Victoria E. Hamilton on wed 22 dec 04
Geoffrey -
I had a similar problem with a peach shino I use.
Put a small amount bentonite (200 gms maybe) in a jar with a small amount of
water and shake it up well to saturate the bentonite. Then pour it in the
glaze. Mix well and sieve.
Vicki Hamilton
Millennia Antica Pottery
Seattle, WA
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Geoffrey
Barst
Sent: Wednesday, December 22, 2004 17:19
To: CLAYART@LSV.CERAMICS.ORG
Subject: Settling in glaze
I have recently tested some new glazes and mixed up 5000 gm batches. A
couple of them settle amazingly fast, needing constant stirring right up
to the second the pot is dipped. After one day the glaze has settled to
the consistency of thick clay at the bottom of the bucket & I even tore my
nail while hand mixing it. What can I add at this stage to improve the
settling without altering the fired results?
Geoff Barst
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Geoffrey Barst on wed 22 dec 04
I have recently tested some new glazes and mixed up 5000 gm batches. A
couple of them settle amazingly fast, needing constant stirring right up
to the second the pot is dipped. After one day the glaze has settled to
the consistency of thick clay at the bottom of the bucket & I even tore my
nail while hand mixing it. What can I add at this stage to improve the
settling without altering the fired results?
Geoff Barst
Vince Pitelka on thu 23 dec 04
> It sounds as though your recipe contains very little clay. Bentonite will
> not work unless there is enough clay to flocculate, so I guess I would try
> CMC or Vee Gum.
Cindy -
I am wondering about the above. Bentonite has no affect on flocculation or
deflocculation, since it is just clay. So bentonite will help to combat
settling problems whether or not there is any other clay in the recipe.
Also, when mentioning Veegum, it is important to specify Veegum-T or
Veegum-Cer. Veegum-T is just a refined bentonite, and works pretty much the
same as bentonite in a glaze but is much more expensive. Veegum-Cer
contains refined bentonite as well as CMC gum, and works well for thickening
glazes.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
John Britt on thu 23 dec 04
Goeff,
Glazes that act like that usually benefit from a tablespoon of Epsom Salts.
That type of settling indicates that the glaze is deflocculated.
You can test it by putting about two cups of the glaze in a container and
adding Epsom Salts slowly. If it thickens you then know that that is the
solution.
Shino glazes should never need bentonite because they are composed of up to
40% clay which suspends very well. Usually it is the soluble soda ash in
the glaze that is causing the deflocculation.
Hope it helps,
John Britt
www.johnbrittpottery.com
Dorie Mickelson on thu 23 dec 04
Geoff -- You can add what one of my teachers calls "magic goop" to your
glazes to fix this problem. Take one quart hot water and add three
tablespoons CMC and one tablespoon bentonite to it and mix it in a
blender for several minutes. This will produce a nice thick gelatinous
mixture, from which you can add about one half cup to one cup of magic
goop (the measurements do not need to be ultra precise) to each of your
glazes that tend to settle out. Just decant some clear water off the
glaze first to offset the water you are adding back in with the magic
goop.
If your glazes have already settled out into a solid rock at the bottom
of your glaze bucket, however, you will first need to pour off the clear
water and use a big metal or wooden spoon or like instrument to break up
the settled out glaze, and then take the pieces of glaze in your hands
(wearing latex gloves) and break them up further into smaller pieces.
Add some of the water back in (not all of it) and mix it with a jiffy
mixer (if you've got one) and gradually add the magic goop in. Then
slowly add the clear water back in and mix it all together until it
reaches the right consistency -- you should not need to add all of the
water back in though since the magic goop replaces some of the water (if
you do add it all in, your glaze may end up being too thin, but of
course it depends on how thick or thin your glaze was to begin with).
I've done this successfully with no changes to glaze color or firing
results -- it is a big pain in the butt if the glaze has already settled
out into a rock hard mass but once you go through this process, the
cmc/bentonite keeps the chemicals in suspension and you should not have
settling out problems with that glaze again. I have heard that the
magic goop can sometimes produce an unpleasant smell in the glaze over
time, but I've not yet encountered that problem...hope that helps!
Dorie Mickelson in Ann Arbor, Michigan, where we woke up this morning to
about ten inches of fluffy white snow!
www.FreeSpiritCreations.com
From: Geoffrey Barst
Subject: Settling in glaze
I have recently tested some new glazes and mixed up 5000 gm batches. A
couple of them settle amazingly fast, needing constant stirring right up
to the second the pot is dipped. After one day the glaze has settled to
the consistency of thick clay at the bottom of the bucket & I even tore
my nail while hand mixing it. What can I add at this stage to improve
the settling without altering the fired results?
Geoff Barst
Ron Roy on thu 23 dec 04
Hi Geoff,
Best thing to do is sub in materials that will stop that - it is usually
possible.
Send me a couple of recipes and I'll try. Let me know what ball clays you
have on hand.
RR
>I have recently tested some new glazes and mixed up 5000 gm batches. A
>couple of them settle amazingly fast, needing constant stirring right up
>to the second the pot is dipped. After one day the glaze has settled to
>the consistency of thick clay at the bottom of the bucket & I even tore my
>nail while hand mixing it. What can I add at this stage to improve the
>settling without altering the fired results?
>
>Geoff Barst
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Cindy on thu 23 dec 04
Dear Geoff,
It sounds as though your recipe contains very little clay. Bentonite will
not work unless there is enough clay to flocculate, so I guess I would try
CMC or Vee Gum. These organic suspending agents will eventually "go bad" and
make your glaze smell, well, bad . Beyond that, I don't think they have any
ill effects.
You have to mix them with water and let them sit long enough to hydrate
fully before adding to a glaze--probably between 2-5%. I would add a little
at a time until you get the results you want. I don't like glazes without
clay for the very reasons you mention, so I haven't tried this myself, but
this is the advice I have seen given by others. I hope it helps.
Merry Christmas,
Cindy in SD
Edouard Bastarache Inc. on thu 23 dec 04
John,
" Shino glazes should never need bentonite because they are composed of up
to
40% clay which suspends very well. Usually it is the soluble soda ash in
the glaze that is causing the deflocculation.
John Britt"
I am a floculation-freak, I always add 3% bentonite in my Shino glazes
and some Epsom salt "ad libidum", and I am 100% satisfied with this
approach.
Later,
"Ils sont fous ces quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
Daniel Semler on thu 23 dec 04
Hi Ron,
This sounds like an interesting and useful trick.
Is this mainly a matter of trying to increase fine particle clay content ? or
is there a little more to it than that ?
> Best thing to do is sub in materials that will stop that - it is usually
> possible.
>
Thanx
D
John Britt on thu 23 dec 04
Edouard,
Of course I am not telling anyone what to do. I am aware that there
multiple approaches, that is what makes life and clayart interesting.
As you know clay has natural suspension properties and so it follows that
if a recipe has over 20% clay then you "should not" need bentontite because
the clay in the recipe will be doing the job. But if you want to use it
then OK.
But if a recipe has low clay, like copper reds or other low alumina glazes,
or high feldspar glazes, then adding bentonite will help and the Epson Salt
will flocculate slop.
Good Luck,
John Britt
www.johnbrittpottery.com
Ron Roy on fri 24 dec 04
Hi Daniel,
First step is to take out Kaolin and replace with a Ball clay - preferably
one with a high shrinkage as they tend to suspend better - Bell Dark is my
favorite but I usually have to go with something like OM#4. Because ball
clay has less alumina and you keep the alumina mols the same - you have to
use more ball clay - and reduce the silica because ball clay has more.
Then adding bentonite because it works better with a ball clay
Ball clays and bentonites have a higher surface strength than kaolin so you
also cure dusting at the same time.
Some will say ball clays have more iron and it will affect the colour - not
often but - in that case perhaps a combination of ball and kaolin will do -
it depends on how much ball clay - and if you have a lot you probably don't
have deflocculation of the glaze slop - and you can afford to replace some
of it with Kaolin.
Cutting back on those materials that will deflocc - like Neph Sy and
Lithium carb - replacing with spar and Spodumene.
Replacing a frit that has alumina with one that does not lets you put more
clay in. This is very helpful at cone 6 because so many cone 6 glazes have
a fair amount Neph Sy in them.
If all that does not work then adding a small amount of Epsom salts will
usually do it.
Some local water tends to be to acidic and that can contribute - if worse
comes to worse - then using distilled or deionized water is worth a try.
It is always best to cure the problem by changing the recipe first - adding
solubles can present problems.
Understanding your materials is necessary - beware those with high amounts
of sodium - the alkalies like Sodium and Lithium will deflocc clay or glaze
if they go into solution - and it does not take much.
One of my favorite tricks - when lowering expansion to cure crazing is to
take out spar or neph sy - lowering the KNaO to reduce the expansion - when
you do that you take out alumina and silica - which gives room for more
clay - which improves suspension.
Trying to do all those things without calculation is impossible of course -
trying to guess how much ball to use to replace the kaolin from the amounts
in the recipe is going to be a real guessing game. I can do it better now
because I have done it so many times using calculation - getting the
alumina right is fairly easy - but how much silica to remove is not so
easy.
RR
> This sounds like an interesting and useful trick.
>
> Is this mainly a matter of trying to increase fine particle clay content ? or
>is there a little more to it than that ?
>
>> Best thing to do is sub in materials that will stop that - it is usually
>> possible.
>D
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on sat 25 dec 04
Dear Vince,
If, as you say, "Bentonite has no affect on flocculation or
deflocculation, since it is just clay", why is there any need to use
it as a glaze additive ? It would be an expensive substitute for
Kaolin or Ball Clay.
It is my understanding that, except for the clay minerals, all
insoluble ingredients, be they natural minerals, frits, raw chemicals
or ash, settle rapidly and can be neither flocculated nor
deflocculated. They settle rapidly because they have low surface area
to volume and a density at least two and a half times that of Water..
Density will be higher in the case of Titanium minerals and Lead
compounds.
Stokes Law, which relates the various attributes of a body falling in
a viscous medium, may enable interested people calculate the rate of
settling of their own glazes, in an approximate fashion. An additional
thought is that when the force dragging particles down becomes equal
to that of buoyancy forcing them up the material will not settle.
No, Clay........ Sorry, have been called to Duty with the Carver set.
Best regards and good wishes for the coming year,
Ivor Lewis.
Redhill,
S. Australia.
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