tim knick on sun 5 mar 06
Why do I have so much trouble joining porcelain? Even if it is wetter than
leather hard, it still cracks. I have tried wetting and scoring. i have
tried smearing slip and scoring. I do not have this problem with a grogged
stoneware. Any helpful hints out there?
Thanks,
Tim
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John Britt on sun 5 mar 06
Tim,
Try deflocculating some slip. (add Darvan 7 to it.)
It works wonders.
Hope it helps,
John Britt
www.johnbrittpottery.com
Marcia Selsor on sun 5 mar 06
Try mixing a paper patch for slip for joining. Use some of your
porcelain, add toilet paper after soaking it overnight,
add a drop of sodium silicate. Mix in a blender.
Marcia Selsor
On Mar 5, 2006, at 11:14 AM, tim knick wrote:
> Why do I have so much trouble joining porcelain? Even if it is
> wetter than
> leather hard, it still cracks. I have tried wetting and scoring.
> i have
> tried smearing slip and scoring. I do not have this problem with a
> grogged
> stoneware. Any helpful hints out there?
> Thanks,
> Tim
>
> ________
Michael Wendt on sun 5 mar 06
Tim,
I can't speak for all porcelains but the one I make
from Helmer Kaolin is strong, reliable and easy to
join in almost any stage if you forget the slip and
score method. I make the handles after the mugs are
leather hard and already trimmed, place them on a fan
and monitor the drying until they are just barely
leather.
I carve the handles to fit the shape without any gaps,
put one or two drops of water on the mating surface,
scrub lightly with a tooth brush to make a marking
slip.
The handle is then touched lightly to the cup to mark
position. A drop of water is placed at each location,
the handle is placed and wiggled to snug it until it
won't
move. The joints are then radiused with a pin tool
handle
to eliminate the tendency to crack due to the tiny bit
of
wetter material left there.
Try it and see if it works for you.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Tim wrote:
Why do I have so much trouble joining porcelain? Even
if it is wetter than
leather hard, it still cracks. I have tried wetting
and scoring. i have
tried smearing slip and scoring. I do not have this
problem with a grogged
stoneware. Any helpful hints out there?
Thanks,
Tim
Don Goodrich on sun 5 mar 06
Tim,
Try joining without scoring. As Nils Lou points out in
the February Ceramics Monthly (page 96), scoring just
introduces air pockets that negate the intimate contact
that you're trying to achieve between clay particles.
In porcelain especially, with no grog to get in the way,
the material is just a collection of flat platelets that
are happy to stick together the way they are. Why rough
them up? If you need to fill minor gaps between joined
surfaces, brush slip thickened to the consistency of
library paste (anybody remember that from grade school?)
on the joint surfaces before joining. However, joining
smooth porcelain parts can often be done with nothing
more than water.
Tom Coleman made these points at a workshop I attended
a few years ago. I went back to my studio and tried it.
Danged if he wasn't right.
If you're plagued by attachments like handles pulling
loose as they dry, it may be due to their shape allowing
them to dry faster than the rest of the pot. Keep the
handle covered so it dries last, and see if that helps.
Good luck,
Don Goodrich
goodrichdn@aol.com
On Sun, 5 Mar 2006 12:14:55 -0600, tim knick
wrote:
>Why do I have so much trouble joining porcelain? Even if it is wetter than
>leather hard, it still cracks. I have tried wetting and scoring. i have
>tried smearing slip and scoring. I do not have this problem with a grogged
>stoneware. Any helpful hints out there?
>Thanks,
>Tim
Dick & Mary Walker on sun 5 mar 06
You might try adding a little sodium silicate to your slip. That should strengthen your attachment assuming the cracking or separating is at the joint. An eye dropper (small) to around one pint of slip should be enough. Also be sure that the two pieces you are joining are at approximately the same degree of wetness/dryness, press the seams together tightly so much of the slip you use to join is pressed out, and dry slowly and evenly.
Good luck
>From: tim knick
>Date: Sun Mar 05 12:14:55 CST 2006
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: joining porcelain
>Why do I have so much trouble joining porcelain? Even if it is wetter than
>leather hard, it still cracks. I have tried wetting and scoring. i have
>tried smearing slip and scoring. I do not have this problem with a grogged
>stoneware. Any helpful hints out there?
>Thanks,
>Tim
>
>_________________________________________________________________
>Express yourself instantly with MSN Messenger! Download today - it's FREE!
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>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.
Peter Cunicelli on sun 5 mar 06
Hey Tim,
I've had these problems in the past as well.
Some things I've learned are:
Use reinforcement coils at the joins. This really helped a lot. I also
paddle all my joins with a piece of wood. It's really important that you
press the coil into the join so that there's no air bubbles. That can be
ugly.
Bevel the two pieces that are to be joined in order to make the join
stronger.
Score deeply and close together.
Use a really thick slurry.
Porcelain has to be dried very, very slowly. When I finish a piece, I
cover it lightly with plastic and let it sit for a day to as long as a
week. Most of my work is very dry when I'm finished with it anyway.
I've also found that burnishing helps a lot.
Recently, I've been taking a class in paper clay. All of the above,
apparently, are no longer applicable. I don't score the joins. I use
water, not slurry. I do paddle and bevel, however. I did make a few
pieces with paper clay and they made it all the way through the glaze
firing without any of the big issues you seem to be having. I'm pretty
sure I'm a paper clay convert now.
Hope this helps.
Peter
(www.petercunicelli.com)
tim knick on sun 5 mar 06
Thankyou very much! I will try it tonite.
>From: Marcia Selsor
>Reply-To: Clayart
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: joining porcelain
>Date: Sun, 5 Mar 2006 11:45:04 -0700
>
>Try mixing a paper patch for slip for joining. Use some of your
>porcelain, add toilet paper after soaking it overnight,
>add a drop of sodium silicate. Mix in a blender.
>Marcia Selsor
>On Mar 5, 2006, at 11:14 AM, tim knick wrote:
>
>>Why do I have so much trouble joining porcelain? Even if it is
>>wetter than
>>leather hard, it still cracks. I have tried wetting and scoring.
>>i have
>>tried smearing slip and scoring. I do not have this problem with a
>>grogged
>>stoneware. Any helpful hints out there?
>>Thanks,
>>Tim
>>
>>________
>
>______________________________________________________________________________
>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.
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Craig Martell on sun 5 mar 06
Hello Tim:
Porcelain is harder to join. Once you learn the technique for a porcelain
body the success rate is much better. I work with two porcelains and use
the same technique for both and have a pretty fair percentage of success.
Make the join as soon as you can handle the pot. I use soft clay to pull
handles and I usually pull the handle off the piece. I will pull a short
stub, cut if off and flare the cut end with a wet finger to have more clay
around the edge for joining. I always score the pot but not the handle
stub. I don't use slip, just water. Slip has a lot of fines and is very
wet so the shrinkage of the slip is higher than the pot and handle. This
can cause cracking. When joining, really push the handle on and work the
edges in very well. You will need to support the inside of the pot while
doing this if it's possible.
As far as not scoring goes, if you can pull it off, great! My feeling is
that scoring allows greater penetration of the handle into the pot and,
after all, the idea is to make one pieces out of two parts. That's why I
score the pot. I've tried both ways and I've had much greater success scoring.
After joining, cover the pots for a day or two to equalize the water
content of both parts. If there are hairline cracks that develop, use a
stiff, slightly wetted brush to "erase" them. You can do this a few times
until the pot is dry.
hope this helps, Craig Martell Hopewell, Oregon
tim knick on sun 5 mar 06
Paper clay. I will try that, one other response gave me a way to do just a
patch of paper clay for the joint. Thankyou,
Tim
>From: Peter Cunicelli
>Reply-To: Clayart
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: joining porcelain
>Date: Sun, 5 Mar 2006 15:02:28 -0500
>
>Hey Tim,
>
>I've had these problems in the past as well.
>
>Some things I've learned are:
>
>Use reinforcement coils at the joins. This really helped a lot. I also
>paddle all my joins with a piece of wood. It's really important that you
>press the coil into the join so that there's no air bubbles. That can be
>ugly.
>
>Bevel the two pieces that are to be joined in order to make the join
>stronger.
>
>Score deeply and close together.
>
>Use a really thick slurry.
>
>Porcelain has to be dried very, very slowly. When I finish a piece, I
>cover it lightly with plastic and let it sit for a day to as long as a
>week. Most of my work is very dry when I'm finished with it anyway.
>
>I've also found that burnishing helps a lot.
>
>Recently, I've been taking a class in paper clay. All of the above,
>apparently, are no longer applicable. I don't score the joins. I use
>water, not slurry. I do paddle and bevel, however. I did make a few
>pieces with paper clay and they made it all the way through the glaze
>firing without any of the big issues you seem to be having. I'm pretty
>sure I'm a paper clay convert now.
>
>Hope this helps.
>
>Peter
>(www.petercunicelli.com)
>
>______________________________________________________________________________
>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.
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tim knick on sun 5 mar 06
Thankyou, I ordered Darvan 7 earlier today which is the same thing I
think.
Hopefully it solves my problem.
Thanks for responding!
Tim Knick
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tim knick on sun 5 mar 06
Thankyou for the response. I suspect the culpret may be that I have not
been covering my stuff to dry slow. I live in dry winter wisconsin. Also I
got a recipe for vinegar, sugar and slip. I ordered deflocculant today too.
One of these things should work for me.
Thankyou,
Tim Knick
>From: Craig Martell
>Reply-To: Clayart
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: joining porcelain
>Date: Sun, 5 Mar 2006 16:26:22 -0800
>
>Hello Tim:
>
>Porcelain is harder to join. Once you learn the technique for a porcelain
>body the success rate is much better. I work with two porcelains and use
>the same technique for both and have a pretty fair percentage of success.
>
>Make the join as soon as you can handle the pot. I use soft clay to pull
>handles and I usually pull the handle off the piece. I will pull a short
>stub, cut if off and flare the cut end with a wet finger to have more clay
>around the edge for joining. I always score the pot but not the handle
>stub. I don't use slip, just water. Slip has a lot of fines and is very
>wet so the shrinkage of the slip is higher than the pot and handle. This
>can cause cracking. When joining, really push the handle on and work the
>edges in very well. You will need to support the inside of the pot while
>doing this if it's possible.
>
>As far as not scoring goes, if you can pull it off, great! My feeling is
>that scoring allows greater penetration of the handle into the pot and,
>after all, the idea is to make one pieces out of two parts. That's why I
>score the pot. I've tried both ways and I've had much greater success
>scoring.
>
>After joining, cover the pots for a day or two to equalize the water
>content of both parts. If there are hairline cracks that develop, use a
>stiff, slightly wetted brush to "erase" them. You can do this a few times
>until the pot is dry.
>
>hope this helps, Craig Martell Hopewell, Oregon
>
>______________________________________________________________________________
>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.
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William & Susan Schran User on mon 6 mar 06
On 3/5/06 3:50 PM, "tim knick" wrote:
> Paper clay. I will try that, one other response gave me a way to do just a
> patch of paper clay for the joint.
Two ways I join handles to cups, or whatever.
#1 - Paperclay. I use institutional toilet paper. They use those big honkin'
rolls of toilet paper at school. Cleaning crew saves the end-of-roll-remains
for me. Paper torn up, beaten with hot water, water squeezed out, mixed to
approximate proportion 1/3 paper pulp to 2/3 clay slip, blended well. When
finished, spread remaining slip out, allow to dry. Break off piece of dry
paperclay and mix to slip when needed.
Repairs/fills cracks in greenware, have repaired bisque ware cracks, works
well for porcelain attachments.
#2 - Wet & Slip. I use this for stoneware.
Score/scratch area of attachment.
Wet slightly with water, bringing area to almost moist clay state.
Apply dab of slip, attach handle.
Dry slowly under plastic.
Then, of course, my beginning students follow this method,
But forget to cover their work with plastic,
And their handles never crack!
Damn, damn, I guess if you don't know you're doing something wrong then it
will work - that's how we discover new things!
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Katharina Schulz on mon 6 mar 06
Hi Tim,
it is the usual problem with porcelain... and it is rather time
consuming.
But there are some tricks what one can do:
1. all items have to have the same level of dryness
2. after joining the items with slurry and scoring, your item has to dry
slowly (use a plastic sheet)
3. make sure all joint items are drying at the same rate... a handle
dries faster than the cup (cover it with some extra plastic or a wet
sheet).
4. during the drying process look for cracks, if you find any repair it
with a wet wooden modelling knife. Just smear the cracks close. If you
do it very diligently and with a sharp eye, you should see no cracks
after firing.
That should do it. It is awful lot of work, but that is porcelain ;)
Good luck
Katharina Schulz
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of tim knick
Sent: Monday, March 06, 2006 3:15 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: joining porcelain
Why do I have so much trouble joining porcelain? Even if it is wetter
than
leather hard, it still cracks. I have tried wetting and scoring. i
have
tried smearing slip and scoring. I do not have this problem with a
grogged
stoneware. Any helpful hints out there?
Thanks,
Tim
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________________________________________________________________________
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Ivor and Olive Lewis on tue 7 mar 06
It has been an education reading the replies to Tim Knick's question. So =
I will ask a supplementary question.
In a previous post I mentioned the market level for Mugs in the UK as =
being of the order of 200,000,000 per year, Given a population of about =
55,000.000 that means one in the kitchen, one by the computer, on in the =
shed..... Reckon The US of A needs a billion mugs a year !
For over fifty years handles have been attached mechanically. What do =
they use as an adhesive? Water !
Good and Bad technology can always be explained by Science. What is the =
Science behind Spooze? Behind Score and Slip? Behind paper reinforced =
slip? behind Vinegar? Come to think of it, why should anything be =
sticky? Why can other things be stuck too? From whence comes =
"Stickability"?
Best regards ,
Ivor Lewis.
Redhill,
South Australia.
Jim Murphy on tue 7 mar 06
Hi Ivor,
Scientifically-speaking, :o) , I believe 'stickability' is due mainly to
"hydrogen-binding", perhaps with a bit of surface tension as well.
I doubt Spooze, slip or even 'spittle' for that matter would "work" without
hydrogen-binding [from water as you point out].
Best wishes,
Jim Murphy
on 3/6/06 6:34 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
> For over fifty years handles have been attached mechanically. What do they use
> as an adhesive? Water !
>
> What is the
> Science behind Spooze? Behind Score and Slip? Behind paper reinforced slip?
> behind Vinegar? Come to think of it, why should anything be sticky? Why can
> other things be stuck too? From whence comes "Stickability"?
David Beumee on wed 8 mar 06
Dear Ivor,
I went to great pains for years to have just the right consistency clay body slip for attaching handles onto porcelain mugs, and then Pete Pinnell shattered all that at a workshop when he said, "water works just fine!" Sure enough..........
Just completed my first glaze firing in my brand new relined kiln; a wonderful success. The fiber had been there since the early seventies and I replaced it with lovely insulating fire brick, K-23's and K-26, and a beautiful arch. What a treat!
David Beumee
Lafayette, CO
-------------- Original message ----------------------
From: Ivor and Olive Lewis
> It has been an education reading the replies to Tim Knick's question. So I will
> ask a supplementary question.
>
> In a previous post I mentioned the market level for Mugs in the UK as being of
> the order of 200,000,000 per year, Given a population of about 55,000.000 that
> means one in the kitchen, one by the computer, on in the shed..... Reckon The US
> of A needs a billion mugs a year !
>
> For over fifty years handles have been attached mechanically. What do they use
> as an adhesive? Water !
>
> Good and Bad technology can always be explained by Science. What is the Science
> behind Spooze? Behind Score and Slip? Behind paper reinforced slip? behind
> Vinegar? Come to think of it, why should anything be sticky? Why can other
> things be stuck too? From whence comes "Stickability"?
>
> 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.
Ivor and Olive Lewis on thu 9 mar 06
Dear Jim Murphy=20
Thanks for your response.
There is agreement in the literature that the nature of plastic clay is =
due to Hydrogen bonding of water molecules to water molecules to plastic =
clay.
But then the picture begins to get murky. Have you noticed how, when =
plastic clay is stressed or bent coarse fragments of grog and sand will =
separate from the smoother stuff as fissures start to form. Have you =
noticed how fines seem to wash away from the surface when you are =
throwing leaving a coarse fraction that feels abrasive when passing =
under your fingers. These bits seem to lack "Stickability" even though =
they are wet or damp.
Best regards,
Ivor
Jim Murphy on thu 9 mar 06
Hi Ivor,
Just a few quick thoughts:
If we're going to 'believe' the literature is anything close to "reality",
then those relatively "large" grog or sand particles [near the surface]
would have many inherent "weaknesses" [compared to fine clay particles]
including:
1. small surface area whereas ball-clays have large surface areas for extra
"cling-capability" [layman's term ;o)]
2. lower charge-strength
3. 'hill & valley' topography [where many ice-like 'rivers' run through,
each a potential fault-line for fissures and allowing finer clay particles
to be washed away by centripetal forces (during throwing).
Best wishes,
Jim
on 3/8/06 6:41 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
> But then the picture begins to get murky. Have you noticed how, when plastic
> clay is stressed or bent coarse fragments of grog and sand will separate from
> the smoother stuff as fissures start to form. Have you noticed how fines seem
> to wash away from the surface when you are throwing leaving a coarse fraction
> that feels abrasive when passing under your fingers. These bits seem to lack
> "Stickability" even though they are wet or damp.
Anne Webb on fri 10 mar 06
Hey Tim..
I just use straight vinegar in putting on handles and i have very little
cracking at all. I score both handle and mug, brush on vinegar, attach the
handle and compress the joint well. Then I dry the pot *slowly*. After
attaching the handle, I put the pot in an old refrigerator with a cup of
water in the bottom of it. I leave the pot in there for a few days to "rest"
before I remove it and dry it slowly under plastic.
Everyone has their own special thing about attaching. Some people score,
some do not believing it weakens the joint. I've tried spooze, slip, &
"magic water" (a mix with sodium silicate in it), but I've gotten best
results when I went back to using plain ole vinegar. ..simplicity huh?
It sounds, however, more like your problem is in the drying process. Just a
suggestion, but you might like to think about setting yourself up some sort
of a damp closet, whether it be an old refrigerator or something as simple
as a ware rack wrapped in plastic. Wouldnt cost you much and it may make the
difference for you.
Would be interested to hear how you make out and what works best for you :)
Keep us posted.
Cheers! Anne
>From: tim knick Why do I have so much trouble joining porcelain? Even if
>it is wetter than
>leather hard, it still cracks.
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Ivor and Olive Lewis on fri 10 mar 06
Dear Jim Murphy,
I like your comments..."
1. small surface area whereas ball-clays have large surface areas for =
extra
"cling-capability" [layman's term ;o)]
2. lower charge-strength
3. 'hill & valley' topography [where many ice-like 'rivers' run through,
each a potential fault-line for fissures and allowing finer clay =
particles
to be washed away by centripetal forces (during throwing).
Must say, you have keen eyesight to see all this. Best I can manage is =
to see and feel the grog and the grit. Never thought about the idea of =
the water we use being like a glacier. I suppose your "Weaknesses" in =
the grit and such stuff would be cleavage planes. Never read about this =
in the popular literature.
Enjoy the weekend. Quiet today isn't it !!!!!
All the best,
Ivor.
You have a great imagination.
=20
Ivor and Olive Lewis on sun 12 mar 06
I do not dispute the fact that Vinegar can cause damp clay to adhere to =
damp clay. I have found by testing that Vinegar can also cause unfired, =
bone dry clay to adhere to unfired, bone dry clay (without any need for =
scoring) with a very strong bond.
Given that culinary vinegar is approximately 95% Water and only 5% =
Acetic acid, what difference does such a small percentage of acetic acid =
make ??
I can find no scientific explanation in the literature. Frank Hamer =
writes that Acetic acid Flocculates a clay slip (See page 1 under Acid) =
and that the effect is not permanent (Page 129, under Flocculation). But =
applied to both plastic clay and dry clay this is nonsense because one =
is, supposedly, already in the Flocculated condition and the other is =
thought to be an assembly of mineral particles bound by electronic =
forces or crystallised solutes, so floc structures are irrelevant.
Hence, I wonder if someone can tell us with some degree of certainty =
what the Science is for this technique.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Jim Murphy on sun 12 mar 06
Hi Ivor,
Bone dry clay in a low-pH environment ... hmmmm ???
The "science" suggests a flocculated [edge-to-surface] bone dry clay
structure.
Two other distinguishing characteristics of bone dry clay:
1. Since most of the free-water is gone, the ice-like "structured-water"
[Brownell, et al] consists mainly of the firmly-bonded surface "adsorbed"
water-layer [with less of an extended double-diffuse free-water layer as in
'wet' clay].
2. More pronounced 'pores', or capillaries between "dry" particles.
Research in "aqueous" clay solution has shown clay "adsorbed" water-film is
"thicker" at clay particle surfaces than clay particle edges. [I'm not sure
though if this still holds true for bone dry clay :o( ]
Also of note, clay particle "edges" are said to be positively-charged in
acid solution.
Although culinary vinegar may only be 5% acetic acid, I'd say what's more
important to consider is the relative change in "thickness" of
structured-water layer DUE TO the additional "acidic" pore-water solution.
By adding vinegar, the water-film thicknesses [adsorbed surface layer AND
extended double-diffuse free-water layer] are changing, and accordingly, so
is the bond-strength.
Perhaps making "strong" edge-to-surface bonds.
Best wishes,
Jim
on 3/11/06 6:25 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
> I do not dispute the fact that Vinegar can cause damp clay to adhere to damp
> clay. I have found by testing that Vinegar can also cause unfired, bone dry
> clay to adhere to unfired, bone dry clay (without any need for scoring) with a
> very strong bond.
Sam Miller on sun 12 mar 06
Ivor asks...
" ...Vinegar can also cause unfired, bone dry clay to adhere to
unfired, bone dry clay (without any need for scoring) with a very
strong bond. Given that culinary vinegar is approximately 95% Water
and only 5% Acetic acid, what difference does such a small percentage
of acetic acid make ?? ......Hence, I wonder if someone can
tell us with some degree of certainty what the Science is for this
technique?"
Ivor,
I have not done experimentation to prove this hypothesis nor can I
cite a specific reference for my statements, but I will endeavor to
speculate what may be happening as a means of sparking the discussion.
I would speculate that the presence of the acetic acid (even at low
concentrations) promotes increased hydrogen bonding due to the
dissociation of the hydrogen ion of acetic acid in an aqueous
solution (acetic acid anion is floating about and encouraging other
molecules to share their hydrogen ions, which contributes to more H-
bonding). I don't know why this effect would continue for bone dry
ware unless the structure of the clay at the site of attachment is
modified slightly due to the increased H-bonding to cause a more
permanent association between the two surfaces.
You have studied clay chemistry more than most of us, does this
notion of the bone dry clay molecule "re-association" with the
presence of increased H-bonding make sense?
Thanks!
Sam Miller
"Texas Dabbler"
come visit me at my Frappr site...
www.frappr.com/sammiller
Ruth Ballou on mon 13 mar 06
Hello All,
My mother referred this thread to me. I have trained as a chemist,
and spent some time studying solution-surface interactions, though
this is by no means my speciality. I've tried to keep the explanation
as non-technical as possible, and include some links that I think
clearly and concisely explain the issues involved.
Sam,
You are of course correct about the dissociation of acetic acid in
solution, and this property is partially responsible for the
phenomenon you are observing. But I would speculate that the physical
consequences of increased H-bonding in this case are small, keeping
in mind that H-bonds are the weakest types of chemical bonds, and
even at optimal conditions would not significantly increase the
strength of a mechanical bond between two pieces of clay. Instead, I
suspect that what you all are observing is a consequence of the
hydrophobic nature of vinegar, resulting in what is called the
"wettability" of the clay in relation to vinegar. You can check out
this article in the wikipedia for more information about wetting
(http://en.wikipedia.org/wiki/Wetting). In the figure, A can be
considered the behavior of water (with a contact angle of 90 degrees
or greater) and C more closely describes the contact angle of
vinegar. You all can observe this behavior yourselves just by placing
a small drop of water and a small drop of vinegar on any surface and
watching. The vinegar will spread out, while the water will tend to
stick to itself. So, when vinegar is used to join two pieces of clay,
it adsorbs into the clay faster and helps make the mechanical bond
"better." This article (http://en.wikipedia.org/wiki/Adhesion), also
in the wikipedia, explains a bit about the difference between a
mechanical bond (between two pieces of clay) and a chemical bond
(between molecules, for example what happens in a glaze when it its
heated). There is also a link on this page that gets into a more
detailed discussion of what makes a strong mechanical bond.
Hope this helps.
Liz Ballou
On Mar 12, 2006, at 8:26 PM, Sam Miller wrote:
> Ivor asks...
>
> " ...Vinegar can also cause unfired, bone dry clay to adhere to
> unfired, bone dry clay (without any need for scoring) with a very
> strong bond. Given that culinary vinegar is approximately 95% Water
> and only 5% Acetic acid, what difference does such a small percentage
> of acetic acid make ?? ......Hence, I wonder if someone can
> tell us with some degree of certainty what the Science is for this
> technique?"
>
> Ivor,
>
> I have not done experimentation to prove this hypothesis nor can I
> cite a specific reference for my statements, but I will endeavor to
> speculate what may be happening as a means of sparking the discussion.
>
> I would speculate that the presence of the acetic acid (even at low
> concentrations) promotes increased hydrogen bonding due to the
> dissociation of the hydrogen ion of acetic acid in an aqueous
> solution (acetic acid anion is floating about and encouraging other
> molecules to share their hydrogen ions, which contributes to more H-
> bonding). I don't know why this effect would continue for bone dry
> ware unless the structure of the clay at the site of attachment is
> modified slightly due to the increased H-bonding to cause a more
> permanent association between the two surfaces.
>
> You have studied clay chemistry more than most of us, does this
> notion of the bone dry clay molecule "re-association" with the
> presence of increased H-bonding make sense?
>
> Thanks!
>
> Sam Miller
>
> "Texas Dabbler"
>
> come visit me at my Frappr site...
>
> www.frappr.com/sammiller
>
> ______________________________________________________________________
> ________
> 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.
>
Sam Miller on mon 13 mar 06
Hey Liz,
Thanks for the refresher on surface chemistry! The question that
Ivor raised about joining bone dry clay with vinegar is the most
interesting to me. What do you suppose might be happening at the
interface of two pieces of bone dry clay in the presence of a dilute
acid solution?
Thanks again for your contribution!
Sam
"Texas Dabbler"
On Mar 13, 2006, at 12:20 PM, Ruth Ballou wrote:
>
> I suspect that what you all are observing is a consequence of the
> hydrophobic nature of vinegar, resulting in what is called the
> "wettability" of the clay in relation to vinegar.
Ivor and Olive Lewis on tue 14 mar 06
Dear Sam Miller,
Interesting proposition you put forward, but you have to complete the =
picture. Lone protons do not wander about without doing something. In an =
aqueous environment they team up with other water molecules to make =
Hydronium Ions (H3O+) or with free hydroxyl ions (OH-) to make water. I =
could not say how this would relate to vinegar and dry clay. What I do =
know is that when bone dry clay is put into water it rapidly breaks =
apart into fragments that readily subdivide into fine detritus, in other =
words, Mud !
The thing which interests me is that two of the leading commentators =
have opposing views on what Vinegar will do. Frank Hamers says it will =
Flocculate a clay/water system while Robert Fournier says it will =
deflocculate a clay/water system.
Rhodes suggests that Magnesium sulphate and Aluminium sulphate =
flocculate glaze mixtures but says nothing about clay and nothing about =
vinegar.
Hutchinson Cuff suggests using Calcium chloride and other metallic salts =
and also Hydrochloric acid or vinegar as flocculants. But nowhere do any =
of these authors explain the science behind their recommendations.
Speculation is one thing and it may assist in continuing the discussion. =
But speculation never solved problems. It always leads me back to =
suggesting that some pretty deep study be done. I have also said, the =
answer will come from applying fundamental concepts of Chemical Science. =
An answer can be constructed from information in Linus Pauling's text =
book
Taking you Hydrogen bond as an example. This process is responsible for =
Acetic acid molecules joining together to form larger molecules (Dimeric =
molecules or "Dimers") via links across their Carboxyl groups. This =
effectively sequesters hydrogen atoms and prevents them from becoming =
free roaming spirits. It prevents Acetic acid dissociating into ions. So =
Vinegar has physical properties analogous to those of Water, which also =
relies on Hydrogen bonding for its properties, except that the phase =
changes of Acetic acid have higher temperatures.
Thanks Sam, for keeping my mind agile.
Best regards,
Ivor
Katharina Schulz on tue 14 mar 06
Thanks to Liz and Ivor for all your insights.
I just have a question to Ivor. You wrote that vinegar is able to join
bone dry clay with bone dry clay with a very strong bond.
" I have found by testing that Vinegar can also cause unfired, bone dry
clay to adhere to unfired, bone dry clay (without any need for scoring)
with a very strong bond"
What do you mean with "with a very strong bond"? Is it slip with
vinegar?
And does it work with porcelain?
Thanks
Katharina Schulz
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Sam Miller
Sent: Tuesday, March 14, 2006 9:21 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: joining porcelain
Hey Liz,
Thanks for the refresher on surface chemistry! The question that
Ivor raised about joining bone dry clay with vinegar is the most
interesting to me. What do you suppose might be happening at the
interface of two pieces of bone dry clay in the presence of a dilute
acid solution?
Thanks again for your contribution!
Sam
"Texas Dabbler"
On Mar 13, 2006, at 12:20 PM, Ruth Ballou wrote:
>
> I suspect that what you all are observing is a consequence of the
> hydrophobic nature of vinegar, resulting in what is called the
> "wettability" of the clay in relation to vinegar.
________________________________________________________________________
______
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.
Eleanora Eden on tue 14 mar 06
Hi Peter and all,
Peter said:
"Use reinforcement coils at the joins. This really helped a lot. I also
paddle all my joins with a piece of wood. It's really important that you
press the coil into the join so that there's no air bubbles. That can be
ugly."
Rather than paddling, I use a wooden smoothing tool to work at that joint
and compress the clay into that joint as best I can. When I pull my
handles I leave the mess there initially so I can have this extra clay
to compress into the joint. This has mostly eliminated the cracking around
handles that used to plague me.
If something does start cracking I just work at it more, compressing that
cracked place smooth.
Hope this helps.
Eleanora
www.eleanoraeden.com
skiasonaranthropos@FSMAIL.NET on tue 14 mar 06
Hello Ivor,
Could you expand upon your statement =93 ... deep study be done=94 as my
interpretation of your message is that youre suggesting that this be on the
nature of flocculating clay particles, which is of course well established.
And Im really puzzled about your reference to claims that acid
deflocculates a clay/water system as it clearly is the opposite
Regards,
Antony
Ivor and Olive Lewis on wed 15 mar 06
Dear Ruth Ballou,=20
Thank you for your contribution to this thread.
Accepting what you say and looking at the two sites you suggested, the =
information does not tell us why it is possible for Vinegar to have two =
contradictory functions. How would you explain Dilute Acetic Acid acting =
as a flocculant, as told to us by Frank Hamer and as a deflocculant, as =
written by Robert Fournier ? Wikipedia throws no light on this question =
though I would accept your suggestion that the dissociation of Acetic =
acid in water is central to solving the puzzle.
I know that clay surfaces that have been wetted with vinegar and pressed =
together will form a strong union. I have tested this with several =
pieces of clay. It works and if you get a good "Take" you cannot pull =
the parts away from each other with your fingers. But is it doing what =
Frank Hamer says ? Or is it behaving as Robert Fournier tells us. Which =
is it ? Why does it happen ? Are we Flocculating or are we =
Deflocculating ? Or does neither occur ?
I must test your observations about Vinegar readily wetting clay and =
Clay being hydrophobic towards Water. My experience is that when water =
is poured over crushed clay it decomposes quickly into Mud. I use this =
fact to etch clay so that I can reveal flow structures.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Dave Finkelnburg on wed 15 mar 06
Ivor,
Regarding the effect of vinegar, you may want to
consult Australian author R.J. Hunter, "Introduction
to Modern Colloid Science."
As to Hamer and Fournier, obviously one of them is
wrong. That's because at the time of their
writing...and even today...there exists an imperfect
understanding of the surface chemistry involved in
clay systems.
I confess I have questions about this subject,
too. For example, as I understand it clay (kaolinite)
systems naturally flocculate at near-neutral pH.
However, vinegar has a pH of ~2.5-3.2. Is that low
enough to flocculate silica and deflocculate alumina?
You keep asking questions. I'm looking for
answers! :-) I hope the changing of seasons is
bringing you relief from the summer's heat.
Dave Finkelnburg
> on 3/14/06 11:01 PM, Ivor and Olive Lewis at
> wrote:
> and why do Hamer and Fournier give opposite
> opinions.
__________________________________________________
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Charles Manuel on wed 15 mar 06
Dear Ivor,
=20
I hope you all don't mind if I share my observations working with =
vinegar. In a suggested answer to the apparent contradiction of the two =
observations of vinegar acting like a flocculant and deflocculant, I =
believe an answer would lay with the knowledge that vinegar, being an =
acid, has a negative charge. Most plate like clay particles have a =
positive charge. Vinegar reacting with such surfaces would act with an =
attractive force between the two particles hence the flocculating =
effect. I used it to flocculate my clay in grad school for my local clay =
processing. Smelled up the studio much to the chagrin of the other grad =
students :-) A good description of the clay particle structure etc. is =
in Michael Cardews book Pioneer Pottery. I use it to explain it to my =
students. We use vinegar exclusively when combining clay now and have =
observed the possibility of joining bone dry pieces together without =
separation in firing. I experimented spraying a porcelain vinegar slip =
on bone dry fluted stoneware teapots with success. I can make pictures =
available to those interested.
With this observation of the flocculating/attracting properties of =
vinegar with most clay, wouldn't it be possible if there were sufficient =
negative charges in certain clay bodies due to chemical diversity for =
the vinegar to act as a dispersant rather than an attractant? Just a =
thought. If anyone is interested in how we have used the vinegar for =
other things, I will be happy to share.
=20
Chuck Manuel
Lamoni, IA
cemanuel@graceland.edu
________________________________
From: Clayart on behalf of Ivor and Olive Lewis
Sent: Tue 3/14/2006 10:59 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: joining porcelain
Dear Ruth Ballou,
Thank you for your contribution to this thread.
Accepting what you say and looking at the two sites you suggested, the =
information does not tell us why it is possible for Vinegar to have two =
contradictory functions. How would you explain Dilute Acetic Acid acting =
as a flocculant, as told to us by Frank Hamer and as a deflocculant, as =
written by Robert Fournier ? Wikipedia throws no light on this question =
though I would accept your suggestion that the dissociation of Acetic =
acid in water is central to solving the puzzle.
I know that clay surfaces that have been wetted with vinegar and pressed =
together will form a strong union. I have tested this with several =
pieces of clay. It works and if you get a good "Take" you cannot pull =
the parts away from each other with your fingers. But is it doing what =
Frank Hamer says ? Or is it behaving as Robert Fournier tells us. Which =
is it ? Why does it happen ? Are we Flocculating or are we =
Deflocculating ? Or does neither occur ?
I must test your observations about Vinegar readily wetting clay and =
Clay being hydrophobic towards Water. My experience is that when water =
is poured over crushed clay it decomposes quickly into Mud. I use this =
fact to etch clay so that I can reveal flow structures.
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.
Ivor and Olive Lewis on thu 16 mar 06
Dear Katharina Schulz,
Using the process described by Robert Fournier,"Illustrated Dictionary =
if Practical Pottery" under 'Vinegar', page 44 and I quote "Contains =
3-6% acetic acid. It has a deflocculating effect on clay and can be used =
to repair dry pots or modelling (so long as the damage is not he result =
of strains. Work the vinegar with a brush on both surfaces and press =
them together. .....it must not be used on handles"
I have so far tried it on flat test pieces (one inch cubes of clay) made =
from stoneware clay. Direct pulling with both hands did to cause =
fracture. If the two parts were twisted in opposite direction it would =
break but a fair degree of force was needed. I know this is empirical =
but I had success with all of the bonds I made with vinegar direct from =
the bottle.
Would it be successful on Porcelain ? I would anticipate that it would. =
I will be working with some porcelain clay next week so I will make some =
test pieces and see what happens.
What concerns me is that two respected authorities give such contrasting =
opinions.
Can both be right ? If they are, how can the difference be explained? It =
is common knowledge that acids improve the workability of plastic clay. =
Claim is made that it Flocculates the clay. There is some confusing =
information circulating and it needs to be sorted out.
Thanks for your interest.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on thu 16 mar 06
Dear Antony,
Thanks for joining up on this thread.
You say... "I'm really puzzled about your reference to claims that acid =
deflocculates a clay/water system as it clearly is the opposite"....
Precisely, Frank Hamer makes that quite clear. Acids and acidic salts =
flocculate clay. But Robert Fournier gives the contrary information I =
have quoted in my post to Katharina Schulz. Logically, from Hamers =
information Vinegar, being and acid, must flocculate clay. Fournier Says =
that it deflocculates. This is unequivocal. It is published, in the =
public arena. Is one of them wrong and the other correct. Or is it =
possible that they are both telling the truth and no one has reconciled =
the argument. Or has Acetic Acid qualities that have been ignored by =
those who's research and writing we respect and employ.
Perhaps there is no simple answer that is easily understood.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Do you have an answer?
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on fri 17 mar 06
Dear Chuck Manuel,=20
Thank you for your contribution to this thread. There is so much we do =
not know so everyone who can make a contribution is welcome to have =
their say.
Yes, "Pioneer Pottery" is a very good reference for technical answers. =
More recent research has shown that the edges of clay crystals have both =
negative and positive charges whereas the tetrahedral Silica cleavage =
planes have negative charges from exposed Oxygen atoms and the =
octahedral Gibbsite layer which expose cleavage plane Hydrogen atoms =
have a positive charge. If you take Cardew's map of atom placement in =
the Kaolinite and allocate the distribution of electrons according to =
VSEPR theory this becomes obvious.
Your final statement is interesting but I am wondering if this is a =
contradiction of what you say in you first statement. No doubt this is =
what Robert Fournier is implying when he says Vinegar acts as a =
deflocculant. Essentially acids are neutral with respect of free =
charges. It is only when they are mixed with water that they ionise. =
Then, the pictures that emerge depend on which theory of Acids and =
Alkalies you subscribe to.=20
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Dave Finkelnburg on fri 17 mar 06
Ivor,
I'm sure you're aware of this, but for those who
may not be, the double layer or water hull theory
(admittedly only a theory) explains the flocculating
effect of adding cations to a clay slurry. Once the
cation concentration becomes high enough (reaches the
Critical Coagulation Concentration or CCC) the
particles can get close enough that the system
flocculates.
Monovalent cations (Na+, K+) are not very
efficient but divalent cations (Ca++, Mg++) are
roughly 8-times as effective at flocculating a system
of the same density. Trivalent cations (Al+++) are
another 8-times or so as effective a flocculant.
This is why Epsom salts (MgSO4) and calcium
chloride (CaCl2) flocculate a clay slurry.
Good potting,
Dave Finkelnburg
--- Ivor and Olive Lewis <> wrote:
> Rhodes suggests that Magnesium sulphate and
> Aluminium sulphate flocculate glaze mixtures but
> says nothing about clay and nothing about vinegar.
>
> Hutchinson Cuff suggests using Calcium chloride and
> other metallic salts and also Hydrochloric acid or
> vinegar as flocculants. But nowhere do any of these
> authors explain the science behind their
> recommendations.
__________________________________________________
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Charles Manuel on fri 17 mar 06
Thank you Ivor=20
You updated me most graciously. Reading as many of these posts as I can =
I am in awe of the knowledge base that is shared by so many that have =
been doing ceramics for years. I have 30 years to catch up with as after =
I graduated with my MFA in ceramics from UPS with Carlton Ball in '76. =
My path led to the health field as a chiropractor due to a back injury I =
was treated for and recovered from. I used my pottery to do shows and =
help pay my way through school but it was when I settled in the small =
college town of Lamoni, IA that my interest in ceramics lay dormant with =
periodic exposure teaching one semester at Graceland while they were =
looking to find a full time ceramics professor after my teacher Mel =
Clark left. Now after 30 years as I am winding down my private practice =
and entering my quote retirement phase, I was hired to teach ceramics at =
the University and am building up a program. I can't believe I have been =
able to be in such a position as it is a dream come true. I will be =
seeking most humbly, words of wisdom and expertise from the Clayart =
family as the program develops. First on the list is a 20cuft Olsen fast =
fire wood kiln to be built. I have to master the 2 24cuft Alpines we =
have as well. Thanks again for your explanation on joining porcelain.=20
Chuck Manuel
Lamoni, IA
________________________________
From: Clayart on behalf of Ivor and Olive Lewis
Sent: Fri 3/17/2006 12:02 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: joining porcelain
Dear Chuck Manuel,
Thank you for your contribution to this thread. There is so much we do =
not know so everyone who can make a contribution is welcome to have =
their say.
Yes, "Pioneer Pottery" is a very good reference for technical answers. =
More recent research has shown that the edges of clay crystals have both =
negative and positive charges whereas the tetrahedral Silica cleavage =
planes have negative charges from exposed Oxygen atoms and the =
octahedral Gibbsite layer which expose cleavage plane Hydrogen atoms =
have a positive charge. If you take Cardew's map of atom placement in =
the Kaolinite and allocate the distribution of electrons according to =
VSEPR theory this becomes obvious.
Your final statement is interesting but I am wondering if this is a =
contradiction of what you say in you first statement. No doubt this is =
what Robert Fournier is implying when he says Vinegar acts as a =
deflocculant. Essentially acids are neutral with respect of free =
charges. It is only when they are mixed with water that they ionise. =
Then, the pictures that emerge depend on which theory of Acids and =
Alkalies you subscribe to.
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.
Ruth Ballou on fri 17 mar 06
Hi All,
Ruth's daughter Liz here, again. Well, I've borrowed my mother's
textbooks, including Hamer, Fournier, and Lawrence, and studied what
they each say about the (de)flocculating nature of vinegar. For those
uninterested in the technical details, the last paragraph relates
more generally to the formation of joints.
Ivor
One point I should clarify from my previous post: when I talk about
vinegar as hydrophobic, I mean that it is hydrophobic towards itself,
with no reference to the clay. In other words, Vinegar is less
viscous, or more fluid, than water. This has to do with the structure
that H2O molecules adopt in solution. If you draw out H2O, (with
approximate bond angles of 180 deg on the long side), with weak H
bonds (drawn as dotted lines rather than solid lines) connecting the
O of one molecule to one H of another molecule, you will see that a
weak lattice quickly develops. Adding acetic acid to this effectively
disrupts this structure, because free H+ ions associate with the Os,
preventing H-bonds from forming. The liquid has less structure and
less surface tension, and is therefore more fluid than water.
So, what happens when this more fluid liquid comes in contact with a
solid? It penetrates pores more readily and separates large molecules
more quickly than water. I believe this process is called 'slaking.'
An experiment was performed in which 5g clay was observed in 15mL
each vinegar and water. Vinegar completely slaked the clay in less
than 4 min, while water did not completely slake the clay even after
20 min, at which point the experiment was stopped. So, vinegar slakes
more quickly than water.
Now for the tricky bit. Fournier defines deflocculation as "the
dispersion of particles ... to increase fluidity." Both Hamer and
Lawrence (and common sense) seem to agree. Fournier, Hamer, and
Lawrence also all agree that flocculants neutralize anions in clay,
resulting in decreased forces of repulsion that allow flocks to
form. Finally, all three state that a deflocculated material will
have a "stacked-card" structure, with all the particles lined up
resulting in decreased friction and easier movement (higher fluidity)
of the material in liquid. Great. Is this what is happening with
vinegar? Not really.
There are two degrees of interaction being observed in this problem.
The first is the interaction of the liquid with the clay slab. The
second is the interaction of the liquid with the colloid particles. I
think that what Fournier has observed as "increase fluidity" of clay
after the addition of vinegar is slaking (the first interaction)
rather than deflocculation (the second interaction).
Here's how I've explained all this: the effect of acetic acid is two-
fold. On one hand, H+ in the vinegar disrupts H-bonds. This decreases
H2O structure. The result is desolvated colloids (particles which are
no longer surrounded by structured water molecules). This makes
colloids more accessible to H+, which goes on to neutralize anions at
the edges of the colloids, thereby increasing the favorability of
particle interactions. The particles flock together. So. Even though
the vinegar is more fluid (less water structure) the clay particles
in the vinegar are less fluid (more particle structure).
->How does this all relate to joints? Well, adding vinegar to clay to
be joined slakes the clay at the joint more quickly, so the clay can
mingle more readily. Then the particles in the slake begin to flock
together, larger structure develops, and the result is a 'single'
solid piece of clay. Is this joint "better" because it is stronger?
Or just because it forms more quickly? Most likely it is because, as
Fourier states, a flocculated material adheres more easily and
undergoes less drying shrinkage, with less subsequent cracking and
flaking.
Regards,
Liz Ballou
On Mar 15, 2006, at 5:59 AM, Ivor and Olive Lewis wrote:
> Dear Ruth Ballou,
>
> Thank you for your contribution to this thread.
>
> Accepting what you say and looking at the two sites you suggested,
> the information does not tell us why it is possible for Vinegar to
> have two contradictory functions. How would you explain Dilute
> Acetic Acid acting as a flocculant, as told to us by Frank Hamer
> and as a deflocculant, as written by Robert Fournier ? Wikipedia
> throws no light on this question though I would accept your
> suggestion that the dissociation of Acetic acid in water is central
> to solving the puzzle.
>
> I know that clay surfaces that have been wetted with vinegar and
> pressed together will form a strong union. I have tested this with
> several pieces of clay. It works and if you get a good "Take" you
> cannot pull the parts away from each other with your fingers. But
> is it doing what Frank Hamer says ? Or is it behaving as Robert
> Fournier tells us. Which is it ? Why does it happen ? Are we
> Flocculating or are we Deflocculating ? Or does neither occur ?
>
> I must test your observations about Vinegar readily wetting clay
> and Clay being hydrophobic towards Water. My experience is that
> when water is poured over crushed clay it decomposes quickly into
> Mud. I use this fact to etch clay so that I can reveal flow
> structures.
>
> 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.
>
Ivor and Olive Lewis on mon 20 mar 06
Dear Liz, Daughter of Ruth Ballou
You say in your note ....."There are two degrees of interaction being =
observed in this problem.The first is the interaction of the liquid with =
the clay slab. The second is the interaction of the liquid with the =
colloid particles. I think that what Fournier has observed as "increase =
fluidity" of clay after the addition of vinegar is slaking (the first =
interaction) rather than deflocculation (the second interaction)."....
You may well be correct to suggest that there is a two stage reaction. I =
confirm the initial change that can be seen after raw vinegar is applied =
with a brush to the clay. But I would be unable to distinguish between a =
flock and a colloid particle with unaided sight.
So, why should Robert Fournier say that, and I quote from "Illustrated =
Dictionary of Practical Pottery, revised edition, 1977. Entry =
"Vinegar"...".....It has a deflocculating effect on the clay....." I =
have no quarrel with his entries for "Flocculation' or "Deflocculation" =
but this seems to be a definite statement inferring "...dispersion of =
particles...." given in entry "Deflocculation"=20
What I do know from observation or the interaction between clay and =
water and clay and vinegar using samples made by slaking 70 gram samples =
of ball clay and Kaolin in 30 grams samples of rain water is that when =
slaking is completed pastes made with dilute vinegar have a pH of 3.0, =
the one with ball clay and undiluted vinegar was pH 2.5 while the one =
with Ball Clay and rain water was close to 5.2 and Kaolin with rain =
water was close to pH 6.0.
All of which leaves my original question...." What is it about Acetic =
Acid/Water Solutions that confer deflocculating properties ?".... =
hanging.
Thank you for your thoughts on this matter. I am pleased Ruth brought =
you in on the thread.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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