Lee Love on sun 20 sep 09
On Sun, Sep 20, 2009 at 7:41 PM, Felicity Rich wrote:
> =3DA0 =3DA0 =3DA0 =3DA0Why does wedging clay increase plasticity?
>
Uniformity really helps in the workability of clay. Any clay
staying in a plastic bag for any amount of time, will end up with the
outer parts being wetter than the inner. And if it sits for a very
long time, then the outed gets harder than the inner clay..
If you deair pug, you don't really need to wedge, except to form the
hump you are going to throw.
--=3D20
--
Lee Love, Minneapolis
"The tea ceremony bowl is the ceramic equivalent of a sonnet: a
small-scale, seemingly constricted form that challenges the artist to
go beyond mere technical virtuosity and find an approach that both
satisfies and transcends the conventions." -- Rob Sliberman
full essay: http://togeika.multiply.com/journal/item/273/
Lee Love on sun 20 sep 09
One of the important aspects of wedging, is that it allows you to get
the feel of the clay, to know if it is softer or harder.
--
Lee Love, Minneapolis
"The tea ceremony bowl is the ceramic equivalent of a sonnet: a
small-scale, seemingly constricted form that challenges the artist to
go beyond mere technical virtuosity and find an approach that both
satisfies and transcends the conventions." -- Rob Sliberman
full essay: http://togeika.multiply.com/journal/item/273/
Felicity Rich on sun 20 sep 09
Why does wedging clay increase plasticity?
Bruce Girrell on sun 20 sep 09
Felicity Rich wrote:
Why does wedging clay increase plasticity?
If I understand what you are asking...
Here's the way that I understand things:
As clay sits around, the clay particles and water molecules rearrange at a =
=3D
microscopic scale, allowing the negative and positive bits to move toward a=
=3D
more stable state. That is, things wiggle around a bit until the electrica=
=3D
l forces become more balanced. That means that the negatives and positives =
=3D
will tend to cling together a bit more than just after the clay was initial=
=3D
ly put in place.* The clay will feel stiffer, though its inherent propertie=
=3D
s have not changed.
Moving the clay/water mass around disrupts this more tidy arrangement and t=
=3D
he clay feels more workable. Again, the inherent properties of the clay hav=
=3D
e not changed. But the more tidy electrical arrangement will be disrupted b=
=3D
y mechanical motion, so that the negatives and positives are less strongly =
=3D
bound to one another, allowing more ease of movement of the mass.
Even without wedging, this effect can be observed. Take a bag of clay that =
=3D
has been sitting around for a while and feels stiff. Drop it on the floor a=
=3D
couple of times. When you feel it again, you will notice that it feels sig=
=3D
nificantly less stiff. Wedging, of course, is much more effective than simp=
=3D
ly dropping the bag, providing homogenization of the mixture and a uniformi=
=3D
ty of properties.
Ivor may have something to say about this
Bruce Girrell
* One theory suggests that the water shell around the clay particles takes =
=3D
on a structured form, akin to that of ice=3D
Snail Scott on sun 20 sep 09
On Sep 20, 2009, at 7:41 PM, Felicity Rich wrote:
> Why does wedging clay increase plasticity?
Because it gets all the little platelets lined up in
the same orientation, making the surface tension
between the particles work more effectively.
Making a coil or rolling a slab has a similar effect,
but not so thoroughly.
-Snail
ivor & olive lewis on mon 21 sep 09
Dear Bruce and Dear Felicity,
I really have nothing to say. Spend hours leafing through those wonderful
text books that are written for potters and get no reliable, readily
testable answers.
As a simplistic model I have to agree with Bruce's summary. Except that, if
all the negative charges marry all of the positive charges on a one to one
basis so that the mass is electrostatically neutral then the degree of forc=
e
needed to cause one part to move against another would make the substance
unworkable. When the yield point was reached the mass would shatter ! ! !
But things are happening to ageing clay at Redhill that are difficult to
explain without invoking the fact that I live near an active fault that
occasionally slips releasing an Earth tremor. Then I find aged pugs of clay
that are fractured across and have broken surfaces that have the appearance
of cast iron that has been fractured with a sledge hammer. Yes, all the
visual qualities of a brittle fracture in a material that is supposed to be
"Plastic".
What I regard as a rational explanation for the occurrence of workability i=
n
plastic clay is regarded as heresy when compared to popular public
information and "Common Sense".
Sincere regards to you both,
Ivor Lewis,
Redhill,
South Australia
Patty on mon 21 sep 09
A Proposal
Someone with access to a really powerful microscope maybe even an electron
microscope should get funding to examine the clay before and after wedging
to see if the platelets, or molecules or even the electrons change
orientation after wedging. Or the spaces between the particles, or
molecules. Or the sizes of the particles or spaces between them. They
could than compare clay from various pugmills, vacuumed or not, pugged vs
wedged. Ramshead vs spiral, on the wedging table or on the wheel, male
potter or female potter. Think of all the data that could be collected.
The claims suppliers could make for their products. What fun.
Patty Kaliher
steve graber on tue 22 sep 09
ok, i'm just guessing a little here from some observations but clay seems t=
=3D
o have a thixotropic property and can change from semi solid to semi liquid=
=3D
when distrubed.=3DA0 =3D0Ahttp://education.yahoo.com/reference/dictionary/=
entr=3D
y/thixotropy=3D0A=3D0Anote most raku glazes do the same thing.=3DA0 when th=
ey sit=3D
in their buckets, they become like a solid.=3DA0 shake a brush in it, and =
it=3D
loosens up into a glaze again.=3DA0 =3D0A=3D0A=3DA0Steve Graber, Graber's =
Pottery,=3D
Inc=3D0AClaremont, California USA=3D0AThe Steve Tool - for awesome texture=
on =3D
pots! =3D0Awww.graberspottery.com steve@graberspottery.com =3D0A=3D0A=3D0AO=
n Laguna=3D
Clay's website=3D0Ahttp://www.lagunaclay.com/blogs/ =3D0A=3D0A=3D0A=3D0A=
=3D0A_________=3D
_______________________=3D0AFrom: Patty =3D0ATo: Cl=
ayar=3D
t@LSV.CERAMICS.ORG=3D0ASent: Monday, September 21, 2009 1:15:17 PM=3D0ASubj=
ect:=3D
Re: Why does wedging clay increase plasticity?=3D0A=3D0AA Proposal=3D0A=3D=
0ASomeon=3D
e with access to a really powerful microscope maybe even an electron=3D0Ami=
cr=3D
oscope should get funding to examine the clay before and after wedging=3D0A=
to=3D
see if the platelets, or molecules or even the electrons change=3D0Aorient=
at=3D
ion after wedging.=3DA0 Or the spaces between the particles, or=3D0Amolecul=
es.=3D
=3DA0 Or the sizes of the particles or spaces between them.=3DA0 They=3D0Ac=
ould t=3D
han compare clay from various pugmills, vacuumed or not, pugged vs=3D0Awedg=
ed=3D
.=3DA0 Ramshead vs spiral, on the wedging table or on the wheel, male=3D0Ap=
otte=3D
r or female potter.=3DA0 Think of all the data that could be collected.=3D0=
AThe=3D
claims suppliers could make for their products.=3DA0 What fun.=3D0A=3D0APa=
tty Ka=3D
liher=3D0A=3D0A=3D0A=3D0A
Ron Roy on thu 24 sep 09
I agree - particle alignment, remixes, gets you in touch - good time to
adjust consistency - all that - and - refreshes oxygen so bacteria start
working again - also a good time to introduce some old clay -that has lots
of bacteria. Remember - bacteria produce acid which promotes plasticity - s=
o
wedging improves workability on many levels. Still - you can formulate cla=
y
that never needs aging which will work right out of the box or right out of
the pug mill - the best clay however is the aged stuff - especially when
pulling handles.
RR
On Sun, Sep 20, 2009 at 8:41 PM, Felicity Rich wrote:
> Why does wedging clay increase plasticity?
>
--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
Jess McKenzie on fri 25 sep 09
Ron, may we then conclude that it is better to buy the oldest
stuff (by date of pugging/packaging) then re-wedge it for
water homogeneity?
Another question: If dropping pH aids plasticity, how about
adding some organic acid, like citric acid? Or would amino
acids be more likely to do the trick? We'd always guessed
it's the bacterial protein that makes clay more plastic, but
adding acids might be do-able.
Just thoughts--thanks...~joan and jess in Sequim, WA
To: Clayart@LSV.CERAMICS.ORG
[ Double-click this line for list subscription options ]
I agree - particle alignment, remixes, gets you in touch -
good time to adjust consistency - all that - and - refreshes
oxygen so bacteria start working again - also a good time to
introduce some old clay -that has lots of bacteria. Remember -
bacteria produce acid which promotes plasticity - so wedging
improves workability on many levels. Still - you can
formulate clay that never needs aging which will work right
out of the box or right out of the pug mill - the best clay
however is the aged stuff - especially when pulling handles.
RR
On Sun, Sep 20, 2009 at 8:41 PM, Felicity Rich
wrote:
> Why does wedging clay increase plasticity?
>
--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
ivor & olive lewis on sat 26 sep 09
Ron Roy,
Good list Ron.
But you forgot the important idea the old timers incorporated. Wedging the
clay up and leaving it to age was not sufficient to get the best working
properties from any clay. It had to be aged for a long period but also
wedged and kneaded repeatedly and frequently, daily or even several times a
day.
In more recent times that instruction was also applied to clay that was
being processed via the mechanical auger pug mill, with or without suction.
A batch has to be passed through the mill several times for optimal results=
.
Perhaps this is the cause of the increased resistance to deformation toward=
s
the end of a kneading cycle, a fact which has been commented on before
The greatest cause of benefit would have to be the diminution of particle
size, splitting the crystals parallel to their faces. Each time individual
crystals are split the area exposed to water doubles. If no more water is
added to the paste then the thickness of the water layer is halved, binding
forces act over a shorter distance and the result is greater mechanical
strength.
Best regards
Ivor Lewis,
Redhill,
South Australia
Steve Mills on sat 26 sep 09
I'm going to stick my nose in here:
All my recycled Clay has half a cup-full of home made Cider Vinegar added t=
o it, and after less than a month has improved plasticity beyond belief (wh=
en you cut it the middle is noticeably darker).
The old time Potters used to pee on their stored clay to get the same resul=
t, but cider vinegar smells nicer!
Steve Mills
Bath
UK
________________________________
From: Jess McKenzie
To: Clayart@LSV.CERAMICS.ORG
Sent: Friday, September 25, 2009 5:06:34 PM
Subject: Re: Why does wedging clay increase plasticity?
Ron, may we then conclude that it is better to buy the oldest
stuff (by date of pugging/packaging) then re-wedge it for
water homogeneity?
Another question: If dropping pH aids plasticity, how about
adding some organic acid, like citric acid? Or would amino
acids be more likely to do the trick? We'd always guessed
it's the bacterial protein that makes clay more plastic, but
adding acids might be do-able.
Just thoughts--thanks...~joan and jess in Sequim, WA
To: Clayart@LSV.CERAMICS.ORG
[ Double-click this line for list subscription options ]
I agree - particle alignment, remixes, gets you in touch -
good time to adjust consistency - all that - and - refreshes
oxygen so bacteria start working again - also a good time to
introduce some old clay -that has lots of bacteria. Remember -
bacteria produce acid which promotes plasticity - so wedging
improves workability on many levels. Still - you can
formulate clay that never needs aging which will work right
out of the box or right out of the pug mill - the best clay
however is the aged stuff - especially when pulling handles.
RR
On Sun, Sep 20, 2009 at 8:41 PM, Felicity Rich
wrote:
> Why does wedging clay increase plasticity?
>
--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
Jess McKenzie on sat 26 sep 09
Thanks, Steve. Both are weakly acidic, of course. Vinegar
has a nominal pH of about 2.5; urine about 6. How much clay
receives the half-cup of vinegar, approximately?
~joan and jess
Steve Mills wrote:
I'm going to stick my nose in here: All my recycled Clay has
half a cup-full of home made Cider Vinegar added to it, and
after less than a month has improved plasticity beyond belief
(when you cut it the middle is noticeably darker). The old
time Potters used to pee on their stored clay to get the same
result, but cider vinegar smells nicer!
marci and rex on sat 10 oct 09
At 09:26 PM 10/10/2009, Neon-Cat wrote:
> Each time the subject has come up over the=3D20
> last two years I=3DE2=3D80=3D99ve been on clayart I=3DE2=3D80=3D99ve=3D20
> made a point to deepen my knowledge in this=3D20
> fascinating subject area but just can=3DE2=3D80=3D99t=3D20
> reconcile vinegar in the clayart-way as a=3D20
> beneficial substance that =3DE2=3D80=3D9Ccertainly does=3D20
> flocculate clay=3DE2=3D80=3D9D. So show me. Prove it to me=3D20
> and other list members, 'cause right now it's=3D20
> like nails-on-a-chalkboard-irritating each time I encounter such=3D
statements.
I dont have the knowledge that Vince=3D20
and the others on this board do ... but all I=3D20
know is that I can take porcelain slurry and=3D20
add a little vinegar and it thickens right up=3D20
... ( too much and it thickens up like=3D20
melted chocolate seizing when=3D20
you get water in it ) As I understand=3D20
it, THAT's flocculation ... clay particles coming together...
Maybe Im missing something here .... ?
marci aka Captain Obvious
www.ppio.com
Vince Pitelka on sat 10 oct 09
Neon-Cat wrote:
"In all the world of science I=3DE2=3D80=3D99ve explored only you, Vince, a=
nd =3D
a few other clayarters have repeatedly stated that vinegar will =3D
flocculate clay. What do you guys know that scientists for well over =3D
fifty years have missed?"=3D20
Marian -=3D20
I know what I know from experience, but I don't know the science, =3D
really. I show my students how a flocculant can work in a slip mixture, =
=3D
and since the effect involves particles separated by water, and plastic =3D
clay involves particles (partially) separated by water, the same =3D
principles seem to apply. I don't need to test it, because I know it =3D
works. Claybodies containing soda feldspars will deflocculate =3D
themselves over time, and vinegar or Epsom salts will counteract this =3D
and re-flocculate the claybody. This is well-known information, and =3D
there doesn't seem to be any mystery there, so I am not sure what you =3D
are asking. =3D20
You say: "I've always hated the idea of using vinegar in claywork." =3D20
Why? Have you physically witnessed how an addition of vinegar can =3D
"cure" a thixotropic claybody? Have you ever done repairs to bone-dry =3D
clay with a paper-clay slip made from powdered claybody, paper pulp, and =
=3D
vinegar? It's an amazing experience.
You ask: "What do you guys know that scientists for well over fifty =3D
years have missed?"
Plenty, apparently. I was raised by scientists, and I certainly support =
=3D
scientific inquiry, but the scientists are not working hands-on with =3D
clay on a daily basis in the studio and do not have the experience with =3D
the material that a life-long professional studio artist has. Ron might =3D
be able to explain it scientifically, but it's much more important that =3D
it just works. I understand your scientific curiosity, but it shouldn't =
=3D
bother you that we use these terms and that flocculation is a real issue =
=3D
in claybodies, even if the scientists have not researched this. =3D
Craftspeople and tradespeople who work with a material full-time through =
=3D
their lives find out all sorts of things that the scientists have never =3D
researched or discovered. The sophisticate scientific inquiry into clay =3D
properties and behavior has gone on for only a very small fraction of =3D
the time that potters have been accumulating practical information about =
=3D
its properties and behavior.=3D20
It sounds like this is a line of scientific inquiry that you are primed =3D
to delve into. We will be most interested in your findings.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
=3D20
Neon-Cat on sat 10 oct 09
On Thu Oct 8, 2009 9:30 pm Ron wrote: =3DE2=3D80=3D9CJust a warning - if us=
ing vi=3D
negar - and it certainly does flocculate clay - however - if you plan to st=
=3D
ore your clay for more than a few weeks it can get pretty foul - some have =
=3D
complained they could not use it for the smell.
Epsom Salts does the same thing without the stink.=3DE2=3D80=3D9D
Ron,=3D20
Just so we=3DE2=3D80=3D99re on the same page, please tell me=3D20
1. What you mean by flocculation.=3D20
In clay science flocculation typically refers to processes of clay particle=
=3D
agglomeration in aqueous solutions (water-clay systems). Potters are most =
=3D
familiar with the term as it is applied to processes affecting slips, slurr=
=3D
ies, and glazes.=3D20
A clay body is a solid (solution) with water and gas phases.=3D20
In soil science flocculation refers to the aggregation of soil particles so=
=3D
me of which may be clay particles.=3D20
When you write =3DE2=3D80=3D9Cflocculate=3DE2=3D80=3D9D in reference to cla=
y bodies do =3D
you have in mind a definition from one of these two disciplines or somethin=
=3D
g else entirely?
2. Please explain the mechanism for clay flocculation by vinegar (dilute ac=
=3D
etic acid).=3D20
Your use of the term flocculate implies that a mechanism is known.=3D20
In all the world of science I=3DE2=3D80=3D99ve explored only you, Vince, an=
d a fe=3D
w other clayarters have repeatedly stated that vinegar will flocculate clay=
=3D
. What do you guys know that scientists for well over fifty years have miss=
=3D
ed?=3D20
For simplicity=3DE2=3D80=3D99s sake you may confine your answer to clay bod=
ies co=3D
ntaining only kaolinite.
I am very sincerely serious with these two questions as the subject often a=
=3D
ppears and bold statements without explanation are made that contradict the=
=3D
findings of others and my own understanding. I=3DE2=3D80=3D99ve always hat=
ed the=3D
thought of using vinegar in clay work. Each time the subject has come up o=
=3D
ver the last two years I=3DE2=3D80=3D99ve been on clayart I=3DE2=3D80=3D99v=
e made a poi=3D
nt to deepen my knowledge in this fascinating subject area but just can=3DE=
2=3D
=3D80=3D99t reconcile vinegar in the clayart-way as a beneficial substance =
that=3D
=3DE2=3D80=3D9Ccertainly does flocculate clay=3DE2=3D80=3D9D. So show me. =
Prove it to =3D
me and other list members, 'cause right now it's like nails-on-a-chalkboard=
=3D
-irritating each time I encounter such statements. I also feel increasingly=
=3D
dismayed imagining folks needlessly junking-up their clay bodies until one=
=3D
of their precious resources becomes so down-right nasty they don't want to=
=3D
use it.=3D20
Marian
Neon-Cat
www.neon-cat.com
http://www.flickr.com/photos/neon-cat/
James Freeman on sun 11 oct 09
On Sat, Oct 10, 2009 at 10:26 PM, Neon-Cat wrote:
>
> Ron,
> Just so we=3D92re on the same page, please tell me
> 1. What you mean by flocculation.
>
> 2. Please explain the mechanism for clay flocculation by vinegar (dilute
> acetic acid).
>
> So show me. Prove it to me and other list members, 'cause right now it's
> like nails-on-a-chalkboard-irritating each time I encounter such statemen=
=3D
ts.
>
Hi, Marian...
It has been my understanding that the acids do not flocculate the clay per
se, but rather the acid's effect on pH (acidity/alkalinity) creates the
conditions which favor flocculation. In effect (and probably simplified),
clays flocculate more readily in acidic (low pH) conditions than they do in
higher pH conditions. The vinegar or other acid "primes the pump", creatin=
=3D
g
favorable conditions for whatever magic power causes flocculation. So for
Ron, Vince, Pinnell, and many others to say that vinegar flocculates clay i=
=3D
s
not materially inaccurate in our non-scientific arena. Saying that vinegar
"creates the conditions that allow and encourage flocculation" may be more
accurate, but the difference in our situation seems to be negligible. It
also seems unnecessary for us as potters to understand flocculation on an
electrochemical level so long as our practical understanding of what acids
do to clay does not run counter to the science, and in this case it seems
not to.
I wanted to double-check my understanding to make sure I was not totally of=
=3D
f
base (I am not a chemist), and quickly found the following scholarly
mish-mash which seems to support my understanding. It is from a paper
entitled EFFECT OF SATURATING CATION, pH, AND ALUMINUM AND IRON OXIDE ON TH=
=3D
E
FLOCCULATION OF KAOLINITE AND MONTMORILLONITE, from the journal, Clays and
Clay Minerals, Vol. 35, No. 3, 220-227, 1987. You ca find the entire papre
here: http://www.clays.org/journal/archive/volume%2035/35-3-220.pdf . I
have cut and pasted the citation, so I hope the formatting is not too
screwed up.
Effect of pH on flocculation-dispersion
behavior of clays
The flocculation-dispersion behavior of phyllosilicares
(Swartzen-Allen and Matijevic, 1976; Arora and
Coleman, 1979) and two arid-zone soils (Suarez et al.,
1984) has been found to depend on pH. Arora and
Coleman (1979) found that in electrolyte solutions of
NaC1 at pH 7.0, NaHCO3 at pH 8.3, and NaECO 3 at
pH 9.5 the CCC for most of the Na-clays studied was
highest in the NaHCO3 solution; however, interpretation
of these data is difficult because pH was not
measured in the presence of the clays. Swartzen-Allen
and Matijevic (1976) found that the CCCs for both Namontmorillonite
and Na-kaolinite in NaNO3 solution
increased with increasing pH from 1 meq/liter at pH
3.8 to l0 meq/liter at pH 10 and from 2 meq/liter at
pH 4.1 to 40 meq/liter at pH 10.1, respectively. Thus,
the pH effect was much greater for Na-kaolinite. Suarez
et aL (1984) found that hydraulic conductivity of two
arid-zone soils containing mixtures of clays decreased
from pH 6 to 9; dispersion increased with increasing
pH for both the predominantly kaolinitic and the
montmorillonitic soil. These authors suggested that the
pH effect in their soils was due to the presence of variable
charge minerals and organic matter. At low pHs
these materials were positively charged and bonded to
the negatively charged faces of the phyllosilicates. At
high pHs, however, they underwent charge reversal,
contributed negative charge to the system, and thereby
increased dispersion of the system.
Take care.
...James
James Freeman
"All I say is by way of discourse, and nothing by way of advice. I should
not speak so boldly if it were my due to be believed."
-Michel de Montaigne
http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/clayart/
Neon-Cat on mon 12 oct 09
Ivor wrote:=3D20
=3DE2=3D80=3D9DFrank Hamer in his Dictionary 1st Edition covers the second =
point =3D
under the heading of Flocculation and Flocculants giving equations for the =
=3D
effects of Hydrochloric acid (p129) and definitions and uses (page 127). Ha=
=3D
mer states that the effect of acetic acid is of short duration.=3DE2=3D80=
=3D9D (s=3D
nip)
=3DE2=3D80=3D9DIn my opinion these issues can only be addressed if we disre=
gard o=3D
ur previous learning and preconceptions.=3DE2=3D80=3D9D
OK, other than personal experiences I see where some of you are getting vin=
=3D
egar as a flocculant. The Potter's Dictionary of Materials and Techniques, =
=3D
Fifth Edition, under flocculants talks of treating suspensions and offers t=
=3D
his on page 147:
=3DE2=3D80=3D9CFlocculants are acids or salts which act as acids.=3DE2=3D80=
=3D9D Vinega=3D
r is listed as a flocculant with the caveat =3DE2=3D80=3D9Cbut its effect i=
s not =3D
permanent. The treated suspension will slowly return to its original fluidi=
=3D
ty over a couple of weeks.=3DE2=3D80=3D9D The Dictionary did offer some equ=
ations=3D
for the dissociation of hydrochloric acid but not for acetic acid (vinegar=
=3D
). Had they looked at the reactions for acetic acid they might have left vi=
=3D
negar off their list and out of other discussions involving flocculants. On=
=3D
page 209 the Hamer dictionary refers to vinegar (and fruit juices) as a st=
=3D
rong acids and this just isn=3DE2=3D80=3D99t so in the world of chemistry. =
Please=3D
be aware that acetic acid is a carboxylic acid, an organic acid, not a min=
=3D
eral or inorganic acid like HCl.=3D20
Here is the reaction for acetic acid in water:
CH3COOH (aq) <---> CH3COO- (aq) + H+ (aq)
(H+ is shorthand for the hydronium ion, H3O+)
Equilibrium favors the left side of the equation. The covalent acetic acid=
=3D
breaks up into hydrogen ions and acetate anions, but these ions recombine =
=3D
to form acetic acid as fast as it dissociates. Primarily we have acetic aci=
=3D
d molecules in solution =3DE2=3D80=3D93 not ions. At higher working pHs, mo=
re ace=3D
tic acid will dissociate. Because of its characteristics as a weak acid, ac=
=3D
etic acid is often used as a pH buffer and stabilizer for solutions -- to c=
=3D
hange the pH of a solution buffered by acetic acid takes quite a lot of exc=
=3D
ess acid or base.=3D20
James wrote: =3DE2=3D80=3D9CIt has been my understanding that the acids do =
not fl=3D
occulate the clay per se, but rather the acid's effect on pH (acidity/alkal=
=3D
inity) creates the conditions which favor flocculation. (snip) =3DE2=3D80=
=3D9DIt =3D
also seems unnecessary for us as potters to understand flocculation on an e=
=3D
lectrochemical level so long as our practical understanding of what acids d=
=3D
o to clay does not run counter to the science, and in this case it seems no=
=3D
t to.=3DE2=3D80=3D9D
Thanks for the note James. I do think it is important for us potters to be =
=3D
able to communicate with the rest of the world. And to use terms correctly =
=3D
and grasp basic concepts especially if we=3DE2=3D80=3D99re going to be talk=
ing ab=3D
out =3DE2=3D80=3D9Cwell flocculated clay bodies=3DE2=3D80=3D9D =3DE2=3D80=
=3D93 it seems to me=3D
that would require at least a basic knowledge of flocculation mechanisms o=
=3D
r the nature of the acid in use from those doing the talking. That others h=
=3D
ave researched and found acetic acid to be a deflocculant or soil dispersiv=
=3D
e makes me wonder. And like others I have to wonder how flocculated we want=
=3D
a clay body anyway =3DE2=3D80=3D93 the only thing we can flocculate except=
maybe=3D
a well ground feldspar or another non-plastic we=3DE2=3D80=3D99ve managed =
to mak=3D
e act as a colloid, are clay particles in normal studio pottery practice. I=
=3D
n a clay body we want good consistency which involves many physical propert=
=3D
ies, not just plasticity or clay particle aggregation. If all our clay part=
=3D
icles crowded into one area
of the dance floor, then what? Little silica particles and feldspars and w=
=3D
hat-have-you=3DE2=3D80=3D99s would be left out in the cold on their end of =
the fl=3D
oor. I jest, but you get the point.=3D20
In the article you site you will see that they were using Na-kaolin, not re=
=3D
gular old kaolin clay like we potters use and that is most often found in n=
=3D
ature. In the run-of-the-mill kaolin particle, its very small charge is not=
=3D
pH dependent since it results from structural defects =3DE2=3D80=3D93 isom=
orphic=3D
substitution which is usually neutralized by additional isomorphic substit=
=3D
ution elsewhere in the structure. Examples of isomorphic substitution are S=
=3D
i4+ by Al3+ in the tetrahedral layer or Al3+ by Mg2+ or vice versa in the o=
=3D
ctahedral layer. Besides layer charge, the other source of possible charge =
=3D
is at mineral edges through protonation and deprotonation reactions. These =
=3D
would be most noticeable when kaolin is mined and first processed or if a p=
=3D
otter goes to a lot of trouble to mill, delaminate, and separate his/her ka=
=3D
olin particles. By the time we get kaolin into a slip, glaze, or clay body =
=3D
it is usually no longer just a mix of single clay crystal particles but a
charge-satisfied mix of aggregated particles with a minimum size composed =
=3D
of 4-10 tactoids each composed of 4-9 individual particles. At any rate, th=
=3D
e kaolin displays low surface reactivity as measured by its cation exchange=
=3D
capacity (CEC) =3DE2=3D80=3D93 much lower than the illite or montmorilloni=
te (be=3D
ntonite) clays we might also be familiar with or the natural or synthetic N=
=3D
a-kaolins. In nature and in a clay body or a suspension like those we are w=
=3D
orking with, the small negative or positive charge has already be satisfied=
=3D
(balanced). The clay particle is hydrated and surrounded by a water layer =
=3D
and then a second layer of water containing additional ions. For adsorption=
=3D
onto an unsatisfied charged clay particle edge, an ion has to have somethi=
=3D
ng going for it that will make it competitive with what else is available i=
=3D
n the mix and it will have to be able to get to the edge itself and make a =
=3D
good fit, all while traveling exceedingly fast. =3D20
Using vinegar is a problem since it is dilute acetic acid. Acetic acid is a=
=3D
weak acid with a weak conjugate base. Its pKa is 4.75 at 25 degrees C. The=
=3D
zero charge for kaolinite is approximately pH 4.7. This is the point at wh=
=3D
ich the diffuse layer charge, if any, equals zero. See the problem? Kaolin =
=3D
and vinegar just won=3DE2=3D80=3D99t be very reactive. Couple this with the=
fact =3D
that we will only have a small number (0.4 - 1.0%) of acetate anions availa=
=3D
ble for adsorption, and only a small number of protons released from the vi=
=3D
negar and there is not much chance that vinegar could change the surface or=
=3D
edge charge of a clay particle. In water, acetic acid tends to cause water=
=3D
to want to give up a proton and thus become basic.=3D20
=3D20
Marian, page 1, see next post=3D20
Neon-Cat on mon 12 oct 09
page 2
We do have a slight viscosity change using vinegar in a clay body or slip. =
=3D
Where the viscosity of water at 20 degrees C is 1.0 cP, the viscosity of ac=
=3D
etic acid is 1.22 cP. This may lead to some slight increase in the =3DE2=3D=
80=3D
=3D98thickness=3DE2=3D80=3D99 of a clay body or slurry especially when the =
effects =3D
of vinegar are considered in the context of the other clay body or slip ing=
=3D
redients. Besides, if nothing else, we=3DE2=3D80=3D99ve added the acetic ac=
id mol=3D
ecules themselves. As un-dissociated molecules they=3DE2=3D80=3D99re just g=
oing t=3D
o be hanging out, adding to the carbon load. It should be pointed out that =
=3D
water salinity affects viscosity and diffusivity so the vinegar may very we=
=3D
ll be reacting with any salts or non-clay particles in our clay bodies and =
=3D
slips.=3D20
In a slip or slurry, Brownian motion and Debye-H=3DC3=3DBCckel interactions=
wil=3D
l always contribute positively to the viscosity. The structural tightening =
=3D
of hydrated ions or the loosening of unhydrated ions increasing or decreasi=
=3D
ng the strength of the bonds (called the structural temperature effect) wil=
=3D
l alter the viscosity of the clay-water solution either positively or negat=
=3D
ively depending on the type of salts we have in the mix and the temperature=
=3D
at which we are mixing or using our product. I should point out again that=
=3D
the acetic acid in vinegar is most often, for our purposes, mostly un-diss=
=3D
ociated molecules of acetic acid and the interesting thing is they usually =
=3D
come paired in a structure called a dimer. Dimers are held together by stro=
=3D
ng hydrogen bonds and associate with each other and water as water does wit=
=3D
h itself =3DE2=3D80=3D93 through strong hydrogen bonding. I could see our l=
ittle =3D
clay particles bound tighter to each other under the influence of a=3D20
water-vinegar bonding and buoyed in such a solution. These mechanisms (vis=
=3D
cosity changes and tighter hydrogen bonding) might account for a thickening=
=3D
of a clay-water solution and seeming flocculation effects.=3D20
As a reminder, the only place reactions can take place in a clay body is at=
=3D
the solid-water phase interface. In slips and glazes our plastic and non-p=
=3D
lastic particles are in a water-based solution where plenty of interaction =
=3D
is possible, and there=3DE2=3D80=3D99s plenty of room for everything to mov=
e abou=3D
t so comparing slip flocculation with clay body flocculation is not always =
=3D
the way to go. In a clay body the reaction arenas are narrow channels, pore=
=3D
s, and capillaries within a confining solid. Only the walls of these mini-t=
=3D
unnels react with the water or what=3DE2=3D80=3D99s in the water. I would, =
for ex=3D
ample, never propose to judge a clay body by what=3DE2=3D80=3D99s settled i=
n the =3D
throwing water used during the course of a day=3DE2=3D80=3D99s time. Ridicu=
lous! =3D
That would be like asking us to comment on the remnants of Vince after some=
=3D
one had axed him to bits and thrown him in the swimming pool behind the Cla=
=3D
yart Pub =3DE2=3D80=3D93 what correlation could we possibly make between th=
e piec=3D
es in the pool and the=3D20
once living Vince? (just kidding Vince =3DE2=3D80=3D93 I needed an example=
). See=3D
the problem with this type of approach?=3D20
Back to our clay body =3DE2=3D80=3D93 we=3DE2=3D80=3D99re dousing it with v=
inegar. Much=3D
acetic acid will remain as acetic acid molecules in dimers, some will be a=
=3D
ble to act as an anionic deflocculant with its acetate anion (CH3COO-) bond=
=3D
ing to kaolin particles positive edge surfaces. In industry acetic acid is =
=3D
not popular as a deflocculant because it is a weak acid with a small organi=
=3D
c chain and other compounds work much better and more reliably. It is used =
=3D
as a buffer in soil tests (soil almost always contains clay) and aqueous so=
=3D
lutions in many others fields, food science included. As an organic acid it=
=3D
does cause problems in nature (soil dispersion and erosion) and in clays u=
=3D
sed to line landfills or hazardous containment sites. Acetic acid biodegrad=
=3D
es in soil and water, readily leaches from soils, and shows a loss of about=
=3D
12.3% per hour in muddy water. It evaporates from dry surfaces at a rate o=
=3D
f 0.97 (n-Butyl acetate=3D3D1) but does not volatilize significantly from w=
at=3D
er.=3D20
So, we're managing to create some turbulence by dousing our clay body with =
=3D
vinegar. It would be like a herd of sheep running through our happy little =
=3D
Clayart Pub =3DE2=3D80=3D93 lots of confusion, things bouncing around, coll=
iding,=3D
getting destroyed, structure hammered with some ions (e.g. Al) shaken free=
=3D
, pH wavering back and forth, ions coupling and uncoupling, etc., etc. as v=
=3D
inegar is applied to our solid solution (clay body). In the onslaught we ma=
=3D
y even find some of the alkali metals or our aluminum from the octahedral c=
=3D
lay layer forming soluble alkali metal salts of acetic acid and other compo=
=3D
unds, some acidic, some basic (these may deposit on clay surfaces as they d=
=3D
ry). We're left with a thin silica gel of sorts. Debris will clog clay pore=
=3D
s. After some time the pores will =3DE2=3D80=3D98flush=3DE2=3D80=3D99 and r=
eopen larger=3D
.=3D20
Vinegar increases the pore size and permeability of a clay body. We may not=
=3D
ice the benefits of increased water content and slightly plumper, more mana=
=3D
geable clay. Some clay researchers wipe their clay body with vinegar just t=
=3D
o increase porosity before running tests. In one study I read, researchers =
=3D
were surprised to find their clay body cavernous in the middle after using =
=3D
dilute acetic acid =3DE2=3D80=3D93 it had settled in an area and opened it =
up. La=3D
ndfill managers worry about the affect of organic acids, acetic acid includ=
=3D
ed, on the integrity of their clay liners and barriers and routinely test f=
=3D
or cracks. So, yes, vinegar affects a clay body but maybe not in the manner=
=3D
we=3DE2=3D80=3D99re accustomed to thinking about it.=3D20
Properly understood there could be many uses for deflocculation-flocculatio=
=3D
n activities by studio potters. It=3DE2=3D80=3D99s just a tad off the beate=
n path=3D
but not beyond the understanding of many of us. I=3DE2=3D80=3D99ve got a f=
ew exp=3D
eriments in mind but vinegar would never be my choice as a clay body additi=
=3D
ve.=3DC2=3DA0=3D20
Marian
Neon-Cat
www.neon-cat.com
Neon-Cat on mon 12 oct 09
Vince wrote:
"I am not sure what you are asking."
Vince, I was asking about reaction mechanisms for the claim that vinegar ac=
ts as a flocculant. Mechanisms show or tell how things do what they do.
Vince wrote: "You say: 'I've always hated the idea of using vinegar in clay=
work.'
Why? Have you physically witnessed how an addition of vinegar can "cure" a
thixotropic claybody? Have you ever done repairs to bone-dry clay with a
paper-clay slip made from powdered claybody, paper pulp, and vinegar? It's =
an amazing experience."
Nope to the first question and no to the second although I saw plenty of aw=
ful results and failures from plain vinegar as a repair aid. Unsightly glaz=
es over injuries after glaze firing, too (mostly clay body discoloration sh=
owing through the glazes or the injury still showing). I have never needed =
a repair aid or joining aid except for once when I snagged a bird wing with=
my sweater vest in newbie clumsiness. I fixed it after bisque and it went =
through a cone 6 glaze firing just fine. I was often called upon to fix fel=
low student fractures and cracks during my abortive couple of classes here.=
I used just 33-35% paper in whatever clay body they were working. Worked g=
reat on dried greenware and quite often on bisqued ware -- I'm a master fix=
er, all without nasty old vinegar:>)
The experience did allow me to design a non-toxic anti-mold/anti-bacterial =
treatment for paperclay, something I have yet to decide what to do with. I =
recently threw out some treated paperclay I'd had for a year and a half or =
more -- pristine stuff but too little to do anything with.
I am glad you are amazed with your vinegar experiences.
It's nice we all get to use those things we like and that work for us. Ther=
e are lots of ways to work in clay.
Besides my 'scientific' reasons for not using vinegar I think it is the sme=
ll that gets me.
Vince wrote: "It sounds like this is a line of scientific inquiry that you =
are primed to delve into."
Primed? More like I shot myself in the foot with this last topic. It was fu=
n to explore and research but involved far too much typing-up for a Monday =
afternoon. Besides it begs further exploration. Next time I'm in the mood t=
o post I'll send in something on the scientific understanding of how pissin=
g in clay really does work. Pretty cut and dried with less typing ... you e=
ver try it?
Marian,
delving back into wet clay work
ivor & olive lewis on mon 12 oct 09
Marian raises two concerns and asks......
1. What do you mean by flocculation.
2. Please explain the mechanism for clay flocculation by vinegar (dilute
acetic acid).
Frank Hamer in his Dictionary 1st Edition covers the second point under the
heading of Flocculation and Flocculants giving equations for the effects of
Hydrochloric acid (p129) and definitions and uses (page 127). Hamer states
that the effect of acetic acid is of short duration.
For an overview of technical and scientific concepts relating to Plasticity
of work done between 1931 and 1957 see E. C. Bloor. "Plasticity: A Critical
Survey" Transactions of the British Ceramic Society. 1957. 56. pp 423-481.
In my opinion these issues can only be addressed if we disregard our
previous learning and preconceptions.
Best regards,
Ivor Lewis,
Redhill,
South Australia
James Freeman on tue 13 oct 09
Hi, Marian...
I believe the article I cited tested all kinds of kaolins and other
materials, not just soda kaolins. It's been several days since I read it,
so perhaps I missed something. Anyway, that was not at all my point in
posting it. You are talking about the electrochemical reactions involved i=
n
flocculation; I, and probably the rest, were ignoring them, and perhaps thi=
s
is the cause of the confusion over the use of vinegar.
The reason I cited the article was because it demonstrated that clay-type
minerals (all of the different things they ran their tests on) flocculate
more readily under lower pH (acidic) conditions than they do in higher pH
conditions, even without the potter possessing a lick of understanding as t=
o
the chemistry involved in the actual flocculation. Are you saying that
vinegar does not lower the pH? If it does lower the pH, then the article
would seem to suggest that the Skittles-magic that causes flocculation can
now operate more efficiently. It seems that the practical effect of the
vinegar (making the slop more acidic) can be used to advantage without any
understanding of just what it is that is causing the flocculation in our no=
w
acidic clay. I don't think potters use vinegar because it is in Hamer, but
rather because it is a non-scary acid that they already have on hand.
For the record, I am not now, nor have I ever been, a flocculator. If I
ever wish to flocculate, rest assured that I would use real, hairy-chested,
alpha-male, MANLY acid, 5 molar stuff that would fry your sinuses as soon a=
s
you popped the cork, not some wimpy salad dressing! (Insert your best Tim
the Tool Man Taylor grunt here)
Take care.
...James
James Freeman
"All I say is by way of discourse, and nothing by way of advice. I should
not speak so boldly if it were my due to be believed."
-Michel de Montaigne
http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/clayart/
On Mon, Oct 12, 2009 at 11:48 PM, Neon-Cat wrote:
>
>
> OK, other than personal experiences I see where some of you are getting
> vinegar as a flocculant.
>
Jess McKenzie on tue 13 oct 09
Neon-Cat wrote, in part:
"I am not sure what you are asking."
Vince, I was asking about reaction mechanisms for the claim
that vinegar acts as a flocculant. Mechanisms show or tell how
things do what they do.
.........................
We're interested in that answer also. No more tap dancing,
please. And, while you're at it, what's the difference--in
effect--between vinegar and, say, Lana's 'magic water'?
Besides pH, of course.
~joan and jess in Sunny Sequim, making plaster bats, nach Jim
Wylder:
http://ceramicartsdaily.org/ceramic-studio-equipment/pottery-
wheels/replaceable-bat-pin-inserts/
marci and rex on tue 13 oct 09
At 10:54 PM 10/12/2009, Neon-Cat wrote:
>page 2
>Properly understood there could be many uses for=3D20
>deflocculation-flocculation activities by studio=3D20
>potters. It=3DE2=3D80=3D99s just a tad off the beaten path=3D20
>but not beyond the understanding of many of us.=3D20
>I=3DE2=3D80=3D99ve got a few experiments in mind but vinegar=3D20
>would never be my choice as a clay body additive.=3DC2
WHEW! And I used to think that working=3D20
with clay wasnt brain surgery !... (GULP !)
Of course, I AM one of those folks who just=3D20
wants to be able to turn the key and drive..not=3D20
have to rebuild an engine..
Marci
www.ppio.com =3D20
Neon-Cat on tue 13 oct 09
Hi James, the date on your study is 1987. Later I'll try to post the list w=
ith the way soil scientists are calculating and thinking about things now, =
in this century.
Sometimes is best to follow a lead on up to the present.
Good effort, though.
What's with all this stuff on manly this and that, James?
You nervous about your show?
What are you wearing? Tux or potter jeans or something in between? Just cur=
ious. I'm sure all will go well.
And gee thanks, Mel, that was a sweet thing to post about science debates -=
- but I really am out of the science mood now. Maybe someone else can jump =
right on in -- the water is fine now.
Marian
Neon-Cat on wed 14 oct 09
That=3DE2=3D80=3D99s OK, Bruce. Lots to think on. All of this is like mind =
candy =3D
to me. All interesting, even divergent opinions.=3D20
But really, clay particles are quite tiny -- less than 2 micrometers (micro=
=3D
ns) or 2 one-thousandths of a millimeter, equivalent spherical diameter, by=
=3D
one definition. Can you see them with the naked eye? I can=3DE2=3D80=3D99t=
. Hair=3D
is about 40-120 microns in diameter. The average limit of resolution for t=
=3D
he human eye is 100 microns. I can see particles, probably books (tactoids)=
=3D
in the terra sig suspensions I have sitting around if I shine a flashlight=
=3D
across the jugs that contain them (Tyndall effect). When working and I get=
=3D
clay on my hands, I bet they=3DE2=3D80=3D99re smeared tactoids, not itty-b=
itty i=3D
ndividual clay particles.=3D20
Would it be bad to have particles, individual or stacked, coating grains of=
=3D
silica? Or feldspar? Or tucked into an organic aggregate? Must we attempt =
=3D
to gather all clay particles more closely together in a clay body? A nice m=
=3D
ix works for me. You might be able to get more aggregation if you work at i=
=3D
t, but like you said, it=3DE2=3D80=3D99s a slow process. If it could be don=
e as y=3D
ou mentioned, what would be the properties of a clay body =3DE2=3D80=3D9Cfl=
occula=3D
ted=3DE2=3D80=3D9D (doctored) in some places and not in others?=3D20
Even in water-clay suspension like slips and glazes I bet we're flocculatin=
=3D
g and deflocculating tactoids based on their net charge (the sum of the sur=
=3D
face charges and edge charges).
And once you got vinegar or something else into your clay body and close to=
=3D
a target you'd still have to get its ions, providing it does dissociate, a=
=3D
dsorbed. Not an easy task -- what's already on the target is firmly bound. =
=3D
It would be sort of like having a quarterback trying to make a last ditched=
=3D
run through a determined line of blockers.=3D20
Ya all have fun, you=3DE2=3D80=3D99ve got my =3DE2=3D80=3D9Ctake=3DE2=3D80=
=3D9D on this and n=3D
o doubt, from time-to-time down the clay path, I=3DE2=3D80=3D99ll revisit t=
he sub=3D
ject. But I don=3DE2=3D80=3D99t now feel the need to mess with my clay bodi=
es any=3D
more than is normal.=3D20
Marian =3D20
--------
Bruce Girrell wrote:=3D20
"First, let me say that I am behind you 100% in putting some science behind=
=3D
"what all experienced potters know". All too often an idea gets propagated=
=3D
simply because some supposedly more learned person said so. But I do have =
=3D
to take issue with your statement above.
No one would dump some vinegar on a mass of clay and expect its properties =
=3D
to change. What actually happens is that the clay body gets a thorough wedg=
=3D
ing after the addition of the vinegar. During that process, the clay partic=
=3D
les _do_have the opportunity to rearrange. The process is much slower than =
=3D
if the acid were to have been added to slip, but is not as outrageous of an=
=3D
idea as the quote above makes it sound."
Neon-Cat on wed 14 oct 09
James, I=3DE2=3D80=3D99m going to stand by what I wrote previously. If you =
want t=3D
o keep on thinking about all this keep in mind we are talking about a clay =
=3D
body not a water-clay suspension. A clay body is a solid solution with wate=
=3D
r and gas phases, where reactions are only possible at the interface betwee=
=3D
n solid-gas and solid-water. I don=3DE2=3D80=3D99t believe a potter or clay=
maker=3D
would ever create conditions that would require a clay body to need to be =
=3D
=3DE2=3D80=3D98flocculated=3DE2=3D80=3D99. The whole concept of =3DE2=3D80=
=3D9Cwell flocculat=3D
ed clay body=3DE2=3D80=3D9D seems to be new, trendy, and totally bogus =3DE=
2=3D80=3D93 =3D
mere hype.=3D20
Once clay is out of colloidal suspension, it=3DE2=3D80=3D99s too late to th=
ink of=3D
changing the surface or edge charges of individual clay particles so we ca=
=3D
n=3DE2=3D80=3D99t flocculate our clay bodies like we might flocculate a sli=
p or g=3D
laze. All talk of pH dependent edge charge (possible only on broken edges o=
=3D
f kaolin anyway and then only at the hydroxyl of the octahedral Al-OH) or n=
=3D
on-pH dependent surface charge and other chatter is moot.=3D20
But to address your concerns since you=3DE2=3D80=3D99ve brought up the 1987=
study=3D
twice -- your study deals with soil, irrigation, and agricultural. The cla=
=3D
ys were Na- or Ca-saturated and freeze-dried before use. They tell you this=
=3D
right up front. This means the researchers took individual kaolin particle=
=3D
s and slapped a sodium ion or two on their negative face. Then, in solution=
=3D
, they messed with edge charges. In my previous post I did mention two sour=
=3D
ces of charge, one, on the kaolin surface that is non-pH dependent due to i=
=3D
somorphic substitution, the other, the edge charges, that are subject to pr=
=3D
otonation and deprotonation reactions, some of which may involve changes in=
=3D
pH. Your vinegar will add its ions to solution if conditions are favorable=
=3D
for its ionization, the odds of which go up with increasing pH. One might =
=3D
say the effectiveness of vinegar is pH dependent. Lots of reactions are pH =
=3D
dependent and kaolinite particles and tactoids are reactants in reactions,
too. They will be affected most at certain pH levels or not at all at othe=
=3D
r pH points. As mentioned before, the point of zero charge (pzc) for kaolin=
=3D
ite is 4.7. This means that when a bathing solution pH is below the pH(pzc)=
=3D
the mineral surface of an individual kaolinite particle will have a net po=
=3D
sitive charge. When the solution pH is greater than the pH(pzc) the kaolini=
=3D
te surface will have a net negative charge. This means that in normal condi=
=3D
tions where we encounter the kaolinite, its low pH(pzc) gives it a greater =
=3D
ability to attract and retain cations over a broad clay pH range than miner=
=3D
als with a higher pH(pzc). Other examples: Quartz (alpha-SiO2) has a pH(pzc=
=3D
) of 2.9; amorphous silica (SiO2.2H2O) like that which might be found in ri=
=3D
ce hull ash, has a pH(pzc) of 3.5. Rutile (TiO2) has a pH(pzc) of 5.8; hema=
=3D
tite (alpha-Fe2O3) has a pH(pzc) of 8.5. This information might be of most =
=3D
importance to those working with water-clay suspensions like glazes
and slips. Overall though, clay tactoids (books or stacks of clay particle=
=3D
s) in a clay body as we encounter them will have a net negative charge sati=
=3D
sfied through the association of cations like Na+, Ca2+, and Mg2+ making th=
=3D
em neutral.=3D20
=3D20
Today soil researchers looking at soils containing high amounts of sodium c=
=3D
all them sodic soils. I mention this because at one point Ron had justified=
=3D
clay body flocculation by mentioning that sodium ions might be being unlea=
=3D
shed into clay bodies from their very own clay body components, primarily f=
=3D
eldspars. Sodic soils are those whose exchange complex (interface between t=
=3D
he solid-solution and the water phase) contains sufficient Na+ to adversely=
=3D
impact soil structure, the soil=3DE2=3D80=3D99s hydraulic properties, and =
plant =3D
growth and development. On the other hand there are soils called saline and=
=3D
saline soils are those containing an abundance of soluble salts, not just =
=3D
sodium. Common salts present in the water-phase of salt affected soils incl=
=3D
ude the base cations (nonhydrolysing cations) Ca2+, Mg2+, Na+, K+, and the =
=3D
anions Cl-, SO42-, HCO3- and CO32-, and NO3-. These days a soil is deemed s=
=3D
aline if its electrical conductivity exceeds 4 dS m-1 (where dS is
decisiemens and where seimen is the SI units of conductance) and sodic if =
=3D
the exchangeable sodium percent (ESP) is greater than 15. Sodic and saline =
=3D
soils are often the result of poor irrigation practices in agriculture and =
=3D
natural conditions. If we want to move along and talk about clay, sodic soi=
=3D
ls (the =3DE2=3D80=3D9Cbad=3DE2=3D80=3D9D soils) cause swelling and dispers=
ion of the c=3D
lay minerals they contain. Clays most involved in swelling are those in the=
=3D
smectite group =3DE2=3D80=3D93 we are familiar with the montmorillonite sp=
ecies =3D
of clays that include bentonite. Our kaolin may disperse but it can=3DE2=3D=
80=3D
=3D99t swell.=3D20
Dispersive soils are those that disperse spontaneously without mechanical s=
=3D
tress. In soils we are dealing with the dispersion of clay tactoids, not in=
=3D
dividual clay particles, and this is due to mutual repulsion of tactoids. D=
=3D
ispersion is exacerbated by low electrolyte concentration. Tactoids break d=
=3D
own completely when the ESP is around 50 causing soils to degrade and becom=
=3D
e unstable. [continue to next post]
Neon-Cat on wed 14 oct 09
page2
Saline soils are non-dispersive soils and are what we might think of as flo=
=3D
cculated soils although soil scientists usually reserve the terms flocculat=
=3D
ed and flocculation for processes in suspensions. To remain saline the soil=
=3D
s must have a sufficient concentration of electrolytes. In soil science col=
=3D
loidal solutions flocculate because electrostatic repulsive and solvation f=
=3D
orces are balanced by van der Waals attractive forces that operate between =
=3D
adjacent particles. Solvation forces are those required to remove the water=
=3D
s of hydration from counterions (also called exchangeable cations =3DE2=3D8=
0=3D93=3D
they=3DE2=3D80=3D99re those cations that surround the tactoids). This occu=
rs onl=3D
y when the double layers surrounding the particles are compressed enough to=
=3D
permit the particles to approach each other and for the attractive forces =
=3D
to then overcome the repulsive forces. Double layers (also called diffuse l=
=3D
ayers) are most compressed when the soil solution bathing and saturating ou=
=3D
r
little clay particles contains divalent or trivalent ions and/or the elect=
=3D
rolyte solution is concentrated. They are twice as thick when the saturatin=
=3D
g cation is monovalent and/or the concentration of electrolytes in the bath=
=3D
ing solution is dilute. In these conditions the double layer surrounding th=
=3D
e particles will overlap, causing electrostatic repulsive forces between th=
=3D
e particles that results in dispersion (deflocculation).=3D20
At any rate, critical coagulation concentration (CCC), also called the crit=
=3D
ical flocculation concentration, is dependent on the nature of the minerals=
=3D
in a colloidal suspension and on the composition of the electrolyte soluti=
=3D
on. Flocculation equations for suspensions do show that the concentration o=
=3D
f a monovalent electrolyte suspension must be 64 times that of a divalent e=
=3D
lectrolyte suspension to cause flocculation. The CCC for kaolinite systems =
=3D
containing Na+ averages about 8.5mM while one containing Ca2+ averages 0.2m=
=3D
M at pH 7-8.3. You will note that the lowly H+ ion is not mentioned as an e=
=3D
xchangeable cation in these processes =3DE2=3D80=3D93 it=3DE2=3D80=3D99s to=
o wimpy. It =3D
may, along with the CH3COO- anion from vinegar add to the total electrolyte=
=3D
concentration overall if you just feel you must use vinegar but this contr=
=3D
ibution will be pH dependent and it will take far more vinegar than a compo=
=3D
und capable of ionizing and releasing divalent or trivalent cations. Couple
vinegar with HCl and the HCl, a strong acid, will inhibit the release of a=
=3D
ny H+ from the vinegar (this would be in low pH conditions). Put vinegar in=
=3D
a clay body, especially a slightly dehydrated clay body, and the pH of vin=
=3D
egar itself may increase:=3D20
CH3COO- (aq) + H2O <---> CH3COOH (aq) + OH- (aq).=3D20
If anything, adding an acetic acid or a weak acid source like wine would ca=
=3D
use chemical weathering of clay body components, the clay(s) included. We=
=3D
=3DE2=3D80=3D99d be liable to get Na+, K+, and other goodies released into =
the so=3D
il exchange complex. Increased electrolyte concentration would then make th=
=3D
e clay body more saline for a naturally perfect clay body. One could even a=
=3D
dd sodium as table salt, up to a point, to increase electrolyte concentrati=
=3D
on in the clay body water phase. Vinegar and other weak organic acids may a=
=3D
lso aid anaerobic decomposition or be decomposed themselves by methanogenic=
=3D
bacteria to produce hydrogen (H2), methane (CH4, natural gas), carbon mono=
=3D
xide (CO), carbon dioxide (CO2), and polycarboxylic acids.=3D20
In my native clay bodies I add 3-5% salt (NaCl) by dry weight of clay and b=
=3D
ecause my clay bodies contain high amounts of calcium carbonate anyway, I=
=3D
=3DE2=3D80=3D99ve got a good saline (non-dispersive) clay body. Sometimes I=
make =3D
soluble calcium chloride in the clay body by the addition of acids and this=
=3D
is another good source of Ca2+ cations. In a standard clay body what are t=
=3D
he chances of having huge amounts of sodium release from the spar?
A sodic, dispersive, swelling clay body, one with too many sodium ions migh=
=3D
t possibly be found if you mined your clay out of a salt marsh, an arid des=
=3D
ert environment, a boggy environment where the clay contains a high degree =
=3D
of organics, or a place where clay sulfur content runs very high. In a typi=
=3D
cal studio pottery environment I just don=3DE2=3D80=3D99t see a clay body e=
ver ne=3D
eding to be treated because it has become sodic with the passage of time or=
=3D
arrives that way from the ceramic supply store.=3D20
So why talk of flocculating clay bodies? We should rather adjust our clay b=
=3D
ody consistency to our liking (plasticity is included as one of the physica=
=3D
l properties of clay as grouped under a heading called consistency) and use=
=3D
proper terminology when talking about the processes we used. It will put u=
=3D
s all on the same page and in the long run be a help to those clay workers =
=3D
who might wish to investigate clay science further or keep current with res=
=3D
earch in allied fields. We learn new words, processes, and techniques all t=
=3D
he time, so what=3DE2=3D80=3D99s a few more words and terms for studio pott=
ers? W=3D
ould it be too much to ask authors and educators to be mindful of terms the=
=3D
y use? I think not. =3D20
Marian=3D20
Neon-Cat=3D20
www.neon-cat.com=3DC2=3DA0
Bruce Girrell on wed 14 oct 09
Neon-Cat wrote:
"Once clay is out of colloidal suspension, it's too late to think of changi=
=3D
ng the surface or edge charges of individual clay particles so we can't flo=
=3D
cculate our clay bodies like we might flocculate a slip or glaze."
Marian,
First, let me say that I am behind you 100% in putting some science behind =
=3D
"what all experienced potters know". All too often an idea gets propagated =
=3D
simply because some supposedly more learned person said so. But I do have t=
=3D
o take issue with your statement above.
No one would dump some vinegar on a mass of clay and expect its properties =
=3D
to change. What actually happens is that the clay body gets a thorough wedg=
=3D
ing after the addition of the vinegar. During that process, the clay partic=
=3D
les _do_ have the opportunity to rearrange. The process is much slower than=
=3D
if the acid were to have been added to slip, but is not as outrageous of a=
=3D
n idea as the quote above makes it sound.
Bruce Girrell
Sofia Ivanov on wed 14 oct 09
Dear neoncat,
Why do you do this to us? You asked in a provocative way how can vinegar
cause flocculation (prove it to me, fingers on chalk board). You received
an answer supported by scientific citation that it does so by increasing
acid of clay and more acid of clay promotes flocculation.
Instead of saying sorry, i was so caught in looking for a deep chemistry
answer that I completely missed the obvious simple answer, instead you just
dismiss the science report because it is 20 years ago. So in 20 years
behavior of acid has changed? in 20 years particles stopped flocculating
more readily in acidic?
Now you give us 2 pages of post saying ok, vinegar can help flocculation al=
l
these differnet ways, but there are better things to use, and you hide this
confession deep inside lots of talk of ions and divalent charges. Not the
same as does not work.
I am back to lurker, so don't send me please 2 more pages of ions and
divalent charges.
Jess McKenzie on wed 14 oct 09
neon Cat wrote, in part:
... At any rate, critical coagulation concentration (CCC),
also called the critical flocculation concentration, is
dependent on the nature of the minerals in a colloidal
suspension and on the composition of the electrolyte solution.
Flocculation equations for suspensions do show that the
concentration of a monovalent electrolyte suspension must be
64 times that of a divalent electrolyte suspension to cause
flocculation. The CCC for kaolinite systems containing Na+
averages about 8.5mM while one containing Ca2+ averages 0.2mM
at pH 7-8.3. You will note that the lowly H+ ion is not
mentioned as an exchangeable cation in these processes - it=3DB4s
too wimpy. It may, along with the CH3COO- anion from vinegar
add to the total electrolyte concentration overall if you just
feel you must use vinegar but this contribution will be pH
dependent and it will take far more vinegar than a compound
capable of ionizing and releasing divalent or trivalent
cations. ...
So, after all, it's chemistry, not alchemy. Well done,
Marian!
Pottery clay is a colloid. As my old physical chemistry text
(Glasstone) points out, "flocculation" (synonyms:
precipitation, coagulation) occurs when a "visible *solid* is
produced (from a colloid) by various means, e.g., addition of
electrolyte, evaporation, or cooling. BTW, the grand old man
of colloid chemistry, Graham (of cracker fame) called it
"pectinization." We still use the term in jam and jelly
making.
I should point out that not all colloids "floc" at a given
ionic strength. Back in the good old days we fractionated
blood plasma (a collodal system) into its components (e.g.
albumin) by titrating with ammonium sulfate, ice cold, of
course.
Other examples come to mind. Oil patchers on the list know
what happens to drilling mud (clay) when you hit a layer of
brine.
In brief: Flocculation occurs when the clay's environment
reaches a certain ionic strength. Ionic strength depends on
two factors: (1) the molar concentration of each ion, and (2)
its valence. Ron Roy, in an off-list msg to me, pointed out
that epsom salts (MgSO(4)) is his salt of choice for producing
flocculation. Magnesium has two valence electrons, so mol for
mol its ionic strength is greater than, say, sodium ion, as
Marian says. True, in solution MgSO(4) is slightly acidic,
but, as she points out, it may be ionic strength, not pH, that
does the flocculating.
Another thought: Oddly enough, we know the value of
*de*flocculated clay, e.g. in slip-casting, but, we beginners
on the list have yet to discover what's so great about
flocculated clay. We leave that explication to the pottery
experts.
~jess (Joan's in FL)
Jess McKenzie on thu 15 oct 09
Vince, you continue to peak our newbie interest, but we're
still missing some information: Just what does your
experience tell you about the *practical* effects of vinegar
and epsom salts in pottery; i.e., how do they help you make
pots? Feel free to avoid scientific explanation.
~joan and jess in Sequim
Vince Pitelka wrote, in part:
... scientific explanation is not my department. ... I work
primarily from practical studio experience, and I know from
experience all about the practical effects of Epsom salts or
vinegar on the plasticity and performance of claybodies. ...
ivor & olive lewis on thu 15 oct 09
Dear Jess McKenzie,
You ask <<...And, while you're at it, what's the difference--in
effect--between vinegar and, say, Lana's 'magic water'? Besides pH, of
course ...>>
Lana's 'magic water' is used with leather hard clay as an adhesive. Used i=
n
small quantities it has a "Deflocculating" effect at the surface of the cla=
y
and enables the two parts to "Marry".
Best regards,
Ivor Lewis,
Redhill,
South Australia
Jess McKenzie on thu 15 oct 09
Thanks, Ivor. The effects we're getting in our experiments
here are quite consistent with your explanation:
1. Magic water water had little effect on fresh clay--it is
adequately de-flocculated as it is.
2. As expected, we found no effect with bone-dry material.
Paper clay works well though. We made the paper clay using
magic water, but we suspect plain water would serve as well.
3. But we saw a nice glue effect using magic water only on
leather-hard pieces.
As another msg states, we have turned to our own technical
library, and we've found some interesting information, also
consistent with the info you and Neon-Cat have submitted.
We sent a msg on that yesterday.
~joan and jess
Date sent: Thu, 15 Oct 2009 11:31:40 +1030
You ask <<...And, while you're at it, what's the difference--
in effect--between vinegar and, say, Lana's 'magic water'?
Besides pH, of course ...>>
Lana's 'magic water' is used with leather hard clay as an
adhesive. Used in small quantities it has a "Deflocculating"
effect at the surface of the clay and enables the two parts to
"Marry".
Best regards,
Ivor Lewis,
Redhill,
South Australia
Vince Pitelka on fri 16 oct 09
This will be my last post on this subject. When we add a little vinegar to
a thixotropic claybody, it becomes plastic and workable. If we add Epsom
salts when mixing a claybody that contains a soda spar, it takes longer
before the spar releases enough soluble alkali to cause the claybody to
become thixotropic. When we add vinegar to a claybody, it makes the clay
"stickier" and more structurally stable, as if the particles are attracting
one another and thus increasing contact friction. Adding vinegar or Epsom
salts seems to have an effect very similar to what happens when you add a
flocculant to a slip. When we add a soluble alkali to a workable claybody,
it becomes unworkable and thixotropic, as if the particles are repelling on=
e
another and thus the water layers between particles are maximized and the
friction that provides structural stability is reduced. Adding an alkali t=
o
a claybody seems to have an effect very similar to what happens when you ad=
d
a deflocculant to a slip. For over a decade we have been referring to thes=
e
processes in clay as flocculation and deflocculation, for the simple reason
that the behavior is virtually identical to what happens with a true water
suspension. That still works fine for me. Marian, you are correct that I
support the correct use of ceramic terminology, and when someone proves to
me that the terms flocculation and deflocculation are not applicable to
these phenomena in claybodies, and offers me a set of more accurate terms, =
I
will be glad to "correct" my usage. Until then, I see no reason why we
should not continue to use the terms "flocculation" and "deflocculation" in
regard to claybodies when we all understand clearly what we are talking
about in the usage of these terms.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
Neon-Cat on fri 16 oct 09
Dear Vince,
If you all like using vinegar to enhance performance of your clay bodies, w=
hy not? I don't have a problem with that. My quibble was with the years of =
statements on clayart along the lines of "vinegar is a flocculant".
I liked the point Paul Herman brought up (Re: An offer of cream to Neon-cat=
) about what to call these enhancement effects, enhancers, or the enhanceme=
nt process. Doping? Something else? Back to flocculant and flocculation? Be=
ats me. Mel's 'fertilize and energize' is kind of catchy.
And Paul's other point was valid, too -- I handbuild and have, most of this=
year, been using truly odd clay bodies that the wheel-throwing majority wo=
uld hate. Fat or lean, or totally strange clay, it doesn't make much differ=
ence to me.
I work from home, have no real studio, few resources, and certainly no lab.=
Suggest all you want, it would be utterly unfeasible for me at this time t=
o undertake meaningful experiments. Besides, I am trying to learn to work c=
lay and become good at clay art and clay craft. It would not be a good use =
of my time now to mess with hands-on exploration into the nature of vinegar=
as a clay body addition. Two-to-one, even should I devote my life to this =
undertaking it would receive little or no attention within the clay communi=
ty or be called into question for want of fancy initials attached to my nam=
e or for some other reason. Lose-lose for me.
So, call it what you will. As potters on clayart did we ever even come to a=
consensus on a definition for plasticity? It seems me it has become a popu=
lar catch-all term these days.
What I hear is a dodge, Vince. And a pretty good one from your point of vie=
w -- you don't care and don't wish to be bothered. Vinegar works for you. Y=
ou have a name for your 'vinegarization process' that you have been using a=
nd are happy with, so why change? But tell me, why do we spend so much time=
discussing the meaning of terms on clayart? Why concern ourselves with his=
torical perspective either, for that matter? The current thread on porcelai=
n and bone china being a good example. Are you now implying that we embrace=
an 'anything goes attitude'? That would seem like somewhat of a reversal o=
n your part since I've read quite a number of posts from you where you did =
argue for meaning and preciseness and certain very specific right and wrong=
methods regarding technique, tools, kilns, definitions, etc. You have just=
been asking about a few differences in the temperature hardening plaster c=
an reach. Why? Just passing the time on-line making chit-chat?
The idea of studio art as lawless has a certain liberating appeal. It does =
make communication somewhat problematic and I can't imagine continuity in f=
ormal education in the arts in this climate. If tomorrow I begin to refer t=
o my native clays as porcelain and say my electric kiln is firing in reduct=
ion, how will the list understand me? Or does that no longer matter?
Potters will always find a way to make pots if they've got that urge. And t=
hat's of some comfort to me in this small niche we call studio pottery.
So, it's back to gathering practical experience for me -- now fully a law u=
nto myself. No concerns whether what I do is art or craft or whether any of=
it makes a wit of sense to others -- freedom, what an exhilarating feeling=
!
Did someone lose fingers? Quite a practical lesson, one the student won't s=
oon forget. Someone should have said something? Why? In this day and age ga=
rnering practical experience seems to be the trend although it may not be w=
ithout a certain amount of howling in the desert.
Marian
Vince wrote: "Marian -
You have to realize that I have no need or incentive to "present my case," =
because the scientific explanation is not my department. I don't care that =
you are challenging the truth of flocculation and deflocculation in claybod=
ies. I work primarily from practical studio experience, and I know from exp=
erience all about the practical effects of Epsom salts or vinegar on the pl=
asticity and performance of claybodies. If someone else wants to do scienti=
fic experiments to explore the "mechanism" of flocculation and deflocculati=
on in claybodies, I'll be interested in the results. Marian, if you are so =
interested in this, why don't you undertake the experiments? I suggested th=
at before. With your scientific knowledge you are far better equipped to do=
so than I am.
- Vince"
ivor & olive lewis on sun 18 oct 09
Dear Vince Pitelka,
Recent discussion on this topic makes me wonder if we are in a semantic
mobius loop.
It seems to be common knowledge, derived from the records of Daniel Rhodes,
Frank Hamer and others, that clay recipes prepared for slip casting should
incorporate a compound described as a Deflocculant. From that I seem to hav=
e
drawn an erroneous conclusion that when a clay body does not contain a
deflocculant the plastic mass we are working with must be in a flocculated
state. This is concept is supported by Hamer. Rhodes supports flocculants
only in the context of Glazes.
One thing always mystifies me. It concerns the proportions of clay, other
minerals and water in a plastic body. We are so used to considering these
ingredients in terms of Mass (aka Kg or Lbs weight) and totally disregard
the volume (litres, millilitres, pints and fluid ounces) of each ingredient
in our scientific discussions. Comparative results are a mystery to explain
! !
For example, if the additional sand and felspar are ignored and we use only
water and either a ball clay or kaolin powder which has 70 percent mass of
solids and 30 per cent mass of water and convert these values to volumetric
measure there is about equal proportions of space occupied by each
ingredient in the resultant mass. From this result it seems that each flake
of clay crystal is separated from its neighbours by a layer of water equal
in thickness to the flakes of clay.
When I mix the same masses of Water and Sand (Actually, Sillimanite which
was handy but has a density almost equal to that of clay) the mixture
separates and there is a distinct layer of almost clear water above the
sediment.
If your University has an Environmental Scanning Electron Microscope I woul=
d
be willing to provide samples for testing.
I would agree with you that there has to be consistency between terminology
and context.
Best regards,
Ivor Lewis,
Redhill,
South Australia
Vince Pitelka on sun 18 oct 09
Ivor Lewis wrote:
"For example, if the additional sand and felspar are ignored and we use onl=
y
water and either a ball clay or kaolin powder which has 70 percent mass of
solids and 30 per cent mass of water and convert these values to volumetric
measure there is about equal proportions of space occupied by each
ingredient in the resultant mass. From this result it seems that each flake
of clay crystal is separated from its neighbours by a layer of water equal
in thickness to the flakes of clay."
Ivor -
Unfortunately I do not have access to an electron microscope. But I will
brag and tell you that my mother Dorothy Pitelka was the first person in th=
e
western US trained in the use of an electron microscope. UC Berkeley flew
her to the Siemens factory in Germany for the training.
Regarding your description above, I do understand your point. I think that
the reality is that a good part of the water is in cavities between
irregular particles, rather than what we might envision in a perfect model
as even layers of water. I always talk to my students about the "water of
plasticity" - the amount of water required to achieve plasticity with each
different clay or claybody sample. Of course the finer the clay particles,
the more water required to reach the plastic state, the more plastic the
resulting clay, and the higher the drying shrinkage. As a demonstration of
the amount of water that can be absorbed by clay, I place about an inch of
dry bentonite in the bottom of a small yogurt container and add about an
equal volume of water. Over the next few hours the bentonite swells up to
fill most of the container as a fairly dense mass. If you add more water,
it overflows the container as a slurry. Then the students get to feel its
consistency, and of course pure bentonite mixed with water produces the mos=
t
deliciously slippery substance in existence. And then we spread the
bentonite slurry on a pan and let it dry, and it forms the classic "popcorn=
"
shape caused by the extreme shrinkage.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
paul gerhold on mon 19 oct 09
"OF course the finer the clay particles the more water required to reach th=
e
plastic state" This would not seem to be self evident to me. Can you
explain the reason?
Paul
On Sun, Oct 18, 2009 at 11:11 AM, Vince Pitelka wrote=
:
> Ivor Lewis wrote:
> "For example, if the additional sand and felspar are ignored and we use
> only
> water and either a ball clay or kaolin powder which has 70 percent mass o=
f
> solids and 30 per cent mass of water and convert these values to volumetr=
ic
> measure there is about equal proportions of space occupied by each
> ingredient in the resultant mass. From this result it seems that each fla=
ke
> of clay crystal is separated from its neighbours by a layer of water equa=
l
> in thickness to the flakes of clay."
>
> Ivor -
> Unfortunately I do not have access to an electron microscope. But I will
> brag and tell you that my mother Dorothy Pitelka was the first person in
> the
> western US trained in the use of an electron microscope. UC Berkeley fle=
w
> her to the Siemens factory in Germany for the training.
>
> Regarding your description above, I do understand your point. I think th=
at
> the reality is that a good part of the water is in cavities between
> irregular particles, rather than what we might envision in a perfect mode=
l
> as even layers of water. I always talk to my students about the "water o=
f
> plasticity" - the amount of water required to achieve plasticity with eac=
h
> different clay or claybody sample. Of course the finer the clay particle=
s,
> the more water required to reach the plastic state, the more plastic the
> resulting clay, and the higher the drying shrinkage. As a demonstration =
of
> the amount of water that can be absorbed by clay, I place about an inch o=
f
> dry bentonite in the bottom of a small yogurt container and add about an
> equal volume of water. Over the next few hours the bentonite swells up t=
o
> fill most of the container as a fairly dense mass. If you add more water=
,
> it overflows the container as a slurry. Then the students get to feel it=
s
> consistency, and of course pure bentonite mixed with water produces the
> most
> deliciously slippery substance in existence. And then we spread the
> bentonite slurry on a pan and let it dry, and it forms the classic
> "popcorn"
> shape caused by the extreme shrinkage.
> - Vince
>
> Vince Pitelka
> Appalachian Center for Craft
> Tennessee Tech University
> vpitelka@dtccom.net; wpitelka@tntech.edu
> http://iweb.tntech.edu/wpitelka
>
Snail Scott on mon 19 oct 09
On Oct 19, 2009, at 9:02 AM, Vince Pitelka wrote:
> I wrote:
> "Of course the finer the clay particles the more water required to
> reach the
> plastic state"
>
> Paul Gerhold wrote:
> "This would not seem to be self evident to me. Can you explain the
> reason?"
>
> Hi Paul -
> This is fundamental theory of clay plasticity, and I expect you
> already know
> most of this. The finer the particles, the more water layers needed to
> mobilize the mass and reach a plastic state - the so-called "water of
> plasticity." Of course that's also the reason that clays featuring
> very fine
> particles shrink so much in drying - there is more water to
> evaporate...
A corollary to Vince's statement (not reproduced here in
full) referring to 'green packing'; and the need for varied
particle sizes: I suspect that it is an essential aspect to
this idea that fine-grained clays have more water layers
than coarse ones. If a clay were only composed of coarse
particles, the spaces between grains would be larger than
between the fine particles, and the result might actually be
the opposite. (How much water will a jar of sand hold at
saturation, relative to a jar of slip? Anyone wanna test?)
No actual clay bodies are made this way, however. They
do indeed have varied sizes, with some particles as fine
as the fine-grained clay, which fill the interstices of the
clay body and reduce the water spaces to something
comparable to the size of those in the fine-grained clay,
but with fewer of those spaces due to the inclusion of big
honkin' fireclay particles or grog bits like nuts in the
nougat.
-Snail
Vince Pitelka on mon 19 oct 09
I wrote:
"Of course the finer the clay particles the more water required to reach th=
e
plastic state"
Paul Gerhold wrote:
"This would not seem to be self evident to me. Can you explain the reason?=
"
Hi Paul -
This is fundamental theory of clay plasticity, and I expect you already kno=
w
most of this. The finer the particles, the more water layers needed to
mobilize the mass and reach a plastic state - the so-called "water of
plasticity." Of course that's also the reason that clays featuring very fin=
e
particles shrink so much in drying - there is more water to evaporate.
That's why we normally do not make a claybody with too much ball clay or
bentonite in it - the drying shrinkage would be excessive and would result
in serious cracking.
Plasticity results from the nature of the clay particle - it's flat shape,
ultra-fine size (one cubic inch of clay contains at least five trillion
particles), and affinity for water, and of course involves a balance betwee=
n
the water layers providing lubrication, and the contact points creating
friction that provides working structure. Too much water, and there is too
little friction and poor working structure. Too little water, and there is
too much friction and not enough lubrication to achieve plasticity.
This relates directly to the recent discussion of "green packing," which I
have always referred to as the "distribution of particle sizes." If you
modify a claybody to increase the distribution of clay particle sizes, you
1) maintain the water layers that create plasticity, 2) reduce the overall
water content because there will be less large water-filled voids that do
not contribute to plasticity, 3) increase the number of contact points
between particles and thus increase working structure, 4) decrease firing
shrinkage by eliminating the large voids, 5) increase dry and bisque
strength because of the increased number of contact points between
particles. It's a win-win situation.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
ivor & olive lewis on tue 20 oct 09
Dear Paul,
You ask..."OF course the finer the clay particles the more water required t=
o
reach the plastic state" This would not seem to be self evident to me. Ca=
n
you
explain the reason? >>
The argument is that the smaller the particles in a given mass of compound
the greater the sum of the surface areas of the individual particles. More
surface area adsorbs more water
I am not sure that this is correct. Plasticity can occur within a range of
plus 20% water to less than 30% water. Below 20% water the mixture becomes
"Short" and is difficult to work. Above 30% the mixture becomes "sticky" an=
d
changes into a fluid slip.
Best regards,
Ivor Lewis,
Redhill,
South Australia
Vince Pitelka on tue 20 oct 09
Ivor Lewis wrote:
"The argument is that the smaller the particles in a given mass of compound
the greater the sum of the surface areas of the individual particles. More
surface area adsorbs more water
I am not sure that this is correct. Plasticity can occur within a range of
plus 20% water to less than 30% water. Below 20% water the mixture becomes
"Short" and is difficult to work. Above 30% the mixture becomes "sticky" an=
d
changes into a fluid slip."
Ivor -
I do not get your reasoning. A claybody that has a higher fraction of fine
clay particles will take more water to reach plastic consistency. Within a
certain range, that claybody can be mixed dry or wet, as you mention. A
claybody that has a higher fraction of coarse particles will take less wate=
r
to reach plastic consistency, and again within a certain range, that
claybody can be mixed dry or wet. The range for the second claybody would
be a lower percentage range than for the first. Isn't this just stating th=
e
obvious?
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
ivor & olive lewis on wed 21 oct 09
Dear Snail Scott,
I have in front of me on the desk a jar containing 70 grams (26.9 cu cm) of
Sillimanite sand and 30 grams (30 cu cm)of water. (These are quantities of
water and kaolin in the containers displayed in Mels site.)The Sillimanite
has all settled. Above the sediment is a layer of water about 5 mm deep.
In my clay/water mixtures (70/30 by mass but 26.9/30 by volume)there is no
free water to be found. When the specimen is trowelled out of the container
it is a plastic solid, a little on the sticky side.
You must look at those images to gain an understanding. Or better still,
weigh out a sample of water and sift the weighed clay powder onto the
surface of the water. Adding the water to the clay and stirring reveals no
information.
Best regards,
Ivor Lewis,
Redhill,
South Australia
ivor & olive lewis on wed 21 oct 09
<fine
clay particles will take more water to reach plastic consistency. Within a
certain range, that claybody can be mixed dry or wet, as you mention. A
claybody that has a higher fraction of coarse particles will take less wate=
r
to reach plastic consistency, and again within a certain range, that
claybody can be mixed dry or wet. The range for the second claybody would
be a lower percentage range than for the first. Isn't this just stating th=
e
obvious?>>
Dear Vince Pitelka,
Yes it is stating the obvious. What would not be obvious would be the
difference in Workability.
By the way, I must try your experiment with Bentonite. Sounds interesting.
Best regards,
Ivor
Snail Scott on wed 21 oct 09
On Oct 21, 2009, at 12:52 AM, ivor & olive lewis wrote:
> I have in front of me on the desk a jar containing 70 grams (26.9 cu
> cm) of
> Sillimanite sand and 30 grams (30 cu cm)of water...
> Above the sediment is a layer of water about 5 mm deep.
> In my clay/water mixtures (70/30 by mass but 26.9/30 by volume)there
> is no
> free water to be found...
Cool! Thanks, Ivor!
(I love actual data, even if the
immediate relevance is unclear.
-Snail
Jess McKenzie on wed 21 oct 09
If you'd like something to "play" with, visit a water well
driller and ask for a sample of drilling mud. It's used to
"maintain circulation" and pick up "cuttings." Ask the
driller about it. Most of them love to talk.
Have fun...~jess, and old shooter's helper.
ivor & olive lewis on thu 22 oct 09
Dear Snail,
In your post in Digest 294 you asked the question ........
<<(How much water will a jar of sand hold at saturation, relative to a jar
of slip? Anyone wanna test?)>>
Water drains quickly from sand. if there is an excess of water in the
mixture the sand settles as a sediment leaving excess water above the sand
surface.
The best I have read from the middle of the 20th Cent about the nature of
clays and their behaviour with water would be Ralph E. Grim, " Clay
Mineralogy" Pub McGraw Hill.
There is evidence, if you would wish to search for it, that the water in a
plastic Kaolin based clay body is a structured solid. If this is comparable
to ice in its structure and behaviour then it sheds a bight light on the
nature of the de-airing process. It also helps to explain what happens and
where the gas comes from. It also means that Plasticity can be explained in
a way that is compatible with General Principles of Material Science.
Sincere regards,
Ivor Lewis,
Redhill,
South Australia
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