Brenda Funk on fri 20 aug 04
I've used some of my other glaze colorant additions to the base glazes in
Mastering C6 glazes, including bentonite. John and Ron, I never see
bentonite in your colorants and I'm wondering what its purpose is. I know
that its addition to clay makes it more plastic, but I often see it listed
as an addition along with colorants in glaze recipes. I did add the
colorants for "Blue Hare's Fur" to the glossy base #2, and it is one of my
favorites, without the inconsistent results of the original. I'm just
wondering if I can leave out the bentonite.
Thanks, glaze gurus.
Brenda
Megan Ratchford on sat 21 aug 04
"I'm just wondering if I can leave out the bentonite."
Hi Brenda,
Bentonite is not a colorant but helps the glaze components stay in
suspension in the mix. Too little bentonite and the parts of the glaze
settle right to the bottom, too much and it does the same. I'd say that Ron
and Roy have their glazes balanced good enough to leave out the bentonite.
Just stick with the oxides and carbonates as you color your glazes.
Megan Ratchford
Just moved to Lincoln, NE and ready to start the last leg of my BFA after
being in school longer than most doctors!!!!
Earl Brunner on sat 21 aug 04
Bentonite is added as you say, to aid in suspension, since it is not
actually part of the recipe it is often listed with the colorants. If a
glaze has enough clay in it, (ball clay, kaolin, etc,) it often will not
need the addition of bentonite. However, if the glaze has a lot of frit in
it, it might need some additional bentonite. The frits tend to settle out
rather quickly.
Earl Brunner
Las Vegas, NV
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Megan Ratchford
Sent: Saturday, August 21, 2004 7:29 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Bentonite in glazes
"I'm just wondering if I can leave out the bentonite."
Hi Brenda,
Bentonite is not a colorant but helps the glaze components stay in
suspension in the mix. Too little bentonite and the parts of the glaze
settle right to the bottom, too much and it does the same. I'd say that Ron
and Roy have their glazes balanced good enough to leave out the bentonite.
Just stick with the oxides and carbonates as you color your glazes.
Megan Ratchford
Just moved to Lincoln, NE and ready to start the last leg of my BFA after
being in school longer than most doctors!!!!
Richard Aerni on sat 21 aug 04
I'm still sticking with my original reply to this post. Bentonite _is_ an
aid to good glaze suspension, but in my experience, it also keeps the
glazes from powdering so much that they come off when the glazed ware is
handled.
To explain, I had one particular slip glaze that I used to use on the
underside of bowls and platters. I always add bentonite to my glazes,
since I single fire, but in this case, the glaze being predominately slip,
I did not. I began to notice over the course of a number of firings that I
was having spots on the undersides of pieces where the glaze was visibly
thinner, and that they corresponded to finger and handprints. Puzzled, I
spent some time pondering this, and the next firing I mixed the same glaze,
but with 2% bentonite. The problem has not happened since. Yes, I
understand this is purely empirical, anecdotal evidence, but I'll take
practice over theory in this instance.
Best,
Richard Aerni
Rochester, NY
On Sat, 21 Aug 2004 09:43:57 -0700, Earl Brunner wrote:
>Bentonite is added as you say, to aid in suspension, since it is not
>actually part of the recipe it is often listed with the colorants. If a
>glaze has enough clay in it, (ball clay, kaolin, etc,) it often will not
>need the addition of bentonite. However, if the glaze has a lot of frit in
>it, it might need some additional bentonite. The frits tend to settle out
>rather quickly.
John Hesselberth on sat 21 aug 04
On Friday, August 20, 2004, at 10:32 PM, Brenda Funk wrote:
> I've used some of my other glaze colorant additions to the base glazes
> in
> Mastering C6 glazes, including bentonite. John and Ron, I never see
> bentonite in your colorants and I'm wondering what its purpose is. I
> know
> that its addition to clay makes it more plastic, but I often see it
> listed
> as an addition along with colorants in glaze recipes.
Hi Brenda,
Bentonite in glazes is used to help keep glazes in suspension. We tried
to include enough clay in our glazes that they do pretty well on their
own without adding bentonite. There are one or two, though, that will
hard pan on long sitting and would probably benefit from 1-2% bentonite.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ron Roy on sun 22 aug 04
Hi Brenda,
If you care to send me the original glaze I will explain why the bentonite
was there - or should not have been there.
Usually it's in a glaze to help suspend the glazes during the glazing
process. If there is not enough raw clay in the glaze, or the clay is the
wrong kind, or there are materials like Neph Sy that deflocculate the slop
- then adding bentonite will help the glaze stay suspended longer.
Many times I see bentonite included in a recipe when it is not needed as
well. Perhaps the maker included it because it helped with another glaze so
includes it in all glazes now.
As others have pointed out - bentonite helps reduce powdering of raw glaze
- especially those using kaolin in the recipe - it works.
I have used it to stop crawling in a glaze - I have also used a
substitution of ball clay for kaolin to stop crawling.
Our glossy base 2 has 17% EPK - so I would expect that glaze to stay
stirred very well - however - if you found the dry glaze was to powdery you
can add bentonite to help stop that. I could also reformulate the glaze to
use ball clay instead of kaolin - which would have the same effect.
All I need is the kind of ball clay you would use.
RR
>I've used some of my other glaze colorant additions to the base glazes in
>Mastering C6 glazes, including bentonite. John and Ron, I never see
>bentonite in your colorants and I'm wondering what its purpose is. I know
>that its addition to clay makes it more plastic, but I often see it listed
>as an addition along with colorants in glaze recipes. I did add the
>colorants for "Blue Hare's Fur" to the glossy base #2, and it is one of my
>favorites, without the inconsistent results of the original. I'm just
>wondering if I can leave out the bentonite.
>
>Thanks, glaze gurus.
>
>Brenda
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on sun 22 aug 04
Too much bentonite will not make a glaze settle out - it can make the glaze
shrink too much during drying and cause crawling however.
The usual warning is 2% is enough - over that and you take your chances.
Adding a flocculant like Epsom Salts will help stop a glaze from settling
out but too much will make it settle again.
The right amount of soda ash will deflocculate a glaze - make it settle out
- use more and the effect is reversed.
RR
> Bentonite is not a colorant but helps the glaze components stay in
>suspension in the mix. Too little bentonite and the parts of the glaze
>settle right to the bottom, too much and it does the same.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Snail Scott on sun 22 aug 04
At 10:32 PM 8/20/2004 -0400, you wrote:
>...I never see
>bentonite in your colorants and I'm wondering what its purpose is. I know
>that its addition to clay makes it more plastic, but I often see it listed
>as an addition along with colorants in glaze recipes...
It has no effect on color; it is added as
a suspension agent, especially in glazes
with low percentages of clay (which helps
with suspension) or high percentages of frit
(which is notoriously hard to keep suspended).
Bentonite is generally listed separately from
the main recipe, together with the colorants,
because it is an additive, and not integral to
the chemistry of the glaze. Keeping these
components separate allows the essentials of
the recipe to be compared more easily to other
recipes. It also allows easier 'tinkering'
with the chemistry. Since the essential
materials are typically made to add up to 100%,
variations in percentages of additives do not
force changes in the other percentages.
For example, if additives were included in a
recipe:
If a base recipe has, say 50% frit with no
colorants, and you want to add 10% iron, you
will end up with only 45% kaolin, but if you
add 2% cobalt instead, you'd have 49% kaolin,
but the base recipe would still be the same in
both cases. The same principal applies to
bentonite, CMC, and other additives: you don't
want to have to recalculate the whole recipe
just because you decide to try 1% of bentonite
instead of 2%, or whatever. So, additives are
usually written and added separately from the
100% base recipe, which remains unaffected
mathematically. Much easier!
Without bentonite, glazes that are low in clay
or high in frit tend to settle to the bottom
of their container. Bentonite is not essential,
but without it, such glazes will need to be
stirred often (sometimes VERY often) to stay
mixed. If you can live with that, you may be
able to skip the bentonite, or at least use
less, but one session of scraping a badly
settled glaze from the bottom of a bucket can
make a little bentonite seem like a really
great idea!
-Snail Scott
David Beumee on sun 22 aug 04
Megan wrote:
Bentonite is not a colorant but helps the glaze components stay in
suspension in the mix.
It is true that betonite helps keep glazes in suspension, particularly those with little or no clay content, but fusion button tests prove that most commercially available bentonites are loaded with iron and burn chocolate brown at cone 10. In a celedon glaze over porcelain this can mean quite alot of iron spotting. Their are "beneficiated" bentonites available, such as Veegum T that burn white, and a straight across substitution of 1 or 2% for bentonite should float a glaze with no clay content. If not, you can make a saturated solution of Epsom Salts by adding a quart of hot water in a blender (designated for the studio) and slowly adding magnesium sulfate (epsom salt) crystals to the water and mixing. You can keep a container of this solution in the studio and add a tablespoon or two to a 10000 gram batch of glaze to keep glazes from settling (hard panning).
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> "I'm just wondering if I can leave out the bentonite."
>
> Hi Brenda,
> Bentonite is not a colorant but helps the glaze components stay in
> suspension in the mix. Too little bentonite and the parts of the glaze
> settle right to the bottom, too much and it does the same. I'd say that Ron
> and Roy have their glazes balanced good enough to leave out the bentonite.
> Just stick with the oxides and carbonates as you color your glazes.
>
> Megan Ratchford
> Just moved to Lincoln, NE and ready to start the last leg of my BFA after
> being in school longer than most doctors!!!!
>
> ______________________________________________________________________________
> 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.
Snail Scott on mon 23 aug 04
At 10:45 PM 8/22/2004 -0500, I wrote:
>If a base recipe has, say 50% frit with no
>colorants, and you want to add 10% iron, you
>will end up with only 45% kaolin, but if you
>add 2% cobalt instead, you'd have 49% kaolin,
>but the base recipe would still be the same in
>both cases.
Dumb typo! Of course I meant frit, not kaolin,
throughout (or else the other way around).
Wonder where my brain was? Sorry.
-Snail
Cynthia Bracker on wed 25 aug 04
Macaloid is also a good substitution for Bentonite and is very pure and
white. You might also check with your supplier to see what bentonite
they sell. "Western Bentonite" is generally good quality. I've not
seen iron spotting from it.
Cindy Bracker
David Beumee wrote:
> most commercially available bentonites are loaded with iron and burn chocolate brown at cone 10. In a celedon glaze over porcelain this can mean quite alot of iron spotting. Their are "beneficiated" bentonites available, such as Veegum T that burn white, and a straight across substitution of 1 or 2% for bentonite should float a glaze with no clay content.
>
David Beumee on thu 26 aug 04
"Western Bentonite" is generally good quality. I've not
> seen iron spotting from it.
We must be using different sources of western bentonite. The western bentonite available through our Denver supplier is loaded with iron and burns a dark chocolate brown at cone 10 in reduction. For use in a tenmoku glaze, this makes little or no difference. It's a different story with a celedon glaze over a porcelain body, where the use of any percetage of western bentonite causes iron spotting to occur.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Macaloid is also a good substitution for Bentonite and is very pure and
> white. You might also check with your supplier to see what bentonite
> they sell. "Western Bentonite" is generally good quality. I've not
> seen iron spotting from it.
> Cindy Bracker
>
>
> David Beumee wrote:
>
> > most commercially available bentonites are loaded with iron and burn chocolate
> brown at cone 10. In a celedon glaze over porcelain this can mean quite alot of
> iron spotting. Their are "beneficiated" bentonites available, such as Veegum T
> that burn white, and a straight across substitution of 1 or 2% for bentonite
> should float a glaze with no clay content.
> >
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy on fri 27 aug 04
At Tuckers we tested the various bentonites - in Porcelain bodies.
Some bentonites has some specking - other did not.
The main thing was - there was no decernable difference between Bentonite
and Macaloid in terms of whitness of the clay body.
The bentonite analysis I have says 3.67% iron - usually only 2 % per 100
lb. is used in a body. So you are adding 0.74 iron to the body - the
whitest Kaolin is EPK and it has about 0.7 iron. Would anyone notice that?
What is the analysis for Macaloid?
RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
David Beumee on sat 28 aug 04
Ron wrote,
At Tuckers we tested the various bentonites - in Porcelain bodies.
Perhaps the bentonites tested at Tucker's were of different origin than the bentonites I have tested. I'm sure that at a 2% addition in a porcelain body the effect of an iron bearing content would be less than in a clear or celedon glaze used over porcelain.
> The main thing was - there was no decernable difference between Bentonite
> and Macaloid in terms of whitness of the clay body.
Again, perhaps your sources were different. The bentonites that I have tested from Mile High, Archie Bray Foundation and Laguna, including L-10, what Laguna advertises as their whitest burning bentonite, are so loaded with iron that they all burn a dark chocolate brown as fusion button tests at cone 10 in reduction. Don't take my word for it Ron. Do the tests yourself. If you get some results that show that a bentonite exists that burns white in reduction at cone 10, let me know. I'll be glad to find out your results, and glad to use it, because bentonite sells for a bunch less than Macaloid, Bentone MA, or Veegum T. In the mean time I've tested Macaloid and Veegum T and Bentone MA as fusion button tests and I know they burn white, and I'll continue to pay for them because they do not color either my clay or my glazes.
If you have some analysis on a bentonite that shows 3.67 % iron, let me know what it is. I'll be glad to know and happy to order some to test.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> At Tuckers we tested the various bentonites - in Porcelain bodies.
>
> Some bentonites has some specking - other did not.
>
> The main thing was - there was no decernable difference between Bentonite
> and Macaloid in terms of whitness of the clay body.
>
> The bentonite analysis I have says 3.67% iron - usually only 2 % per 100
> lb. is used in a body. So you are adding 0.74 iron to the body - the
> whitest Kaolin is EPK and it has about 0.7 iron. Would anyone notice that?
>
> What is the analysis for Macaloid?
>
> RR
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> 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.
David Beumee on sun 29 aug 04
Hi John,
Unfortunately my computer would not let me open link you sent. Where can I send for samples of Standard Bentonite or Bentonite L?
I'm trying to forget your first post. I can assure you I know the difference between bentonite and Barnard Clay.
David Beumee
> David,
>
> We are using standard bentonite and have done melt tests to cone 10 in
> reduction and it does not fire brown. (3.5% Fe)
>
> http://ceramic-materials.com/cermat/area.php?
> area=1&id=106&site=cermat&skin=cermat&
>
> I believe it is called Standard Bentonite.
>
> You could also get Bentonite L.
>
>
> http://ceramic-materials.com/cermat/area.php?
> area=1&id=104&site=cermat&skin=cermat&
>
> Good Luck,
>
> John Britt
> www.johnbrittpottery.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.
John Britt on sun 29 aug 04
David,
I don't know if anyone has mentioned this, but it sounds like you have
Barnard Slip (Blackbird). That really burns brown in a reduction melt test.
In the raw state (unfired) my bentonite is greenish while the barnard is
light brown.
Just wondering,
John Britt
www.johnbrittpottery.com
John Britt on sun 29 aug 04
David,
We are using standard bentonite and have done melt tests to cone 10 in
reduction and it does not fire brown. (3.5% Fe)
http://ceramic-materials.com/cermat/area.php?
area=1&id=106&site=cermat&skin=cermat&
I believe it is called Standard Bentonite.
You could also get Bentonite L.
http://ceramic-materials.com/cermat/area.php?
area=1&id=104&site=cermat&skin=cermat&
Good Luck,
John Britt
www.johnbrittpottery.com
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