- Original Message -----
From: "Jim Murphy"
To:
Sent: Saturday, 14 February 2004 4:39
Subject: Re: Designer Clay Bodies
> on 2/12/04 10:45 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU
wrote:
>
> <and
> they have very low values for Calcium and much higher for
Potassium
> and Sodium. Could it be argued that this is a cause of their poor
> performance in the plasticity department?>>
>
> Hi Ivor,
>
> I'm inclined to associate a Kaolin analysis' Calcium value more-so
with
> content of Whiting, Calcium Carbonate, Chalk, etc.
>
> From Robert Tichane's "Clay Bodies" book, "It is common practice to
assume
> that the potassium-containing mineral found in English kaolin is a
micaceous
> material. An important fact to remember is that the mineral
equivalent of 1
> or 2% potash is 15-30% mica. Thus, this contamination is significant
because
> it will have a large effect on the softening point of English kaolin
> bodies." And, "In general English kaolins have high K2O levels
(1.9%) while
> American kaolins may have only 0.1-0.2% K2O. So, evaluate Kaolins,
in part,
> by how much K2O they have for an indication of softening point."
>
> Of course Tichane was commenting on softening point, however, some
> literature suggests Mica, as well as some other 2:1 minerals
(Illite,
> Pyrophyllite, etc.) may influence plasticity though their favorable
impact
> on Cation Exchange Capacity (CEC), increased charge-strength
(thicker, more
> rigid structured-water layer ???), etc.
>
> Best wishes,
>
> Jim Murphy
>
>
______________________________________________________________________
________
> 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.
Jim Murphy on sun 15 feb 04
on 2/14/04 6:47 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
<contamination will tend to become deflocculated when they become
suspensions in water and hence have a much reduced plasticity or
workability in the pasty condition.>>
Hi Ivor,
No ... for this "plastic body" discussion, I wasn't referring to ion
leach/release - in water suspensions - from Mica or other 2:! silicate
"contamination".
In Funk & Dinger's article "The Methylene Blue Index For Whiteware Body
Control", they discuss Grim's 3 'causes' for Cation Exchange Capacity (CEC).
(CEC is NOT only important in deflocculated suspensions though.)
One of these 3 causes is via substitution within the lattice structure
resulting in unbalanced charges. Charges resulting from substitutions in the
octahedral (Alumina) layer would act through a greater distance than charges
due to substitutions in the tetrahedral (Silica) layer. I presume this
"greater distance" is due, in part, to [Si2O5](2-) and [Al2(OH)4](2+)
geometrical/topographical differences.
Charge Theory tells us to associate charge-strength with distance. So, for
equal Specific Surface Area (SSA), a 1:1 kaolinite particle should present a
lower charge strength than a 2:1 illite particle which consists of one
octahedral Alumina layer sandwiched between two tetrahedral Silica layers.
I believe some other authors refer to the substitution process as
"isomorphic substitution". From "Ceramic Processing And Sintering" by M. N.
Rahaman, "In the crystal lattice, some of the cations are replaced by other
cations of lower valence without altering the crystal structure; for
example, Si4+ ions are replaced by Al3+ or Mg2+ ions, and Al3+ ions by Mg2+
ions. This process leads to a deficit of positive charges, which is balanced
by other positive ions (e.g., Na+, K+, or Ca2+) adsorbed on the surface of
the clay particles."
Also from M. N. Rahaman, "The extent of isomorphic substitution is dictated
by the nature of the clay, and this is expressed by the cation exchange
capacity (CEC). The CEC of a clay is the number of charges on the clay that
can be replaced in solution." CEC is important for plastic bodies as well -
where there is "structured-water".
In a "plastic body" then, the case may be made for mixing some CEC-friendly
1:1 clays (Kaolin and/or Ball) together with 2:1 silicate materials (Illite,
Mica, Pyrophyllite) - with their greater charge strength - to help create
and sustain the "structured-water" environment.
This may be important to some with regard to plastic "Designer Clay Bodies".
Best wishes,
Jim Murphy
Andrew Sugden on mon 16 feb 04
Dear All,
Many thanks to Daniel, Marcey, Paul, Antoinette and others who kindly
voiced that contrary to my concerns the recent posts had not drifted away
from being of interest.
Jim & Ivor,
I was very interested in Jim=92s posts, and I think his valuation of $0.02
was underselling himself. Anyway if I could just add, at the current
exchange rate, my =A30.01 worth:
I very much liked the introduction of Soil Mechanics Theory, mainly for
two reasons:
1) Cross fertilisation between disciplines can often pay dividends ...be
it industrial to craft or wider to include say geology and petrology.
2) And on a more personal level I understand that the SM Theory was first
applied to ceramic clay systems by E.C.Bloor in the 1950s. A gentleman who
was an extremely well respected ceramist in the UK industry but was
Technical Manager at Taylor Tunnicliff which merged with Bullers to become
Allied Insulators which is where I first started in ceramics.
Thanks for your summary on SMT, and I=92ll dig out the references you
suggest as a refresher.
Illite & plasticity. The short answer being Yes, yes, yes. The addition of
non-kaolinite minerals as plasticisers is well known, with
montmorillionite being the most well known. And whilst the Illite group
seems a bit of a dust bin group for a number of clay minerals that don=92t
neatly fit in other categories as some ball clays are rich in illinitic
clays their use to increase a bodies plasticity become apparent.
Ca and K in chemical analysis of kaolin.
Obviously oxides in an XRF analysis are indicative of the minerals in the
kaolin but ...
Does the presence of Ca indicate calcium minerals? The answer is a helpful
yes and no. For example kaolins for the English deposits have no free Ca,
and that shown in the chemical analysis is present in the kaolinite
structure having replaced some Al. However other kaolins have both Ca in
the lattice and Ca minerals such as calcite.
Potash .... Robert Tichane was a little off with 1 to 2% indicating 15 to
30% mica. Depending on which grade is being considered the K2O in an
English kaolin is typically 1 to 2.8%, this being contributed by micaceous
minerals, from 4 to no more than 20%, and feldspar, up to 5%. However a
higher K2O certainly indicates a more fluxy clay.
Plasticity model
IMHO I think we may be are getting towards the point of flogging a dead
horse ... plasticity by water film lubrication is the very widely accepted
explanation of the mechanism of plasticity in clay water systems. And
whilst the dislocation of single crystals is discussed in some ceramics
books, though not related to clay plasticity, it has not received any wide
consideration for whitewares.
Considerable work has been done in this area, and on methods of
measurement, in the last 50 years. As far as the latter many have been
suggested which include Compression Plastometer, Pfefferkon, Atterberg,
Yet we are sadly no nearer a definitive one. Although I can not remember
it exactly perhaps it is as well to head the words of an american
researcher, Scott Blair, in the 1940s ...plasticity is like honesty I can
not define it but I know it when I see it. (If anyone has the exact words
and citiation I would be very grateful)
Magnet model
A useful tool to demonstrate how platy particles may organise themselves
and one of a fashion can be moulded. The addition of iron fillings for
water and polystyrene for non-plastics enlarge the model. But it is
simplified, and does not mimic the forces, structures and their changeable
nature. It can not be used to assess or explain actual behaviour.
And if anyone is interested in further rading I woudl strongly recommned,
and sadly I am not on commission the following two
Whitewares: production, testing and quality control
Ryan W and Radford
Pergamon Press. 1987
An Introduction to the Technology of Pottery. 2nd edition
Rado P.
Pergamon Press. 1988
If anyone wants any further information on these, content etc, please
email me.
And back to the casting bench,
Andrew
Ivor and Olive Lewis on tue 17 feb 04
Dear Jim,
I have to admit defeat. Once it goes beyond a simple mixture of clay
and water I loose the plot.
Whatever theorist might say they do not to explain why so much space
is occupied by water and so little space is occupied by clay, in spite
of the opposite being true of their relative masses. Nor do they make
any useful contributions about "Flocs". The nature of Plasticity
resides in those gaps in our knowledge .
Thanks for the discussion. I have no more to contribute.
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on tue 17 feb 04
Dear Andrew Sugden,
I suppose you have to have the last word, at least until I find out on
Friday if the library has been able to get me the Radford and Ryan
text.
But what a pity you do not let us into the secrets of "flocs", if they
do in fact exist in a plastic clay. Or are they just a phenomenon
associated with casting slips?
Best regards and thanks for an enjoyable interlude.
Ivor Lewis. Redhill, South Australia
Andrew Sugden on thu 19 feb 04
Hello Ivor,
Sorry but I didn=92t better explain the ending remark of my last post about
references to the two books. Neither have a great deal about plasticity;
these were suggested as good introductions to whitewares technology.
Ryan & Radford is perhaps as good as a craft potter will currently get if
just a single book is wanted to cover the basics. It is reasonably priced,
easily readable and covers topics from raw materials to body preparation,
making techniques and testing. For example it would be of use for the
recent posts concerning testing for water absorption and plasticity. Being
just 300 pages long only an overview of the topics can be given,
nevertheless it is still a very useful book. The first edition rather than
the reprint is better as the reproduction of photos in the later is not
good. The two authors are former lecturers in Ceramic Technology.
The second book, by Paul Rado who was Research manager at Royal Worcester,
could be considered a companion volume; indeed both were published by The
Institute of Ceramics. Of comparable length to the above similar topics
are covered, though as testing is not a little more detail is given such
as on the structure of kaolinite and a neat introduction to Gouy-
Freundlich=92s double layer theory. Again highly readable and recommended.
Not sure what you meant by the secret of flocs in plastic clay. Consider
two clay slips that are identical other than the flocculation state ... a
deflocculated and a flocculated. The clay particles exist in different
arrangements relative to each other. Both can be dewatered to give a
plastic mass though the filtering characteristics of the two will be
different. The properties of the plastic bodies, and after drying, will
also differ. Particles will experience a range of forces as water is
removed, be it particle to particle charge attraction or repulsion, or
from the suction of a mould or filter or evaporation or .......... After
drying the flocculated body will be mechanically weaker.
The clay structure of the two slips will change on drying, the house of
cards arrangement of the flocculated, will gradually change, collapse, but
it will not match that of the deflocculated. If the bodes are mixed again
with water of the same chemistry, say deionised, the differential
characteristics of the respective parent slips will be recovered without
any fresh doping.
Of course it gets more complicated when you consider that the majority of
kaolinite particles exist as stacks rather than nice, neat, single little
hexagons plus the kaolin could contain other clay minerals, albeit in
relatively small amounts. And then ball clays have higher amounts of non-
kaolinite including illites, mica, sericite.... thinking about all this,
trying to understand it could be the way to the funny farm!!!!
Regards,
Andrew
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