Dave Finkelnburg on thu 7 feb 02
Kat,
I only know what I read in books and I still don't know anything....
:-) Only kidding!
I was reading, just this evening, in Vince Pitelka's book, "Clay, a
studio handbook," that, "....Pure kaolins are sometimes slightly alkaline
and therefore porcelain bodies should be flocculated with epsom salts...."
Vince later mentions the amount to use is 1/2-percent of the dry weight of
the clay batch.
Good potting!
Dave Finkelnburg
-----Original Message-----
From: Kat Fode
>For some reason I have a hard time believing that epson salts
>increase plasticity in a clay body. Has anybody else heard of
>that? I have been wrong before.
>However I have heard that adding epson salts to a body
>that contains sodium helps it from becoming
>thixotropic. As little as .3% is needed. Why would you need
>to add epson salts to a body for plasticity anyway?
vince pitelka on thu 7 feb 02
> For some reason I have a hard time believing that epson salts
> increase plasticity in a clay body. Has anybody else heard of
> that? I have been wrong before.
> However I have heard that adding epson salts to a body
> that contains sodium helps it from becoming
> thixotropic. As little as .3% is needed. Why would you need
> to add epson salts to a body for plasticity anyway?
Kat -
It seems odd to "have a hard time believing" if you do not understand the
chemistry of it. It only increases plasticity if the clay is slightly
alkaline, and that can happen easily. Alkalinity deflocculates the
claybody, making particles repel one another, which of course decreases
plasticity. Slight acidity flocculates, causing the particles to attract
one another, increasing plasticity. If the claybody is chemically neutral,
or slightly acidic, then adding Epsom salts will make no difference at all.
Acidity can most easily be introduced by adding 1/2 of 1% Epsom salts. It
is also introduced by aging clay, because the bacteria produce acidic
byproducts.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Kat Fode on thu 7 feb 02
For some reason I have a hard time believing that epson salts
increase plasticity in a clay body. Has anybody else heard of
that? I have been wrong before.
However I have heard that adding epson salts to a body
that contains sodium helps it from becoming
thixotropic. As little as .3% is needed. Why would you need
to add epson salts to a body for plasticity anyway?
Oh yeah and I don't have a Spell Chequer either. Loved the
spell checker poem.
Curious Kat in the Hat
Roger Korn on fri 8 feb 02
AHA! At last an explanation of the mechanism by which aging clay improves
plasticity. I have only observed that it works, but have never understood why. Also
accounts for the positive effects of adding urea used by Japanese and Korean
potteries (not getting into specifics).
Thanks, Vince,
Roger
vince pitelka wrote:
> ... It
> is also introduced by aging clay, because the bacteria produce acidic
> byproducts.
> Best wishes -
> - Vince
>
> Vince Pitelka
> Appalachian Center for Crafts
> Tennessee Technological University
> 1560 Craft Center Drive, Smithville TN 37166
> Home - vpitelka@dtccom.net
> 615/597-5376
> Work - wpitelka@tntech.edu
> 615/597-6801 ext. 111, fax 615/597-6803
> http://www.craftcenter.tntech.edu/
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
--
Roger Korn
McKay Creek Ceramics
In AZ: PO Box 463
4215 Culpepper Ranch Rd
Rimrock, AZ 86335
928-567-5699 <-
In OR: PO Box 436
31330 NW Pacific Ave.
North Plains, OR 97133
503-647-5464
iandol on sat 9 feb 02
Dear Kat Fode,
You say <increase plasticity in a clay body. Has anybody else heard of that? I =
have been wrong before.>>
My reading of the properties of Magnesium sulphate reveal that it is =
used to stop sedimentation of glaze slops which deflocculate and settle =
quickly due to the presence of soluble alkali ions. By neutralising or =
reversing the electronic forces the particles are supposed to come =
together in clumps. Some people call this "flocculation" and invent =
diagrams to show how it happens. However, there seems to be very little =
information around about the true nature of "flocks"
Hope that helps,
Ivor Lewis
mariko cruse on sat 9 feb 02
Dear Ivor,
From what you explained, am I right in interpreting that the sulphate ion of
the magnesium sulphate becomes part of sulfuric acid in solution, thereby
neutrlising the soluble alkali ions present? If so, would vinegar be just
as effective providin some hydrogen ions? Won't the magnesium cation
influence the claybody, if epsom salt is used? If I am way off, just
disregard my question, please. Mariko
----- Original Message -----
From: "iandol"
To:
Sent: Friday, February 08, 2002 11:52 PM
Subject: Epson Salts in Clay bodies
Dear Kat Fode,
You say <increase plasticity in a clay body. Has anybody else heard of that? I have
been wrong before.>>
My reading of the properties of Magnesium sulphate reveal that it is used to
stop sedimentation of glaze slops which deflocculate and settle quickly due
to the presence of soluble alkali ions. By neutralising or reversing the
electronic forces the particles are supposed to come together in clumps.
Some people call this "flocculation" and invent diagrams to show how it
happens. However, there seems to be very little information around about the
true nature of "flocks"
Hope that helps,
Ivor Lewis
____________________________________________________________________________
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iandol on sun 10 feb 02
Dear Mariko,
You ask <sulphate ion of the magnesium sulphate becomes part of sulfuric acid in =
solution, thereby neutralising the soluble alkali ions present?>>
My knowledge informs me that free sulphuric acid does not form when =
Magnesium sulphate is dissolved in water, nor, as far as I am aware does =
the pH value alter from neutral any more than Sodium chloride alters the =
pH of water or causes Hydrochloric acid to appear. These materials are =
salts. They dissolve in water and become "Ions" independent charged =
particles. It is these ions which alter overall electronic balance in =
wet clay. In some instances where there is a weak base and a strong =
acid, as in Ferric chloride, the solution becomes acidic and corrosive. =
But I understand this involves the dissociation of water and the =
creation of Hydronium ions.
I think the demonstration which was suggested should be a good concrete =
example of how these things behave in clay water systems. That is all =
that is needed.
Best regards,
Ivor.
Craig Clark on mon 11 feb 02
----- Original Message -----
From: "iandol"
To:
Sent: Sunday, February 10, 2002 12:17 AM
Subject: Re: Epson Salts in Clay bodies
Dear Mariko,
You ask <sulphate ion of the magnesium sulphate becomes part of sulfuric acid in
solution, thereby neutralising the soluble alkali ions present?>>
My knowledge informs me that free sulphuric acid does not form when
Magnesium sulphate is dissolved in water, nor, as far as I am aware does the
pH value alter from neutral any more than Sodium chloride alters the pH of
water or causes Hydrochloric acid to appear. These materials are salts. They
dissolve in water and become "Ions" independent charged particles. It is
these ions which alter overall electronic balance in wet clay. In some
instances where there is a weak base and a strong acid, as in Ferric
chloride, the solution becomes acidic and corrosive. But I understand this
involves the dissociation of water and the creation of Hydronium ions.
I think the demonstration which was suggested should be a good concrete
example of how these things behave in clay water systems. That is all that
is needed.
Best regards,
Ivor.
____________________________________________________________________________
__
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You may look at the archives for the list or change your subscription
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Ron Roy on wed 13 feb 02
Hi Mariko,
Got my kiln going today -
I have used vinegar and it does have the same effect as Epsom slats but -
The effect is not permanent
The vinegar produces such a bad smell that most people would not be able to
use it after a short period of time - like weeks.
An interesting experiment - make up some clay slip about 500 grams of dry
clay - say with EPK - make the consistency like Mayonnaise - a little
wetter - divide it in two. Add - drop by drop - vinegar to one half and
Epsom salts to the other half.
Drop by drop stirring as you do it -
It is an excellent way to thicken slips - just remember - when you
flocculate clay you raising the shrinkage and will have to add more water
to get the same consistency. This can be big trouble when applying slips -
better to deflocc to stop any cracking.
RR
>From what you explained, am I right in interpreting that the sulphate ion of
>the magnesium sulphate becomes part of sulfuric acid in solution, thereby
>neutrlising the soluble alkali ions present? If so, would vinegar be just
>as effective providin some hydrogen ions? Won't the magnesium cation
>influence the claybody, if epsom salt is used? If I am way off, just
>disregard my question, please. Mariko
>----- Original Message -----
>From: "iandol"
>To:
>Sent: Friday, February 08, 2002 11:52 PM
>Subject: Epson Salts in Clay bodies
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
mariko cruse on wed 13 feb 02
Hi Ron,
What do you mean by "Got my kiln going today"?
Thanks for your response. I read Hamer on the subject of flocc and
deflocc, but my brain is more flocculated than I thought. I still don't
understand how vinegar works as a flocculent. In regard to the experiment
you described: Is EPK alkaline or acidic? I got the impression from
Vince's post on the subject that the claybody must be alkaline in order to
be effective.
Since acidity or alkalinity affects plasticity of the clay bodies(am I
right?), how does one measure or determine the pH of the clay bodies?
Mariko
----- Original Message -----
From: "Ron Roy"
To:
Sent: Wednesday, February 13, 2002 12:54 AM
Subject: Re: Epson Salts in Clay bodies
> Hi Mariko,
>
> Got my kiln going today -
>
> I have used vinegar and it does have the same effect as Epsom slats but -
>
> The effect is not permanent
>
> The vinegar produces such a bad smell that most people would not be able
to
> use it after a short period of time - like weeks.
>
> An interesting experiment - make up some clay slip about 500 grams of dry
> clay - say with EPK - make the consistency like Mayonnaise - a little
> wetter - divide it in two. Add - drop by drop - vinegar to one half and
> Epsom salts to the other half.
>
> Drop by drop stirring as you do it -
>
> It is an excellent way to thicken slips - just remember - when you
> flocculate clay you raising the shrinkage and will have to add more water
> to get the same consistency. This can be big trouble when applying slips -
> better to deflocc to stop any cracking.
>
> RR
>
>
> >From what you explained, am I right in interpreting that the sulphate ion
of
> >the magnesium sulphate becomes part of sulfuric acid in solution, thereby
> >neutrlising the soluble alkali ions present? If so, would vinegar be
just
> >as effective providin some hydrogen ions? Won't the magnesium cation
> >influence the claybody, if epsom salt is used? If I am way off, just
> >disregard my question, please. Mariko
> >----- Original Message -----
> >From: "iandol"
> >To:
> >Sent: Friday, February 08, 2002 11:52 PM
> >Subject: Epson Salts in Clay bodies
>
> Ron Roy
> RR# 4
> 15084 Little Lake Rd..
> Brighton,
> Ontario, Canada
> KOK 1H0
> Residence 613-475-9544
> Studio 613-475-3715
> Fax 613-475-3513
>
>
____________________________________________________________________________
__
> 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.
vince pitelka on wed 13 feb 02
> you described: Is EPK alkaline or acidic? I got the impression from
> Vince's post on the subject that the claybody must be alkaline in order to
> be effective.
Mariko -
I don't know how you got that impression. An alkaline claybody is short and
unworkable. I said that flocculating the claybody with a mild acidic
substance or Epsom salts would not make any difference unless the claybody
started out being slightly alkaline. Then the Epsom salts would neutralize
the alkalinity and really make a difference. A claybody that starts out
flocculated is not going to change when you add Epsom salts.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
mariko cruse on thu 14 feb 02
Dear Vince,
I think you got me wrong. I thought that part of the reason why Ron
described "an interesting experiment" to me was so that I could see the
effect of a flocculent on clay. But, as you said,"......Epsom salts would
not make any difference unless the claybody started out being slightly
alkaline", I was wondering if the use of EPK prepares the condition for me
to see the neutralzing effect. May be, Ron was just telling me how to make
a good slip, based on the principle of flocculation.
Hamer says: Flocculants are acids or salts which act as acids.(p137, th ed.)
I am still not clear as to "act as acids". In a conventional sense, acid
implies the presence of hydrogen cations, which can be neutralized by the
presence of OH-, be it from a deflocculent or something similar. At any
rate, I don't think I misunderstood your statement. What do you think?
Best wishes,
Mariko
----- Original Message -----
From: "vince pitelka"
To:
Sent: Wednesday, February 13, 2002 9:09 PM
Subject: Re: Epson Salts in Clay bodies
> > you described: Is EPK alkaline or acidic? I got the impression from
> > Vince's post on the subject that the claybody must be alkaline in order
to
> > be effective.
>
> Mariko -
> I don't know how you got that impression. An alkaline claybody is short
and
> unworkable. I said that flocculating the claybody with a mild acidic
> substance or Epsom salts would not make any difference unless the claybody
> started out being slightly alkaline. Then the Epsom salts would
neutralize
> the alkalinity and really make a difference. A claybody that starts out
> flocculated is not going to change when you add Epsom salts.
> Best wishes -
> - Vince
>
> Vince Pitelka
> Appalachian Center for Crafts
> Tennessee Technological University
> 1560 Craft Center Drive, Smithville TN 37166
> Home - vpitelka@dtccom.net
> 615/597-5376
> Work - wpitelka@tntech.edu
> 615/597-6801 ext. 111, fax 615/597-6803
> http://www.craftcenter.tntech.edu/
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
vince pitelka on thu 14 feb 02
> Hamer says: Flocculants are acids or salts which act as acids.(p137, th
ed.)
> I am still not clear as to "act as acids". In a conventional sense, acid
> implies the presence of hydrogen cations, which can be neutralized by the
> presence of OH-, be it from a deflocculent or something similar. At any
> rate, I don't think I misunderstood your statement. What do you think?
Mariko -
You lost me on the chemistry. All I know is that Epsom salts or vinegar
will make the particles attract one another, making a much more plastic,
sticky clay. It seems that many kaolins have some residual alkalinity from
forming or processing, and therefore they can produce a severely short
(deflocculated) claybody if not flocculated in mixing.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
vince pitelka on fri 15 feb 02
> I'll not add to the discussion of epsom salts to a plastic claybody other
> than my preference is to select the correct clays from the get go, and use
> soem bentonite or macaloid. They really work wonders and I really don't
care
> about whether the body is alkaline or acidic or care to change that
balance.
> I'd rather use clays.
Jonathan -
This seems very curious and perhaps a little careless. I am not sure what
you mean by "the correct clays." Of course you want to select the right
clays for the properties of workability and finish you desire, but that will
not control whether there is any residual alkalinity in the clay. I am not
telling you anything you don't already know, and that is why your statement
seems especially curious. Adding bentonite or macaloid is not going to help
if the claybody is especially short due to residual alkalinity. The only
thing that will solve that is neutralizing the alkalinity with Epsom salts
or a mild acid.
Please do not imply that you don't care about whether the claybody is
alkaline or acidic, because you know that partical electrical charge has
everything to do with the performance of your plastic clay or your casting
slip. Alkaline = less plastic, acidic = plastic. When clay is aged the
bacteria make the clay more sticky and slippery partly due to the
accumulation of their slimy little dead bodies and partly due to their
acidic byproducts.
And many clayworkers comment on the magical combination of 2 or 3% bentonite
(or macaloid) AND 1/2 of 1% Epsom salts, because when those extra small
bentonite platelets become even stickier (due to the flocculation), then you
have some extremely plastic clay.
Of course, if the clays you use are not subject to residual alkalinity, then
you have no need for Epsom salts. Perhaps you have been lucky in that
regard.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Ron Roy on fri 15 feb 02
There are degrees of acidity and alkalinity - a slightly acidic body will
be made more "plastic" by adding more acid - or letting it age longer.
This has to do with the amount of water between each particle.
The stronger the attraction between each particle the more water that is
needed to move the particles - which is why focculated clay needs more
water.
As you rais e the alkalinity - deflocculation - the less water is needed
because the attraction between particles is less.
So if you follow the logic - a body that is already flocculated can be made
more flocculated by adding more acid or - whatever - you can have an over
flocculated body - or a slip - and the result is high shrinkage - and maybe
cracking.
The same is true of defloccing - if it is over done you have a very strange
acting clay - but if it is partially deflocced - well that explains the
differences in results we have posted.
How come some deflocced slips work just fine and some don't - what else
could be the answer?
RR
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Ceramic Design Group on fri 15 feb 02
> How come some deflocced slips work just fine and some don't - what else
> could be the answer?
>
Ron and others:
By "slips" I'll assume that discussion centers on casting slips.
Otherwise, I would use the word "engobe" or under-glaze to avoid any
confusion.
I deal with formulating casting slips both for our production as well as
consulting for others.
There are clays that are really poor choices for casting slips. There are
other clays that are my top ten or so for the best clays to use in casting
slips. Clay companies work very hard at blending their products from the
mine into the correct particle sizes for casting.
So one answer to Ron's question is that some clays deflocculate better
because they are specifically blended for that purpose. For instance, I
would not use OM-4 in a casting body. It can be deflocculated, but is a very
poor performer in a casting body. Plus it is full of all sorts of junk, but
that discussion is for another time. Casting depends on the presence of
organics to promote gelling which allows a clay/water mix to cast
successfully. Also, there are kaolins that are better performers than
others. Its all about particle size and gelling.
Another answer to Ron's question is that the choice of the CORRECT
deflocculant is critical.
I stay away from sodium silicate and soda ash. They are quite strong and
have a very short working range before they can thixoid a slip in a minute!
(how's that for making a very verb from an adjective/adverb) Plus soda ash
and sodium silicate really beat the heck out of plaster molds.
My preference is Darvan 811, one of the sodium polyacrylates from RT
Vanderbilt. It is a chained polymer that has a very broad working range and
requires very little to deflocculate a casting slip. It doesn't have a
negative effect on the casting molds either. We also use a bit in our glazes
to get the correct poise.
I'll not add to the discussion of epsom salts to a plastic claybody other
than my preference is to select the correct clays from the get go, and use
soem bentonite or macaloid. They really work wonders and I really don't care
about whether the body is alkaline or acidic or care to change that balance.
I'd rather use clays.
Jonathan
--
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
infor@ceramicdesigngroup.net www.ceramicdesigngroup.net
(use PO BOX for all USPS correspondence)
970 879-9139
Plant Location
1280 13th Street
Steamboat Springs CO 80487
(use PLANT LOCATION for all UPS, Common Carrier, and Courier deliveries)
Paul Herman on fri 15 feb 02
Hi Jonathan,
You say below that you would rather use bentonite or macaloid to
increase workability in throwing clays. My question is what is the
difference between the two? Macaloid (and Vee Gum-T) are listed in my
supplier's catalog as "bentonite" but why is it $5.00 a pound instead of
14 cents a pound like "bentonite"? It must be quite a refining process
to justify that.
Thanks,
Paul in Doyle
----------
>From: Ceramic Design Group
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: Epson Salts in Clay bodies
>Date: Fri, Feb 15, 2002, 12:09 PM
>
> I'll not add to the discussion of epsom salts to a plastic claybody other
> than my preference is to select the correct clays from the get go, and use
> soem bentonite or macaloid. They really work wonders and I really don't care
> about whether the body is alkaline or acidic or care to change that balance.
> I'd rather use clays.
>
> Jonathan
> --
Ceramic Design Group on sat 16 feb 02
on 2/15/02 9:27 PM, vince pitelka at vpitelka@DTCCOM.NET wrote:
>> I'll not add to the discussion of epsom salts to a plastic claybody other
>> than my preference is to select the correct clays from the get go, and use
>> soem bentonite or macaloid. They really work wonders and I really don't
> care
>> about whether the body is alkaline or acidic or care to change that
> balance.
>> I'd rather use clays.
>
> Jonathan -
> This seems very curious and perhaps a little careless.
I stated what works for me in over 30 years of blending and testing and
using clay bodies.
Curious yes, but not careless. I would posit from the get go the issues of
acidity and alkalinity in clay bodies further adds to the confusion of clay
body formulation. In fact, I would further posit that if there were some way
to gather and file in spread sheet format all the formulae that are out
there (no making any judgement whether they work or not) there would be
little reference to adding epsom salts or a mild acid. But this is not the
real issue anyways. IMHO, Most clay bodies that are out there are poorly
formulated in many ways, but that's my own judgement. I'll certainly not
malign any company on this formum. That's not the poin.
> I am not sure what
> you mean by "the correct clays." Of course you want to select the right
> clays for the properties of workability and finish you desire, but that will
> not control whether there is any residual alkalinity in the clay.
I have been mixing clays for well over 30 years and have never needed to add
these materials. Making a clay more workable may be a problem that can be
solved with such additions, but I would also posit that none of the clay
body manufacturers that I have worked with in 30 years uses epsom salts or a
mild/dilute acid. Maybe they are clueless? I don't know.
>I am not
> telling you anything you don't already know, and that is why your statement
> seems especially curious. Adding bentonite or macaloid is not going to help
> if the claybody is especially short due to residual alkalinity.
I would disagree, but its also not the point or the place to argue.
> The only
> thing that will solve that is neutralizing the alkalinity with Epsom salts
> or a mild acid.
So perhaps if you blend clay, a dash of vinegar (mildly acidic) will help.
We all know it does. But I would submit that if you take a non- plastic
kaolin such as grolleg and add the correct plasicizers, one could throw this
blend quite well. There are some admixtures/emusions/surfectants that are
being used in such bodies now, especially grolleg based bodies. There is a
very very white bentonite type material that is being used also. If
translucency in porcelains is desireable, then most potters stay away from
from ball clays because they don't know about the almost white burning ball
clays that are available.
>
> Please do not imply that you don't care about whether the claybody is
> alkaline or acidic, because you know that partical electrical charge has
> everything to do with the performance of your plastic clay or your casting
> slip.
I would submit and know very well that it has 99.99999% more to do with
casting bodies than plastic bodies. I can blend non-plastic fireclays and
kaolins and make some clay additions and render this body quite plasic
without the use of epsom salts or a mild acid.
>
> And many clayworkers comment on the magical combination of 2 or 3% bentonite
> (or macaloid) AND 1/2 of 1% Epsom salts, because when those extra small
> bentonite platelets become even stickier (due to the flocculation), then you
> have some extremely plastic clay.
Yes, sounds fine to me. You might want to reference a data sheet from the
producers of Macaloid....it talks about the product as bein ..."a
beneficiated hectorite of the monmorillonite (spelling?) classification.
The idea is that sure we could add all the junk types of bentonites, but
with the addition of the better materials, the product gets better.
>
> Of course, if the clays you use are not subject to residual alkalinity, then
> you have no need for Epsom salts. Perhaps you have been lucky in that
> regard.
I don't think luck has a whole lot to do with it. Study, research, and
testing are the key. We all know this. I know this and it has been part of
my daily life for many years.
I have recently formulated 3 cone 5-6 porcelain type whiteware bodies
suitable for pressing, jiggering, and throwing. Very low absorption,
shrinkage in acceptable parameters. They were wonderful to work without a
Macloid/Bentonite addition. Once I added 1/2% Macaloid or Hectalite, these
bodies became super plastic and incredibly wonderful to work with.
Its the same issues that are going to rear their ugly head when a "ClayArt
Clay Body" comes out. Not a time for this discussion now.
I think its a matter of finding materials or additions to clay bodies that
work for you and work with them. Notice my post didn't say that adding a
mild acid or epsom salts was wrong. My approach is just different, and I
would be very open to a a series of testing procedures what uses the
acid/alkaline theory and devising a precise test for plasticity that can be
used on bodies with these additions and with just clay additions. But this
may just be nit-picking anyway.
The important point is not a add to the confusion of an already overly
confused issue.
See you at NCECA.
Best
Jonathan
--
Jonathan Kaplan
CERAMIC DESIGN GROUP
PO Box 775112
Steamboat Springs, CO 80577
(970) 879-9139
info@ceramicdesigngroup.net
www.ceramicdesigngroup.net
-
>
Paul Herman on sat 16 feb 02
Hi Jonathan,
Would you share with us which of these ball clays are the almost white
ones?
Paul in Doyle
----------
>From: Ceramic Design Group
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: Epson Salts in Clay bodies
>Date: Sat, Feb 16, 2002, 7:06 AM
>
> then most potters stay away from
> from ball clays because they don't know about the almost white burning ball
> clays that are available.
Working Potter on sun 17 feb 02
Dear Jonathan,
You should write aa book on formulating claybodies[and anything else you
seem to know] as all your specialized experience would improve the
understanding when explained by someone with your extensive hands on
experience your posts demonstrate,
Thanks from those of us still learning after much ecperience as well.
Misty
Longtin, Jeff on mon 18 feb 02
A few thoughts:
Years ago I mixed Dorothy Hafner's ^6 Porcelain clay body. Among other
materials it contained OM-4, Kaopaque, and #6 Tile. I deflocculated with
Sodium Silicate. It cast beautifully and I had no deflocculation probems.
Yes Darvan 811 is very good, especially for porcelain, but at the time,
1984, my local supplier did not carry Darvan
Now I prefer to spend my time making pots instead of making clay so I just
use the commercial clay bodies. Duncan makes a ^6 stoneware that works
really well and is relatively cheap and it deflocculates easily with sodium
silicate.
Jeff Longtin
Complex Molds Made Easy
612 824 5939
-----Original Message-----
From: Ceramic Design Group [mailto:info@CERAMICDESIGNGROUP.NET]
Sent: Friday, February 15, 2002 2:09 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Epson Salts in Clay bodies
> How come some deflocced slips work just fine and some don't - what else
> could be the answer?
>
Ron and others:
By "slips" I'll assume that discussion centers on casting slips.
Otherwise, I would use the word "engobe" or under-glaze to avoid any
confusion.
I deal with formulating casting slips both for our production as well as
consulting for others.
There are clays that are really poor choices for casting slips. There are
other clays that are my top ten or so for the best clays to use in casting
slips. Clay companies work very hard at blending their products from the
mine into the correct particle sizes for casting.
So one answer to Ron's question is that some clays deflocculate better
because they are specifically blended for that purpose. For instance, I
would not use OM-4 in a casting body. It can be deflocculated, but is a very
poor performer in a casting body. Plus it is full of all sorts of junk, but
that discussion is for another time. Casting depends on the presence of
organics to promote gelling which allows a clay/water mix to cast
successfully. Also, there are kaolins that are better performers than
others. Its all about particle size and gelling.
Another answer to Ron's question is that the choice of the CORRECT
deflocculant is critical.
I stay away from sodium silicate and soda ash. They are quite strong and
have a very short working range before they can thixoid a slip in a minute!
(how's that for making a very verb from an adjective/adverb) Plus soda ash
and sodium silicate really beat the heck out of plaster molds.
My preference is Darvan 811, one of the sodium polyacrylates from RT
Vanderbilt. It is a chained polymer that has a very broad working range and
requires very little to deflocculate a casting slip. It doesn't have a
negative effect on the casting molds either. We also use a bit in our glazes
to get the correct poise.
I'll not add to the discussion of epsom salts to a plastic claybody other
than my preference is to select the correct clays from the get go, and use
soem bentonite or macaloid. They really work wonders and I really don't care
about whether the body is alkaline or acidic or care to change that balance.
I'd rather use clays.
Jonathan
--
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
infor@ceramicdesigngroup.net www.ceramicdesigngroup.net
(use PO BOX for all USPS correspondence)
970 879-9139
Plant Location
1280 13th Street
Steamboat Springs CO 80487
(use PLANT LOCATION for all UPS, Common Carrier, and Courier deliveries)
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