Cynthia Haviland on fri 8 sep 06
Hi all,=20
Am interested on having some thixtropic clay included in a demo next =
Thurs on clay types and properties. The demo is next Thurs. Anyone? =
Thanks.=20
Cynthia=20
Down to Earth Pottery, VT
Ron Roy on fri 8 sep 06
Hi Cynthia,
Adding a source of soluble sodium will do it - just dissolve some soda ash
in some water - slice some thin sheets of clay and add a drop of the
solution and mix by hand till it becomes soft - keep track of the weight of
the clay and how many drops of solution and you can do as much as you want.
You will need to dry the clay out after defloccing it to get it back to
working consistency.
If you keep it in the wet deflocced state you can reverse to flocculated by
adding some solution of Epsom salts.
Trick it to only use as much deflocculer as is needed.
Not all clay will deflocc with time by the way - soluble alkalies are the
most likely cause - without them the natural progression is to better
flocculation due to bacterial influence - aged clay works better - is
better flocculated - if there are no defloccing solubles present.
RR
>Hi all,
>
>Am interested on having some thixtropic clay included in a demo next Thurs
>on clay types and properties. The demo is next Thurs. Anyone? Thanks.
>
>Cynthia
>Down to Earth Pottery, VT
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Bruce Girrell on fri 8 sep 06
Cynthia Haviland
> Am interested on having some thixtropic clay included in a demo
> next Thurs on clay types and properties.
For all practical purposes, _all_ clays are thixotropic. What are you trying
to demonstrate?
All you need is a log of clay that has been sitting around for a while, say,
a couple of months or more. Have people feel how stiff it is. Now drop it on
the floor several times from different angles. Have them feel it again. Big
difference. Thixotropy.
Bruce "and the word of the day is..." Girrell
Lee Love on fri 8 sep 06
from the archives:
Listed are both Cone 5 and Cone 9 clay bodies:
^5 ^9 '
25 25 Kentucky Ball Clay
15 15 Spodumene
15 15 Kona F-4
15 15 Kaolin (EPK)
10 25 Flint (silica)
20 5 Ferro Frit #3110
Also listed is a glaze for thixotropic clay body:
(Cone 5, crazes at Cone 9)
16 Kaolin (EPK)
24 Nepheline Syenite
60 Fetto Frit #3124
The book explains how to manipulate the clay - kind of pulling and shaking
it
at the same time - with pictures. Probably a good idea to get the book. ( I
found a copy at a used book store....)
If you get around to creating this stuff and working with it, hope you
let us know how it turns out. I'd love to hear about it!
Here is a recipe for Silly Puddy (is it *Thixtropic?)*
Materials:
* Large flask of 55% Elmer's glue solution in water * Large flask of 16%
sodium borate * Small styrofoam or Dixie cups * Wooden stir sticks * Food
coloring * Zip lock bags
Procedure: The Elmer's glue solution and the sodium borate are mixed in a
4:1 ratio. The procedure can be followed from the slime procedure above.
--
Lee in Mashiko, Japan
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
John Britt on fri 8 sep 06
Hello all,
I have a recipe for thixotropic material (not necessarily clay). I found
it when making cones and I misread the recipe (left out the clay).
It is a great example of thixotropic material.
83.5 g. Custer Feldspar
35.0 g. Whiting
180.0 g. Silica
It does not add to 100 % because it is not a real recipe. You can retotal
for yourself if you like. I just make up that amount and it is about right
to hold in your hand and squeeze (becomes very hard) or to shake (starts
to flow incredibly). It is a great teaching aid.
Hope it helps,
John Britt
www.johnbrittpottery.com
Vince Pitelka on fri 8 sep 06
> All you need is a log of clay that has been sitting around for a while,
> say,
> a couple of months or more. Have people feel how stiff it is. Now drop it
> on
> the floor several times from different angles. Have them feel it again.
> Big
> difference. Thixotropy.
Bruce -
Sorry, but that's not the case at all. All clay "settles" over time, as the
particles come more directly in contact with one another, displacing the
water layers. That makes the mass seem stiff and un-plastic. When you drop
the clay on the floor a few times, it mobilizes the particles,
re-distributing the water layers, restoring plasticity. That has nothing at
all to do with thixotropy, which is most often connected to deflocculation
caused by soluble alkalies. A thixotropic claybody seems stiff, but when
manipulated, it turns to a semi-liquid mass that can be stretched like taffy
and will not stand up in a structural sense unless it is left alone and
allowed to stabilize. That's very different from the simple re-mobilization
of a "settled" mass of regular clay.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Lynne and Bruce Girrell on sat 9 sep 06
Vince,
I beg to differ. Thixotropy is increased fluidity as a result of mechanical
disturbance, particularly shearing forces. If deflocculated clays exhibit
this property to a greater degree, that's fine. But normal clays are
thixotropic, too.
And I seriously have to question this assertion:
> All clay "settles" over time, as the particles come more directly
> in contact with one another, displacing the water layers.
Sounds good, but if the clay is settling, displacing the water, where does
the water go? And how does it suddenly reappear between the tightly adhering
clay platelets when the clay is moved?
Bruce Girrell
Vince Pitelka on sat 9 sep 06
> I beg to differ. Thixotropy is increased fluidity as a result of
> mechanical
> disturbance, particularly shearing forces. If deflocculated clays exhibit
> this property to a greater degree, that's fine. But normal clays are
> thixotropic, too.
Bruce -
That still does not correspond to what I understand, and I do not see how
you can say that normal clays are thixotropic. They, are not, in any sense
of the word. Thixotropy seems to be primarily a quality of gels that will
semi or completely solidify when left alone, and then liquify when agitated.
Normal clay does not do anything like that. If it has been sitting for a
long time it gets stiffer, for the reasons that I explained, and then when
mobilized, it returns to a plastic state, but it does not approach anything
like liquification unless it has become deflocculated through dissolution of
alkalis into the water of plasticity. Deflocculated clay of a certain
consistency can be very gel-like, and behaves with true thixotropy,
semi-solidifying or holding it's shape almost as soon as movement or
agitation stops.
To reiterate, normal clays with a neutral or slightly acidic chemistry are
not thixotropic, and do not behave in such a way that could be called
thixotropic. Clays that have an alkaline chemistry (deflocculated clays)
can be thixotropic, because of the gel-like consistency and behavior.
I do not claim to be an expert on this, but I am certainly not about to
accept the statement that "all clays are thixotropic," unless you can
explain to me how that could be possible. I think I understand the concept
of thixotropy, and it simply does not apply to normal plastic clay.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Ivor and Olive Lewis on sun 10 sep 06
Dear Ron Roy,,
You are confusing my understanding of the behaviour of clay.
As I was given to understand many years ago, thixotropic substances were =
generally solid in nature but when agitated or subject to mechanical =
stress they tended to become fluid. Thixotropic was particularly applied =
to household paints that remained solid in the can until stirred by the =
brush. Once the agitation stopped they immediately solidified again on =
the bristles of the brush. When paint was applied to the wall or ceiling =
it fluidised and flowed to give a good smooth textureless surface =
without running or dripping.
Are you saying that adding a deflocculant to a clay will allow this to =
happen ? Another thing, are those bags of hard solid clay that I drop on =
the floor to soften them actually in the deflocculated and not the =
flocculated state ? I ask this because I thought the fact that they =
softened indicated that the clay was thixotropic. But from what you say, =
this must be incorrect because they have no added alkali.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
John Hesselberth on sun 10 sep 06
On Sep 9, 2006, at 9:26 PM, Vince Pitelka wrote:
> I do not claim to be an expert on this, but I am certainly not
> about to
> accept the statement that "all clays are thixotropic," unless you can
> explain to me how that could be possible. I think I understand the
> concept
> of thixotropy, and it simply does not apply to normal plastic clay.
> - Vince
Vince, I don't think you understand the definition of thixotropic.
You are being too black and white about it. The term simply applies
to materials which become less viscous when subjected to an applied
stress. There are all degrees of thixotropic behavior. You are used
to thinking it is a very dramatic change in viscosity, but it can be
a very tiny one. And the underlying cause is not specified in the
definition of the word. If the material "shear thins" or becomes less
viscous under applied stress it is thixotropic.
Regards,
John
Vince Pitelka on sun 10 sep 06
> So, I know the geologists call it liquifaction, whether it's clay or sand,
> but is this also an example of thixotropy?
Linda -
Yes, it's an excellent example, and certainly one of the most disturbing
examples of thixotropy. I remember from geology classes at Merritt College
in Oakland in the 60s, when they told us about bay fill land turnning to a
bowl-full-of-jello in an earthquake. No structure can withstand that.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Vince Pitelka on sun 10 sep 06
Bruce -
I am learning things I did not know about thixotropy. I can see how there
are relative degrees of thixotropy, and that one could interpret the word to
imply that many clays are thixotropic to some degree. I am still not
comfortable with the statement that all clays are thixotropic, because they
are not. Freshly-mixed clay does not behave in a thixotropic fashion in any
way. Clay has to sit and settle for a long time before anything resembling
thixotropy comes into play, or else it has to be deflocculated, so that
there is a repulsion force acting between particles.
Regarding the water layers, it's really pretty simple. When clay has been
sitting over time, the water is still there distributed throughout, but
gravity causes the the particles to re-orient so that there are multiple
contact points between particles, creating friction, which causes the clay
to seem stiff. The particles are not really moving closer together except
at the contact points, and there is still plenty of room for the water. The
water is not displaced from the clay mass, it is simply redistributed
locally, and is no longer distributed in even lubricating layers between the
particles. After the clay has been sitting for an extended period of time,
assuming that no water has evaporated from the clay, remobilizing through
dropping on the floor or other wedging processes simply restores the even
water layers lubricating the particles, and the clay exhibits the expected
plastic qualities.
Part of my reaction to this discussion is that for the last 40 years the
studio clay world has used the term "thixotropic clay" to refer to
claybodies that exhibit extreme and obvious thixotropy. So, you might be
technically correct in stretching the application of the term to say that
many clays exhibit some degree of thixotropy, but what have you
accomplished? To say that all clay is thixotropic simply muddies the waters
and confuses people. As I see it, clay that is recently mixed exhibits no
thixotropy at all. Clay that has been sitting for a long period of time and
is then remobilized exhibits behavior that could be called thixotropy,
although it is only in the remobilization that any thixotropy is apparent.
Once it is remobilized there is no thixotropic behavior at all unless it is
once again left to sit for a long period of time. Clay that has an
appropriate moisture content and is deflocculated can exhibit extreme
thixotropic behavior, where it seems to "set up" almost immediately when
left undisturbed, and seems to turn jelly-like as soon as it is agitated.
The latter is what has traditionally been referred to as thixotropic clay.
An excellent example of unexpected thixotropy can happen with a porcelain or
whiteware body is fluxed with soda feldspar or neph sy. As you know, over
time those fluxes can release soluble sodium into the water of plasticity,
deflocculating the clay and making it behave extremely thixotropic.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
William & Susan Schran User on sun 10 sep 06
On 9/10/06 8:02 AM, "John Hesselberth" wrote:
> The term simply applies
> to materials which become less viscous when subjected to an applied
> stress. There are all degrees of thixotropic behavior. You are used
> to thinking it is a very dramatic change in viscosity, but it can be
> a very tiny one. And the underlying cause is not specified in the
> definition of the word.
I recall reading about thixotropic clay in Ceramics Monthly many years ago
while in school and mixing up a batch.
With the clay that I mixed, there was a dramatic change in the consistency
when at rest and then agitated.
When agitated/disturbed the clay became runny, much like hot lava, requiring
a mold to support a desired shape. Yet when allowed to rest, undisturbed, it
retained the shape as a "normal" moist clay, but also retaining the surface
as it was in the "wet" state.
Here's some examples:
http://www.claytonbailey.com/blob.htm
http://www.worsleyschool.net/science/files/thixotropic/materials.html
And a related study of clay bodies:
http://www.ceramicindustry.com/CDA/Articles/Feature_Article/fcd8eaeeba25d010
VgnVCM100000f932a8c0____
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Linda - Pacifica on sun 10 sep 06
You are reminding me of when I first arrived in San Francisco and was working in a lab at SF General Hospital. Another tech was performing a test done in a bed of suspended resin particles to which a test sample and then current is applied.
She showed me the bed of resin, which looked like a bed of dryish sand, like you see at the shore. Then one of the docs came over and gave the bed of resin a sharp lateral knock. It turned to a liquid, jellyish mass and he declared: "That's liquifaction and that's what will happen to all the bay mud when the big one comes." Scared me silly and I vowed to never live on bay mud.
Of course that bay mud is clay with lots of organics suspended in water, more or less water at various times of the year.
So, I know the geologists call it liquifaction, whether it's clay or sand, but is this also an example of thixotropy?
Linda
in Pacifica on what passes for rocky ledge in this earthquake zone.
On Sunday, September 10, 2006, at 07:26AM, William & Susan Schran User wrote:
>On 9/10/06 8:02 AM, "John Hesselberth" wrote:
>
>> The term simply applies
>> to materials which become less viscous when subjected to an applied
>> stress. There are all degrees of thixotropic behavior. You are used
>> to thinking it is a very dramatic change in viscosity, but it can be
>> a very tiny one. And the underlying cause is not specified in the
>> definition of the word.
>
>I recall reading about thixotropic clay in Ceramics Monthly many years ago
>while in school and mixing up a batch.
>
>With the clay that I mixed, there was a dramatic change in the consistency
>when at rest and then agitated.
>
>When agitated/disturbed the clay became runny, much like hot lava, requiring
>a mold to support a desired shape. Yet when allowed to rest, undisturbed, it
>retained the shape as a "normal" moist clay, but also retaining the surface
>as it was in the "wet" state.
>
>Here's some examples:
>
>http://www.claytonbailey.com/blob.htm
>
>http://www.worsleyschool.net/science/files/thixotropic/materials.html
>
>And a related study of clay bodies:
>
>http://www.ceramicindustry.com/CDA/Articles/Feature_Article/fcd8eaeeba25d010
>VgnVCM100000f932a8c0____
>
>
>-- William "Bill" Schran
> Fredericksburg, Virginia
> wschran@cox.net
> wschran@nvcc.edu
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
>
Ron Roy on sun 10 sep 06
Hi Ivor,
Yes - when you drop a hard lump of wet clay and it goes soft - then the
clay is deflocculated to some extent. It must mean that some materials in
the body are releasing something that is deflocking the body.
Some materials release sodium into clay - it may take weeks or months - and
that would cause the deflocculation - an example of such a material would
be Neph Sy.
Some clays - notable in Alberta in Canada - have natural occurring alkalies
in them - those clays exhibit the same problems when incorporated into clay
bodies.
I can remember a potter from Alberta saying to me - when he saw some of my
pots in a traveling show - that he thought it was impossible to throw
anything that big - because he was working with partially deflocculated
clay.
I have direct experience here - when Buckingham Spar was no longer produced
- and I was using it as a body flux - I replaced it with Neph Sy. The clay
was impossible to work with in a very short time. When I switched to G200
spar the problem disappeared.
When clay bodies age naturally - and no soluble alkalies are present - they
become more flocculated - through bacterial action.
One way of counteracting the deflocculation of a clay body (or glaze) is to
add a small amount of dissolved Epsom Salts when mixing - this will counter
any tendency of the clay to deflock.
RR
>You are confusing my understanding of the behaviour of clay.
>
>As I was given to understand many years ago, thixotropic substances were
>generally solid in nature but when agitated or subject to mechanical
>stress they tended to become fluid. Thixotropic was particularly applied
>to household paints that remained solid in the can until stirred by the
>brush. Once the agitation stopped they immediately solidified again on the
>bristles of the brush. When paint was applied to the wall or ceiling it
>fluidised and flowed to give a good smooth textureless surface without
>running or dripping.
>
>Are you saying that adding a deflocculant to a clay will allow this to
>happen ? Another thing, are those bags of hard solid clay that I drop on
>the floor to soften them actually in the deflocculated and not the
>flocculated state ? I ask this because I thought the fact that they
>softened indicated that the clay was thixotropic. But from what you say,
>this must be incorrect because they have no added alkali.
>
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Edouard Bastarache Inc. on sun 10 sep 06
Hello Vince,
one exemple of thixotropic clay is the state in
which
the underlying clay is before a lanslide.
Our province and region are prone to these.
A whole village was engulfed by the Saguenay River
at the beginning of the 70s. A small earthquaque
occurred
before and the clay that was thixotropic became
fluid and
most of the village went down the river. Many
escaped
and were relocated but, 37 died.
Also, if you mix clays by the slurry method you
find
clays that appear to become thicker with the
removal/
evaporation of water; then you stir with a stick
and it
becomes very fluid again.
Later,
Edouard Bastarache
Le Français Volant
The Flying Frenchman
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.pshcanada.com/Toxicology.htm
http://www.flickr.com/photos/30058682@N00/
http://thepottersshop.blogspot.com/
----- Original Message -----
From: "Vince Pitelka"
To:
Sent: Saturday, September 09, 2006 9:26 PM
Subject: Re: Thixtropic clay
>> I beg to differ. Thixotropy is increased
>> fluidity as a result of
>> mechanical
>> disturbance, particularly shearing forces. If
>> deflocculated clays exhibit
>> this property to a greater degree, that's fine.
>> But normal clays are
>> thixotropic, too.
>
> Bruce -
> That still does not correspond to what I
> understand, and I do not see how
> you can say that normal clays are thixotropic.
> They, are not, in any sense
> of the word. Thixotropy seems to be primarily a
> quality of gels that will
> semi or completely solidify when left alone, and
> then liquify when agitated.
> Normal clay does not do anything like that. If
> it has been sitting for a
> long time it gets stiffer, for the reasons that
> I explained, and then when
> mobilized, it returns to a plastic state, but it
> does not approach anything
> like liquification unless it has become
> deflocculated through dissolution of
> alkalis into the water of plasticity.
> Deflocculated clay of a certain
> consistency can be very gel-like, and behaves
> with true thixotropy,
> semi-solidifying or holding it's shape almost as
> soon as movement or
> agitation stops.
>
> To reiterate, normal clays with a neutral or
> slightly acidic chemistry are
> not thixotropic, and do not behave in such a way
> that could be called
> thixotropic. Clays that have an alkaline
> chemistry (deflocculated clays)
> can be thixotropic, because of the gel-like
> consistency and behavior.
>
> I do not claim to be an expert on this, but I am
> certainly not about to
> accept the statement that "all clays are
> thixotropic," unless you can
> explain to me how that could be possible. I
> think I understand the concept
> of thixotropy, and it simply does not apply to
> normal plastic clay.
> - Vince
>
> Vince Pitelka
> Appalachian Center for Craft, Tennessee
> Technological University
> Smithville TN 37166, 615/597-6801 x111
> vpitelka@dtccom.net, wpitelka@tntech.edu
> http://iweb.tntech.edu/wpitelka/
> http://www.tntech.edu/craftcenter/
>
> ______________________________________________________________________________
> 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.
>
Lynne and Bruce Girrell on sun 10 sep 06
Vince wrote:
> ... I do not see how you can say that normal clays are thixotropic.
Well, before going further with this discussion, it appears that we need to
get clear on what each of us means by "thixotropic."
If we want to stick with the strict definition of thixtropy/thixotropic,
then we are speaking about gels only. If this is the case, then I would
think that we would be talking more about suspensions of bentonite and the
like instead of formable clays. But if this is the case, then I have
completely misunderstood the subject of the discussion and I withdraw my
comments. Remember, I did ask what it was that the original poster was
trying to demonstrate.
On the other hand, the context of the discussion appears to me to indicate
that we are using thixotropic in a more general sense, applying the word to
plastic mixtures of clay and water (and potentially other additives). In
this case we are discussing "materials that exhibit decreased viscosity when
mechanically disturbed." Please feel free to provide your own words to help
clarify the meaning.
In this case, the fact that clay stiffens up as it sits undisturbed and gets
noticeably softer when worked is sufficient to call it thixotropic.
You state:
> If [normal clay] has been sitting for a long time it gets stiffer,
> for the reasons that I explained, and then when
> mobilized, it returns to a plastic state,
You provided a reason, but I expressed great reservation about your
explanation. Reiterating the statement does not make it any more valid. I do
not see how your concept of migration of the water molcules would stand up
to close examination.
Your description of the clay particles moving closer together would be
analogous to glaze settling in a bucket when left unused for a period of
time. Indeed, the particulate portion of a settled glaze does become more
viscous and when mixed up again it becomes less viscous. But I see two
problems with this explanation:
1) When considering the movement of clay particulates toward one another you
must also consider the consequences of that motion. Just as the undisturbed
glaze bucket develops a water layer at the surface as the particulate mass
agglomerates, clay particles clustering closer together in an undisturbed
hunk of clay would also leave a larger space for the water molecules to
accumulate in. Unlike the glaze bucket though, there would not be a separate
water layer and particulate layer, but rather there would be volumes that
are "more clay" and volumes that are "more water". Given this model, I could
make an argument for _decreased_ viscosity as the water migration occurs, as
the mixture would start acting more like a sand/water combination than a
clay/water combination. The larger globs of water between the clay particles
(larger than when the clay has been recently worked) would provide
_increased_ fluidity.
2) What happens when the clay is disturbed? Remember that we already agree
that it takes no more than dropping the clay a few times to make it feel
dramatically softer. The clay does not have to be wedged, pugged, or
otherwise strongly worked to regain its more fluid state. How could your
water migration explanation account for this? The water, which was
originally between clay particles has been displaced. In order for the
original plasticity of the clay to reappear, the water would have to make
its way back between the clay particles. If the forces between clay
particles were strong enough to displace the water in the first place, it
would be very difficult for the water to displace the clay particles and
take up its place again to provide the fluidity. While you could make an
argument for this happening during wedging, such measures are not required
to restore the fluidity of the clay as already noted; all we have to do is
slam it a few times.
You state:
> ... I am certainly not about to accept the statement that "all clays are
thixotropic,"
> unless you can explain to me how that could be possible.
Fair enough.
I think we are all on the same page when I say that we are dealing with a
system involving charged particles - clay platelets, water molecules, and
the ions that you introduce with deflocculants all carry an electrical
charge. When left to sit undisturbed for some time, the electrical forces
between these various constituents will tend to create weak bonds between
them. Nothing gets displaced to any great degree, they just tend to line up
with each other.
An analogy would be a set of magnets on pivots, close enough to one another
to be influenced by the other's field, yet restricted so that they can't
actually touch. If you "work" them, by spinning one or both and then allow
them to settle they will, after a time, end up aligning with one another.
Electrical charges work in a similar way.
So after these alignments have set up, it takes some energy to disrupt them.
Hence, the clay feels stiffer. Slam the clay a couple of times and enough
displacement occurs to disrupt the alignments. Suddenly the clay is softer.
The water hasn't gone anywhere. The clay particles haven't gone anywhere.
Thus, the clay mass almost instantly regains its original plasticity.
What about your deflocculants? All you are doing is throwing a particular
type of charged particles into the mix, allowing the effect, as I have
described it, to be accentuated. Therefore, you observe a stronger
thixotropy effect in such mixtures.
To summarize:
1) Are we strictly speaking of gels or not?
2) I feel that your water migration explanation does not adequately explain
the observed behavior of clay and I ask you to substantiate your model
3) I feel that I provide an explanation that does adequately explain the
observed behavior of clay.
Bruce "your court" Girrell
Ivor and Olive Lewis on mon 11 sep 06
Glen Nelson in the fourth edition of "Ceramics. A Potter's Handbook" =
introduced the concept of Thixotropic clay, as an artistic medium, to =
the world . He gives two recipes and explains how to achieve clay in the =
required condition. But neither recipe contains ingredients that might =
induce the necessary degree of deflocculation. His instructions propose =
large amounts of deflocculant should be added and the mixture aged for a =
long time.=20
To add more information, Robert Fournier defines Thixotropy, confirms =
the need to apply large quantities of deflocculant
It is clear that time is of the essence and that the longer these "Non =
Newtonian" fluids remain undisturbed the greater their viscosity. Our =
current discussion makes it clear that once a clay has been converted =
into a thixotropic medium it no longer exhibits the quality of =
Plasticity.
Another question whose answer might throw some light on observations =
about plastic bodies in the bag gaining increased workability after =
being dropped on the floor would be some notes on their compositions. I =
have always thought, and continue to think, this change happens because =
large proportions of Bentonite are added to mixtures that are composed =
of relatively large quantities of non plastic constituents and coarser =
clay such as Kaolin or where Ball Clay is avoided to eliminate loss of =
translucency and discolouration. The structural differences between the =
Kaolin (T-O) group of clays and Montmorillonite (T-O-T) minerals has a =
profound effect on their electronic behaviour, enhancing the degree of =
deflocculation.
So it seems to me that a good Thixotropic clay will be well =
deflocculated and have a minimum amount of water, consistent with =
creating a stiff, fluid, material.
I hope I have managed to introduce a few new ideas and not re-iterate =
those already proposed.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
earlk on mon 11 sep 06
I've seen lots of theories postulated in this
thread but not really much in terms of hard
facts so I feel free to throw out my own pet
hypothesis.
When studying chemistry, especially organic
chemistry, one learns about hydrogen bonds.
Hydrogen bonds are quite weak in comparison
to covalent or ionic bonds that hold atoms
together into molecules. Typically hydrogen
bonds develop between two molecules when
there is a slight charge separation such that
the two molecules attract each other due to
opposite electrical charge forces. Although
each hydrogen bond is relativily weak a large
number of them can create a quite strong
attraction force between two, or more, molecules.
It is my hypothesis that clay can, over time,
develop a large number of hydrogen bonds
between adjacent particles thereby making
the clay stiff. When one drops a bag of clay
onto a hard surface there is sufficient shear
force generated between the particles to
disrupt these hydrogen bonds. Once the
bonds are broken the clay particles are free
to slide past each other resulting in the clay
feeling softer.
At least this sounds as good as any other
hypothesis put forward so far.
earlk...
bothell, wa, usa
but not much longer
John Hesselberth on mon 11 sep 06
On Sep 10, 2006, at 8:45 PM, Vince Pitelka wrote:
> Part of my reaction to this discussion is that for the last 40
> years the
> studio clay world has used the term "thixotropic clay" to refer to
> claybodies that exhibit extreme and obvious thixotropy.
Hi Vince,
I agree that this happens. The meanings of words often evolve with
different subtleties in different disciplines. You may remember a
discussion on the meaning of dunting a few months ago. Apparently in
the manufacturing end of ceramics dunting breaks are due to too rapid
heating or cooling whereas studio potters have expanded the
definition to include breaks caused by stress buildup from glaze/clay
mismatch that may occur after the piece has been at room temperature
for some days. That is part of what makes communication by email so
difficult. Those differences are usually quickly surfaced and
understood in a face-to-face conversation.
Regards,
John
Elizabeth Priddy on mon 11 sep 06
Thixotropy
Thixotropy is the property of some non-newtonian
pseudoplastic fluids to show a time-dependent change
in viscosity; the longer the fluid undergoes shear,
the lower its viscosity. However, this is not a
universal definition; the term is sometimes applied to
pseudoplastic fluids without a viscosity/time
component.
Many gels and colloids are thixotropic materials,
exhibiting a stable form at rest but becoming fluid
when agitated. Modern alkyd and latex paint varieties
are often thixotropic, and will not run off the
painter's brush, but will still spread easily and
evenly, since the gel-like paint "liquefies" when
brushed out. Some clays are also thixotropic, with
their behavior of great importance to structural
engineering, especially in earthquake zones. Clay-like
ground can practically liquefy under the shaking of a
tremor, greatly increasing the effect on buildings.
Landslips, such as those common in the cliffs around
Lyme Regis, Dorset and in the Aberfan, Wales slag heap
disaster are evidence of this phenomenon. Ketchup is
frequently thixotropic. Many clutch-type automatic
transmissions use fluids with thixotropic properties,
to engage the different clutch plates inside the
transmission housing at specific pressures, which then
changes the gearset.
Fluids which exhibit the opposite property, in which
shaking for a time causes solidification, are called
rheopectic and are much less common.
Etymology: Greek thixis, touch (from thinganein, to
touch) + -tropy, -tropous, from Greek -tropos, of
turning, from tropos, changeable, from trepein, to
turn.
--------------------------------------
I would say that the broader definition is the more
practical one to use rather than the jargonistic use
of thixopropic. It clearly describes the feature of
clay in the broader sense of how the world works and
so it will make things more clear rather than less
with regard to being able to talk to anyone about it
if you use the word the way every body does, not just
potters, and only some of them, it seems.
E
Elizabeth Priddy
Beaufort, NC - USA
http://www.elizabethpriddy.com
__________________________________________________
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Vince Pitelka on mon 11 sep 06
Ron Roy wrote -
> Yes - when you drop a hard lump of wet clay and it goes soft - then the
> clay is deflocculated to some extent. It must mean that some materials in
> the body are releasing something that is deflocking the body.
Ron -
Over the years I have had plenty of experience with stoneware bodies that
had been sitting for a long period of time and seemed very stiff, but when
dropped on the floor a few times or otherwise mobilized, the clay softened
to a good plastic consistency, and these bodies had no source for soluble
sodium. This just happened at Michael McDowells this summer when I did my
Ancient Clay workshop. The clay had been sitting in storage since the last
Ancient Clay workshop I did there three years ago. It's a recipe of mine
that Tacoma Clay Art Center mixes for us - equal parts fire clay, goldart,
ball clay, and extra fine grog - intended to approximate the bonfiring
claybodies made from local materials by tribal peoples. So there are no
sources of soluble sodium in that recipe, and once the clay is remobilized
it is beautifully plastic and workable, and thus obviously not
deflocculated. I have experienced the same thing with many stoneware bodies
that had only potash feldspar in them, and thus no source for sufficient
sodium to deflocculate the clay.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Ron Roy on tue 12 sep 06
Hi Ivor,
I'm saying that bentonite helps if clay is not plastic enough - or glazes
don't suspend well - thats all.
As I understand it - bacteria produce acid during their life cycles - which
then improves flocculation - which improves workability. If you add vinegar
to a clay slip you will see the thickening for instance.
RR
>Yes, I was aware that many minerals in clay will release metallic ions
>that have the ability to destroy or negate hydrogen bonding. Are you
>saying that Bentonite is of no consequence.
>
>I continue to wonder about the nature of Bacterial Action. What is about
>this process that causes the clay to improve. Carbonic acid seems a
>natural candidate in ensuring good plasticity with a high yield point
>since this is one of the two end products of bacterial decay or organic
>detritus.
>
>Best regards,
>
>Ivor
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Lee Love on tue 12 sep 06
On 9/11/06, Vince Pitelka wrote:
>
>
> Over the years I have had plenty of experience with stoneware bodies that
> had been sitting for a long period of time and seemed very stiff, but when
> dropped on the floor a few times or otherwise mobilized, the clay softened
> to a good plastic consistency, and these bodies had no source for soluble
> sodium.
>
Several of my non-industral clay bodies behave this way. I figured it
was because of soluables in the clay.
--
Lee in Mashiko, Japan
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
Vince Pitelka on tue 12 sep 06
Steve Slatin wrote:
> And now, having settled on the formulation "dramatic thixotropy" how
> about some suggestions regarding mixing up clay bodies that
> demonstrate "dramatic thixotropy?"
> I've got some sodium silicate, also some soda ash around somewhere,
> so roughly what's a good point to start at for experimenting? I don't
> want to turn the body all the way into casting sludge, I want to be able
> to pull it like taffy. Whack it like a pocupine. Pound it like a veal
> medallion.
Steve -
Normally, 1/4 of 1% of the dry weight of the clay is enough to deflocculate
a slip, but in another post there was some mention of over-deflocculation to
achieve extreme thixotropic behavior in clay. In deflocculating terra sig,
it seems generally agreed that a combination of sodium silicate and soda ash
works very well - I add 1/4 of 1% of each. So if you have access to some
soda ash you might want to try that. There is bound to be a point of
diminishing returns in the deflocculant addition, so I would try a range of
additions from 1/2% to 3% or 4% deflocculant of the dry weight of the clay,
which you can estimate by subtracting 25% of the wet weight. As you
probably know, once you achieve truly thixotropic clay, there's a pretty
limited range of things you can do with it. Mostly, you get clay shapes
that look like pulled taffy. As you can imagine, that gets old pretty
quick, and that's what happened when thixotropic clay was briefly popular
back in the 60s or 70s. A visual technique based on such a limited gimmick
doesn't really go very far. Then again, it might be in your destiny to
produce the great thixotropic clay masterpiece of all time.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Lee Love on tue 12 sep 06
On 9/12/06, Steve Slatin wrote:
>
>
>
> With apologies for asking an on-topic question, I remain,
> informationless --
"Interesting" is far more important than an authoritarian focus. ;^)
Nevertheless, Maybe Neph Sye can give you a clue:
Posted earlier from Nelson:
Also listed is a glaze for thixotropic clay body:
(Cone 5, crazes at Cone 9)
16 Kaolin (EPK)
24 Nepheline Syenite
60 Fetto Frit #3124
--
Lee in Mashiko, Japan
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
Ivor and Olive Lewis on tue 12 sep 06
Dear Ron Roy,
Yes, I was aware that many minerals in clay will release metallic ions =
that have the ability to destroy or negate hydrogen bonding. Are you =
saying that Bentonite is of no consequence.
I continue to wonder about the nature of Bacterial Action. What is about =
this process that causes the clay to improve. Carbonic acid seems a =
natural candidate in ensuring good plasticity with a high yield point =
since this is one of the two end products of bacterial decay or organic =
detritus.
Best regards,
Ivor
Ivor and Olive Lewis on tue 12 sep 06
Dear Elizabeth Priddy,=20
Please enlighten me. What is a "Pseudoplastic Fluid" ?=20
You can make an excellent Rheopectic (wonderful jargon) substance by =
mixing maize cornflour into soy sauce. If, as you are pouring this =
mixture from one utensil to another, you shake your pouring hand the =
stream of fluid will solidify and shatter into fragments. Attempt to =
stir it and again, it solidifies.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on tue 12 sep 06
Dear Vince Pitelka,=20
I appreciate your comments CA Digest (#2006 244)
I feel confused by the whole discussion. It seems as though there is a =
lot of imagination at work but very little science in what has been put =
forward so far.
The quality of Thixotropy must be incompatible with the quality of =
Plasticity. In the first case the material is classed as a "Non =
Newtonian fluid" so that it does not conform to the laws of a simple =
fluid such as free water, which the pottery world insists exists in a =
clay water mixture that appears to be solid. In the second we are =
speaking of a substance that behaves materially as though it were a =
uniform solid that has been heated to its forging temperature so that it =
can be freely shaped by the application of directed force.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Bruce Girrell on tue 12 sep 06
earlk wrote:
> Typically hydrogen
> bonds develop between two molecules when
> there is a slight charge separation such that
> the two molecules attract each other due to
> opposite electrical charge forces.
Earl,
Perhaps it was not clear from my description, but that is exactly what I was
trying to describe.
Vince Pitelka wrote:
>Freshly-mixed clay does not behave in a thixotropic
>fashion in any way.
But Vince, that's the same as saying that you see no thixotropic behavior if
you stir up a batch of thixotropic gel and look at it in the liquefied
state. The gel simply is observed in its low viscosity form. When you soften
a log of clay it takes time to re-establish its original stiffened state.
The liquefied gel or your special mix of clay may take less time to return
to its stiffened state, but time is not part of the definition of
thixotropy.
OK, when the original poster asked the question, she was looking for a
special recipe to create a clay to demonstrate thixotropy. I first asked she
was trying to demonstrate, as I was not clear exactly what she was looking
for. I wanted to let her know that thixotropy could be demonstrated without
the need for any special recipes and provided an example. Normal,
non-deflocculated clay demonstrates increased fluidity when mechanically
disturbed and, therefore, demonstrates thixotropy. If she wants to go to the
trouble of mixing a special recipe to demonstrate dramatic thixotropy, fine.
I was trying to save her some work.
Bruce Girrell
in cool, rainy northern Michigan
hopefully making his last post to this thread
Ron Roy on tue 12 sep 06
Hi Vince,
My experience is different - sometime there are raw materials we use that
carry enough sodium to have an effect - sometimes it's the water used to
mix the clay.
Perhaps we need to do some experiments - some clays with Epsom salts added
- to see if it is possible to make some clay that will not show the effect?
RR
>Ron Roy wrote -
>> Yes - when you drop a hard lump of wet clay and it goes soft - then the
>> clay is deflocculated to some extent. It must mean that some materials in
>> the body are releasing something that is deflocking the body.
>
>Ron -
>Over the years I have had plenty of experience with stoneware bodies that
>had been sitting for a long period of time and seemed very stiff, but when
>dropped on the floor a few times or otherwise mobilized, the clay softened
>to a good plastic consistency, and these bodies had no source for soluble
>sodium. This just happened at Michael McDowells this summer when I did my
>Ancient Clay workshop. The clay had been sitting in storage since the last
>Ancient Clay workshop I did there three years ago. It's a recipe of mine
>that Tacoma Clay Art Center mixes for us - equal parts fire clay, goldart,
>ball clay, and extra fine grog - intended to approximate the bonfiring
>claybodies made from local materials by tribal peoples. So there are no
>sources of soluble sodium in that recipe, and once the clay is remobilized
>it is beautifully plastic and workable, and thus obviously not
>deflocculated. I have experienced the same thing with many stoneware bodies
>that had only potash feldspar in them, and thus no source for sufficient
>sodium to deflocculate the clay.
>- Vince
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Vince Pitelka on tue 12 sep 06
Ivor Lewis wrote:
"The quality of Thixotropy must be incompatible with the quality of
Plasticity. In the first case the material is classed as a "Non Newtonian
fluid" so that it does not conform to the laws of a simple fluid such as
free water, which the pottery world insists exists in a clay water mixture
that appears to be solid. In the second we are speaking of a substance that
behaves materially as though it were a uniform solid that has been heated to
its forging temperature so that it can be freely shaped by the application
of directed force."
Ivor -
I suppose a sedimentologist who thoroughly understands the chemical states
of clay could explain this better. But as I see it, thixotropy in clay
depends on the electrical charge of the particles. Your statement above
seems to imply disbelief of the existence of "free water" in plast ic clay,
but of course it's a matter of scientific fact. Plastic clay behaves the
way it does because the platelets or kaolinite crystals have a natural
affinity for water, and thus tend to hold a water layer between the
particles. It seems in any system where particles are separated by water,
even a semi-solid like clay, a slight content of alkaline material causes
same charges in the particles, and thus they repel each other - that's
deflocculation, which destroys plasticity. In normal clay, even with the
water layers, there is still some friction, and thus the clay holds the form
we give it. Deflocculation reduces the friction, and what was a plastic
claybody becomes an uncontrollable jelly-like mass. A slight content of
acidic material causes opposite electrical charges in the particles, and
thus they attract one another - that's flocculation (the particles "floc"
together), and it makes the claybody more plastic.
It is important to recognize that both deflocculation and flocculation can
occur as clay ages. Some midrange and highfire claybodies contain soda
feldspars or neph sy, and sodium from these materials can disolve into the
water of plasticity, deflocculating the clay and rendering it unworkable
until the clay is re-flocculated. And of course flocculation is a natural
consequence of aging - the byproducts of naturally-occuring organic activity
are acidic and will flocculate the clay, increasing plasticity.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Vince Pitelka on tue 12 sep 06
Ron Roy wrote:
> Perhaps we need to do some experiments - some clays with Epsom salts added
> - to see if it is possible to make some clay that will not show the
> effect?
Ron -
My contention is that clays will still exhibit this behavior even if they
have not become deflocculated, and the experiment you propose would show
that. I think I'll give it a try.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Steve Slatin on tue 12 sep 06
RRRRRIIIIGGGHHHTT --
And now, having settled on the formulation "dramatic thixotropy" how
about some suggestions regarding mixing up clay bodies that
demonstrate "dramatic thixotropy?"
I've got some sodium silicate, also some soda ash around somewhere,
so roughly what's a good point to start at for experimenting? I don't
want to turn the body all the way into casting sludge, I want to be able
to pull it like taffy. Whack it like a pocupine. Pound it like a veal medallion.
With apologies for asking an on-topic question, I remain, informationless --
Steve Slatin
Bruce Girrell wrote:
OK, when the original poster asked the question, she was looking for a
special recipe to create a clay to demonstrate thixotropy. I first asked she
was trying to demonstrate, as I was not clear exactly what she was looking
for. I wanted to let her know that thixotropy could be demonstrated without
the need for any special recipes and provided an example. Normal,
non-deflocculated clay demonstrates increased fluidity when mechanically
disturbed and, therefore, demonstrates thixotropy. If she wants to go to the
trouble of mixing a special recipe to demonstrate dramatic thixotropy, fine.
I was trying to save her some work.
Bruce Girrell
---------------------------------
Get your email and more, right on the new Yahoo.com
Ivor and Olive Lewis on wed 13 sep 06
Dear Steve Slatin,=20
AS I said earlier, read Ed 4 of Glen Nelson. Shows good illustrations =
of "pulled taffy"
Once you have your deflocculated your clay allow the water to evaporate =
until you get a stiff sludge.
Or use the recipe I gave to Vince for an experiment but mix your =
defloccing agents in your water and cut the mass of water down to about =
10%. Let stand for 24 hours then mix. If you need more water spray with =
an atomiser.
Best regards,.
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on wed 13 sep 06
Dear Earl,
Nothing new in your Hydrogen Bond Theory. It is well explained by W.E. =
Brownell, "Industrial Ceramics", Ch 4. ISBN 3-211-81382-9, 1976.
An illustration of the strength of the hydrogen bond is the way it =
allows skaters to enjoy their sport, which would be impossible if water =
had an unpolarised molecule.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
.=20
Ivy Glasgow on wed 13 sep 06
This brings two questions to mind. Can just any clay be made thixotropic by
this approach, or are there some which don't respond to treatment with a
deflocculant? And, could just any clay be made into a casting slip?
I'm tuning in to this subject kind of late, so I apologize if this ground
has already been covered.
Ivy G, biding time and resting wrists till my pugmill arrives (woohoo!).
>Steve Slatin wrote:
> And now, having settled on the formulation "dramatic thixotropy" how
> about some suggestions regarding mixing up clay bodies that
> demonstrate "dramatic thixotropy?"
> I've got some sodium silicate, also some soda ash around somewhere,
> so roughly what's a good point to start at for experimenting? I don't
> want to turn the body all the way into casting sludge, I want to be able
> to pull it like taffy. Whack it like a pocupine. Pound it like a veal
> medallion.
>Steve -
>Normally, 1/4 of 1% of the dry weight of the clay is enough to deflocculate
>a slip, but in another post there was some mention of over-deflocculation >to
>achieve extreme thixotropic behavior in clay. In deflocculating terra sig,
>it seems generally agreed that a combination of sodium silicate and soda >ash
>works very well - I add 1/4 of 1% of each. So if you have access to some
soda ash you might want to try that. There is bound to be a point of
diminishing returns in the deflocculant addition, so I would try a range of
additions from 1/2% to 3% or 4% deflocculant of the dry weight of the clay,
which you can estimate by subtracting 25% of the wet weight. As you
probably know, once you achieve truly thixotropic clay, there's a pretty
limited range of things you can do with it. Mostly, you get clay shapes
that look like pulled taffy. As you can imagine, that gets old pretty
quick, and that's what happened when thixotropic clay was briefly popular
back in the 60s or 70s. A visual technique based on such a limited gimmick
doesn't really go very far. Then again, it might be in your destiny to
produce the great thixotropic clay masterpiece of all time.
Good luck -
- Vince
Vince Pitelka
Steve Slatin on wed 13 sep 06
Ivor --
I have Nelson and did mix a VERY small batch (100 g) from his
recipe --
frit 3110 -- 20
flint -- 10
EPK -- 15
Spodumene -- 15
F-4 Feldspar -- 15
Ball Clay -- 25
It handles 'sticky' but so far no taffy-pulling. I wonder if Nelson
left out a step involving adding additional Na?
I'm going to try Vince P's scheme of adding sodium silicate and
soda ash to wet clay next. Maybe having it rest for a week or
two will make a difference. I was literally scraping the bottom
of my F-4, so if it doesn't work I need to get a new bag of the
stuff to try again. And I really need to gear up production for
the next show, and stop experimenting ...
Steve Slatin
Ivor and Olive Lewis wrote:
Dear Steve Slatin,
AS I said earlier, read Ed 4 of Glen Nelson. Shows good illustrations of "pulled taffy"
Once you have your deflocculated your clay allow the water to evaporate until you get a stiff sludge.
Or use the recipe I gave to Vince for an experiment but mix your defloccing agents in your water and cut the mass of water down to about 10%. Let stand for 24 hours then mix. If you need more water spray with an atomiser.
Best regards,.
Ivor Lewis.
Redhill,
South Australia.
---------------------------------
Get your own web address for just $1.99/1st yr. We'll help. Yahoo! Small Business.
Ivor and Olive Lewis on thu 14 sep 06
Dear Steve Slatin,=20
I think the purpose of allowing the clay mixture, as Glen Nelson says, =
stand for long period is to get rid of a lot of the water.
Though I have no interest in thixotropic clay as a creative medium I do =
use a dewatered deflocculated slip as an adhesive. Works as well as =
Super Glue. But after I have deflocculated I do allow the fluid to loose =
water by evaporation ( not hard in my studio in summer) until it is like =
thick cream. I feel sure that with between 5% and 10% of water by weight =
is sufficient to give a very thick but mobile slurry that can be worked =
like "Taffy"
Many very fluid casting slips have as little a 15% by mass of water in =
the mixture and have the same flow characteristics as water
Fournier reports that excess deflocculant results in the clay taking on =
a jelly like consistency.
Hope your experiments are a success.
Best regards,
Ivor
Steve Slatin on fri 29 sep 06
Vince -- Thanks for the ideas. I decided to start with just one sodium source,
then try the other, then try them both together, using about half the range you
suggested -- first low, then trying high.
My thinking was that sodium silicate is stable (except in acids) and soda ash is acidic, so things get too complex right off if I start with both.
I made up sealed containers with 250 g each of clay (Vashon Buff), or an
estimated 200 g of dry clay each, with .5 to 4 grams of sodium silicate liquid
in .5 g steps.
The first day I checked at the 5 hour point; there was no visible effect -- the
SS was sitting on top of the clay. The next day (about 17 hours) I checked
again, still no visible change. Likewise at 22 hours.
The following day I was out of town, and the subsequent day there was visible
condensation on the inside of the containers. I checked, and the SS was no longer puddled up on top of the clay. When I opened the containers and checked the clay, the bottom of the clay in each of my sample containers was moist and workable, but the clay on the top of each sample was dry and 'crunchy.' I tried mixing the crunchy parts back in to see what that would do on some of the samples, and just for giggles worked the 3 g SS sample separately -- crunchy bits on one side, wet on another.
It was unusually workable, but no taffy effect.
I'll post again as I learn more.
-- Steve Slatin
Vince Pitelka wrote:
Steve -
Normally, 1/4 of 1% of the dry weight of the clay is enough to deflocculate
a slip, but in another post there was some mention of over-deflocculation to
achieve extreme thixotropic behavior in clay. In deflocculating terra sig,
it seems generally agreed that a combination of sodium silicate and soda ash
works very well - I add 1/4 of 1% of each. So if you have access to some
soda ash you might want to try that. There is bound to be a point of
diminishing returns in the deflocculant addition, so I would try a range of
additions from 1/2% to 3% or 4% deflocculant of the dry weight of the clay,
which you can estimate by subtracting 25% of the wet weight. As you
probably know, once you achieve truly thixotropic clay, there's a pretty
limited range of things you can do with it.
Steve Slatin --
The angel lay in a little thicket. It had no need of love; there was nothing anywhere in the world could startle it ...
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Vince Pitelka on sat 30 sep 06
> My thinking was that sodium silicate is stable (except in acids) and soda
> ash is acidic, so things get too complex right off if I start with both.
Steve -
I am curous as to where you got the idea that soda ash is acidic. On the
contrary, it is highly alkaline when disolved in water. Soda ash and sodium
silicate are completely compatible when used together as deflocculants. If
soda ash was acidic, the two would neutralize each other when used in
combination, and that certainly is not the case.
Good luck with your experiments.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Steve Slatin on mon 2 oct 06
Vince, Ivor --
(Vince) You're right! I was wrong. I'm going to continue with the tests, though, as
I've already pretty much completed the first round (no further changes as
of yesterday).
(Ivor) Your comments were also interesting, though I don't know
anything about the material you were using. I'm hoping with higher
concentrations of SS I'll start to get more interesting results. (Then
I'll switch to soda ash and run the same tests, then to a combination.)
It's been long enough since thixotropic clays were found interesting that
there's relatively little information about their preparation and so on; I'd
like to get enough info together so (whether I can find anything interesting
to do with it or not) there can be a base line of information for the next
interested person.
Thanks, guys. -- Steve Slatin
Vince Pitelka wrote:
Steve -
I am curous as to where you got the idea that soda ash is acidic. On the
contrary, it is highly alkaline when disolved in water. Soda ash and sodium
silicate are completely compatible when used together as deflocculants.
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Ivor and Olive Lewis on tue 3 oct 06
Dear Steve Slatin,=20
I have no objections to Sodium Silicate (SS) being used as a =
deflocculant. But there are good reasons to be cautious when using it.=20
I think it is recognised that if an excess is included in the clay/water =
paste it drives the pH well into the alkaline and has the effect of =
reflocculating the mixture. I think this could destroy the thixotropic =
property you are seeking.
The second point is that Sodium Silicate has exceptional fluxing =
properties encouraging melting at fairly low temperatures giving a =
strong solvent action as exemplified in some of the recipes for Zinc =
crystalline glazes. So you will have to take care when firing just in =
case the maturity point.of your clay changes.
The clay I used in my little test is Walkers PB 101, a white porcelain.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
=20
=20
Ivor and Olive Lewis on tue 3 oct 06
Lee Love,=20
That is an interesting observation.
How do you explain the occurrence of this property in a natural =
unprocessed substance. Surely this will be inconvenient when you are =
using such a material since physical force will cause it to change state =
from a plastic solid to a viscous fluid, lacking the strength to sustain =
its formal integrity.
Perhaps earth or soils with this property are responsible for mudslides, =
especially in localities where there is high rainfall and earthy =
termors.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Michael Wendt on tue 3 oct 06
Ivor,
The term I saw applied to such an event
in soils was "liquefaction".
During earthquakes, water saturated
sandy soils are no longer solid and as
happened in the giant earthquake in
the St. Louis, Missouri area in the mid
1800s, actually formed sand-water
geysers that buried adjacent structures.
I think that water is again the culprit.
It sticks things together and makes them
appear to be solid if left alone.
Once you reach the correct shear value,
the water behaves as a lubricant rather
than a bonding agent and the system
becomes fluid until hear values drop
below the critical threshold and the
near solid state again ensues.
Ivor wrote:
Lee Love,
That is an interesting observation.
How do you explain the occurrence of this property in a
natural unprocessed substance. Surely this will be
inconvenient when you are using such a material since
physical force will cause it to change state from a
plastic solid to a viscous fluid, lacking the strength
to sustain its formal integrity.
Perhaps earth or soils with this property are
responsible for mudslides, especially in localities
where there is high rainfall and earthy tremors.
Best regards,
Ivor Lewis.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Lee Love on tue 3 oct 06
I have mentioned that several of my non-industrial clays are
thixotropic. I think one advantage is that they seem to keep
workably soft longer because it is more difficult for the water to
evaporate in their harden state.
--
Lee in Mashiko, Japan
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
"When we all do better. We ALL do better." -Paul Wellstone
Ivor and Olive Lewis on wed 4 oct 06
Dear Michael Wendt,=20
Interesting historic information. But how does this relate to Lee Love's =
statement that one of the native clay bodies he uses is naturally =
thixotropic. Are you telling me that clay sediments have the same =
properties as grains of sand?
What I wish to know is the mineral content of that natural clay. Your =
information infers that it will contain a high proportion of Sand. Was =
this your intention ?
Thanks for your response.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Michael Wendt on thu 5 oct 06
Ivor wrote:
"Interesting historic information. But how does this
relate to Lee Love's statement that one of the native
clay bodies he uses is naturally thixotropic. Are you
telling me that clay sediments have the same properties
as grains of sand?
Ivor,
Exactly.
When we first got the samples of the
Moose Greek Feldspar, the lab had
wet ball milled the material for 24 hours.
It was amazing. In the bottom of the bucket,
it sat solid as rock.
We inverted the bucket on the table and
in a little while we heard what sounded
like breaking bisque hitting the table.
When we looked we saw stalactites
in flow off the bottom of the bucket
falling part way to the table before they
broke off and hit. They were solid
in appearance but gradually pooled and
settled flat on the table.
Examination of thixotropic clays at the
microscopic level might prove helpful
in determining why they behave as they
do?
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
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