Earl Brunner on mon 7 jun 99
I have been testing a series of cone 5-6 glazes from Clay and Glazes by
James Chappell.
SG22 is described as a Opaque White Gloss Glaze. With the chemicals I
have it comes out mat, a nice mat Cobalt is a nice purple, I was
looking for a violet a few weeks ago.
This mat isn't what I was looking for but had possibilities. Tests
looked good so I mixed up a larger batch. The first firing with the
larger batch had one pot that shivered badly on the rim (The greenware
pot had oxide design, it shivered ove the oxide). There were at least
three pots in the firing that broke from what appears to be compression
stress. I think I need to increase the expansion of the glaze without
changing the appearance much.
Silica 45.7
Epk 16.8
Calcined kaolin 7.2
Lithium Carb 10.8
Magnesium carb 10.1
whiting 9.4
any suggestions?
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Thonas C. Curran on tue 8 jun 99
Earl Brunner wrote:
>
> ----------------------------Original message----------------------------
> I have been testing a series of cone 5-6 glazes from Clay and Glazes by
> James Chappell.
> SG22 is described as a Opaque White Gloss Glaze. With the chemicals I
> have it comes out mat, a nice mat Cobalt is a nice purple, I was
> looking for a violet a few weeks ago.
> This mat isn't what I was looking for but had possibilities. Tests
> looked good so I mixed up a larger batch. The first firing with the
> larger batch had one pot that shivered badly on the rim (The greenware
> pot had oxide design, it shivered ove the oxide). There were at least
> three pots in the firing that broke from what appears to be compression
> stress. I think I need to increase the expansion of the glaze without
> changing the appearance much.
>
> Silica 45.7
> Epk 16.8
> Calcined kaolin 7.2
> Lithium Carb 10.8
> Magnesium carb 10.1
> whiting 9.4
>
> any suggestions?
> --
> Earl Brunner
> http://coyote.accessnv.com/bruec
> mailto:bruec@anv.net
Earl: Lithium carbonate has low coefficient of expansion...is probably
the culprit. Try decreasing it and adding more of the other fluxes.
Good luck, CNC punchy at 1:30am on hot night!
Craig Martell on tue 8 jun 99
Hello Earl:
>----------------------------Original message----------------------------
>I have been testing a series of cone 5-6 glazes from Clay and Glazes by
>James Chappell.
>SG22 is described as a Opaque White Gloss Glaze
>The first firing with the larger batch had one pot that shivered badly on
>the rim
>Silica 45.7
>Epk 16.8
>Calcined kaolin 7.2
>Lithium Carb 10.8
>Magnesium carb 10.1
>whiting 9.4
I haven't been able to use Insight lately so I didn't calculate the
expansion for this glaze but with lithium as the main fluxing oxide and
magnesium, which is of lower expansion than soda or potash, this glaze is
going to have a low expansion number. Try blending some potash, or soda
feldspar with this glaze. Also, maybe some nepheline syenite which has the
highest expansion of the three.
Craig Martell in Oregon
Donna Torrance on fri 23 nov 07
I hate to admit it but I am the queen of shivering. A school delema for
years. Sandblasting is the only real cure I know, but how to avoid it, is
to thin that 06 glaze to almost water. They do sell dipping glazes, but
even those need to be thinned with at least a gallon of water per five
gallons or you will still get shivering...I would rather have it come out
too thin and re-glaze rather than throw work away. Reglazing a shivered
piece causes more shivering. Lots of student heartaches. Trust me, I've
tried everything.
Vince Pitelka on fri 23 nov 07
Dona Torrance wrote:
>I hate to admit it but I am the queen of shivering. A school delema for
> years. Sandblasting is the only real cure I know.
Hi Donna -
I am a lilttle concerned about your comment above. If we are talking about
true shivering, which is the result of a fairly extreme disagreement in
expansion/contraction rates between the claybody and the glaze, the real
danger is that those razor sharp slivers of glaze that separate from the
rims and high spots can continue to appear months or years after firing, and
needless to say, they can be very dangerous. The only safe solution with
any functional pot that displays shivering is with the hammer. Every piece
showing shivering must be destroyed.
The solution to the problem is a whole different issue. If you are working
with commercially made clays and glazes, it is really up to your supplier to
identify and solve the problem. If you are mixing your own clay and/or
glazes, you can solve the problem yourself. Shivering is the result of
excess glaze compression. A slight amount of glaze compression (where the
firing shrinkage of the claybody is every so slightly greater than the
glaze) is a good thing, and results in a more resilient, durable fired
piece. But if glaze compression is exessive, we get shivering. I had a
very bad experience with shivering when I was a full-time studio potter. I
was using commercially made clay (Westwood Rod's Bod), but was mixing my own
glazes, so I just reduced the silica content of the problem glaze very
slightly (about 0.5%), which increased the shrinkage very slightly, and
completely eliminated the problem.
So the question is, are we really talking about true shivering in the work
you are referring to? Is this work midrange or high-fired? Is the glaze
coming off in razor-sharp slivers along the rims and ridges? If so, there
are people on this list who will be happy to help you find a solution to the
problem. This is not something you want to put up with over time.
Good luck -
- 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/
Snail Scott on sat 24 nov 07
On Nov 23, 2007, at 11:00 PM, Automatic digest processor wrote:
> Date: Fri, 23 Nov 2007 09:13:07 -0500
> From: Donna Torrance
> Subject: shivering
>
> ... how to avoid it, is
> to thin that 06 glaze to almost water. They do sell dipping glazes,
> but
> even those need to be thinned with at least a gallon of water per five
> gallons or you will still get shivering...
If you are getting consistent shivering with multiple
commercial glazes, it sounds like you are using a
very unsuitable clay body.
Shivering is caused by a fundamental incompatibility
between the clay body and the glaze - differing
coefficients of expansion. The glaze and clay shrink
as they cool after firing, and if the clay shrinks more than
the glaze, you will get shivering. (The opposite is crazing -
more common but less devastating.) It is rooted in the
chemistry of the materials. Watering it down or thinning
it will not cure it. It will simply be less evident if the glaze
is thin.
Thin glazes become a mixture of the glaze and the clay
body underneath, as the glaze slightly fluxes the surface
clay and draws the clay materials (including alumina) into
the glaze mix, creating a new glaze recipe in situ. That's
why thin glazes can sometimes look radically different
from the same glaze at a more standard thickness.
Many commercial glazes are less subject to this effect,
but that's part of the reason they're boring.
As a means to avoid shivering, thinning is of limited utility,
since not all glazes look the same when thin (i.e. mixed
with the clay body) and if the glaze is applied very thinly, it
probably won't serve you the way you wanted the glaze to
in the first place, with smooth, substantial coverage. Better
to change glazes, or (if it's a frequent occurrance) clays.
-Snail
tonya Johnson on sun 25 nov 07
Snail,
Thank you so much for the suggestions. All are appreciated. But I do not
have shivering. It is true blistering. And I mix all my own glazes by recipe.
And it is only the one glaze that is blistering. But I am printing out all
suggestions to consider : ) Tonya
**************************************Check out AOL's list of 2007's hottest
products.
(http://money.aol.com/special/hot-products-2007?NCID=aoltop00030000000001)
Vince Pitelka on fri 2 dec 11
Susannah Biondo-Gemmel wrote:
"We are suddenly having major issues with shivering with cone 10 reduction
stoneware and glazes that we have used for years. Does anyone have any
ideas what might be causing this???
Hi Susannah -
Having experienced the same when I was a full-time potter in the early
1980s, I can appreciate what a nightmare this is. Have you recently starte=
d
using a new batch of Custer as the potash spar in your glazes, or did you
recently change from the old G-200 to the HP? Either of those would make
your glazes more refractory and change expansion and broaden the
differential between the glaze and your claybody, increasing tension and
causing those razor-sharp slivers to pop off. When that happens, it
increases tension at the interface and can cause shivering. When it
happened to me, I was using Rod's Bod from Westwood Clay Company (absorbed
by Laguna). I was doing lots of work with oxides and a clear glaze, so mos=
t
of my work depended on that clear glaze. That's the one that shivered. It
happened on an entire 100-cubic-foot kiln load that had to be destroyed. I
contacted Westwood and they told me to give them the formula for my glaze.
I did and someone did some calculations, called me back, and told me to
increase the barium carbonate. I did that and ended up with the next
100-cubic-foot-load of pots a classic barium mat that was all wrong for my
work. No shivering, but certainly not an acceptable solution. Their
suggestion baffles me to this day, because it just doesn't make sense. At
that point I did the research I should have done to begin with, and
somewhere I found a suggestion that a very slight reduction in alumina coul=
d
solve Shivering. In the original recipe I simply swapped half the kaolin
for ball clay, thus slightly reducing the alumina contact, and ended up wit=
h
a fairly perfect satin gloss with no shivering or crazing. Of course this
is no indication that the solution will be the same for you.
I never did find out what caused the change - no idea whether it was a
change in the claybody, or a change in one of my glaze materials. This is
what we face in ceramics. For the most durable, food-safe glazes with no
crazing, we want them to be under slight compression, and that pushes thing=
s
pretty close to the edge. Any change that makes the claybody a little more
refractory or the claybody a little less can increase the compression enoug=
h
to cause failure at the clay-glaze interface, i.e. shivering. It is one of
the potters greatest nightmares.
If this is suddenly happening to all your glazes, and if my suggestion abou=
t
the potash feldspar does not apply, then it seems most likely to be a chang=
e
in the claybody. Is there any chance that this happened with a new shipmen=
t
of clay? Or if you mix your own clay, did it happen with a new shipment of
some raw material?
I am just tossing out ideas here. I wish I had a better answer for you. I
have been there.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net
http://iweb.tntech.edu/wpitelka/
Susannah Biondo-Gemmell on fri 2 dec 11
We are suddently having major issues with shivering with cone 10 reductio=
=3D
n=3D20
stoneware and glazes that we have used for years. Does anyone have any=3D2=
0=3D
ideas what might be causing this???
Thanks for any input!
Susannah
Steve Mills on sat 3 dec 11
First off.=3D20
To me one of two things have changed:
The clay body you are using has changed and is shrinking more.=3D20
or
(less likely) The same has happened to your glaze but it's shrinking LESS!
Do you make either your Body or your Glaze or are they bought in?
Steve M
Steve Mills
Bath
UK
www.mudslinger.me.uk
Sent from my Ipod touch
On 2 Dec 2011, at 18:14, Susannah Biondo-Gemmell =
w=3D
rote:
> We are suddently having major issues with shivering with cone 10 reductio=
n=3D
=3D20
> stoneware and glazes that we have used for years. Does anyone have any=
=3D20=3D
> ideas what might be causing this???
>=3D20
> Thanks for any input!
>=3D20
> Susannah
Snail Scott on sat 3 dec 11
On Dec 2, 2011, at 12:14 PM, Susannah Biondo-Gemmell wrote:
> We are suddently having major issues with shivering with cone 10 reductio=
n
> stoneware and glazes that we have used for years. Does anyone have any
> ideas what might be causing this?
Changes in your fluxes (either in the clay body or
the glaze) are my usual suspects.
-Snail
Paul Herman on sat 3 dec 11
Hi Susannah,
As others have noted, it's a case of imbalance between the thermal
expansion and contraction of the clay body and the glaze.
First questions are, what changed recently? Do you make your own clay
and or glazes? If you use a premixed wet clay, it could have changed
without your knowledge. As Vince noted, there has been an unwelcome
change in Custer feldspar recently.
We need more information.
Best wishes,
Paul Herman
Great Basin Pottery
Doyle, California US
www.greatbasinpottery.com/
On Dec 2, 2011, at 10:14 AM, Susannah Biondo-Gemmell wrote:
> We are suddently having major issues with shivering with cone 10
> reduction
> stoneware and glazes that we have used for years. Does anyone have
> any
> ideas what might be causing this???
>
> Thanks for any input!
>
> Susannah
Ron Roy on sat 3 dec 11
Hi Susannah,
Probably your clay body - did you start using a new batch before the
shivering started?
I can do a short analysis of the problem - I will need a couple of the
recipes of the glazes that are shivering and a couple of the glazes
that are not. I will calculate the expansions and that should give
valuable clues.
It will not be hard to recalculate shivering glazes in most cases if
they are the problem and the clay can be fixed as well if it's your
own recipe.
If you are mixing your own clay I need to see the recipe for it - if
you buy your clay call your supplier and ask if the problem is
happening elsewhere and if it's custer spar they are using.
This is not a g200 spar problem by the way.
I'll away for a day but can get to work on this Monday.
RR
Quoting Susannah Biondo-Gemmell :
> We are suddently having major issues with shivering with cone 10 reductio=
n
> stoneware and glazes that we have used for years. Does anyone have any
> ideas what might be causing this???
>
> Thanks for any input!
>
> Susannah
>
Edouard Bastarache on sat 3 dec 11
Cures of shivering according to Robin Hopper :
1-Decrerase the silica in either the body or the glaze.
2-Increase the feldspar, especially sodium feldspar or
nepheline syenite , or other alkaline bearing materials.
(The Ceramic Spectrum)
Gis,
Edouard Bastarache
Spertesperantisto
Sorel-Tracy
Quebec
http://www.flickr.com/photos/30058682@N00/
http://edouardbastarache.blogspot.com/
http://edouardbastaracheblogs2.blogspot.com/
http://www.facebook.com/edouard.bastarache
Ron Roy on sun 4 dec 11
Hi Susannah,
Just wondering if you got my message re your shivering problem?
RR
Quoting Susannah Biondo-Gemmell :
> We are suddently having major issues with shivering with cone 10 reductio=
n
> stoneware and glazes that we have used for years. Does anyone have any
> ideas what might be causing this???
>
> Thanks for any input!
>
> Susannah
>
Susannah Biondo-Gemmell on mon 5 dec 11
Thank you everyone for all of the replies! Here is some of the informati=
=3D
on that=3D20
was requested of me.
We are using a cone 10 clay and all cone 10 glazes. Just about every one=
=3D
of=3D20
our glazes are shivering--that is razor sharp pieces popping off on both =
=3D
lips of=3D20
work and on flat planes of the work. All work is fired in reduction.
Our clay body is:
Hawthorn Fireclay- 33
Gold Art- 25
C and C Ball- 25
Custer Feldspar- 7
Silica- 7
Fine Grog- 7
(for the sculpture body also add Medium Grog-7)
This is my second year at this institution and, from what I understand, t=
=3D
his is=3D20
a new issue. Both my sculpture and throwing studens are having issues.
Some of the worst glazes are:
Salt Yellow:
Neph Sye- 60.7
Dolomite- 20
Zircopax- 15.2
C & C Ball Clay- 4.1
Bentonite- 3.8
RIO- .9
Celedon:
Custer- 262
Whiting- 52
Zinc Oxide- 8
Kaolin- 47
Silica- 59
RIO- 8
Bentonite- 1.5
As I said though, all of our glazes are shivering, which makes me think t=
=3D
his is a=3D20
claybody issue. Could it me the Custer? If so, what do I do to remedy t=
=3D
his?
Thank you all so much,
Susannah
David Finkelnburg on tue 6 dec 11
Susannah,
Has the shivering occurred through more than one batch of your clay?
If all your glazes are shivering and have not in the past then whoever
mixed the last batch of clay may have made a mistake with the recipe and
added or failed to add some ingredient so that the clay no longer has the
anticipated coefficient of thermal expansion. You may want to
personally make up a small batch, say 5 pounds total, and fire glazed test
tiles. If the problem is in the batch most recently made, you will know if
the test tiles fire OK. If the tiles don't, then you will know the problem
is with one of the ingredients.
Shivering, as you know, occurs when during cooling the glaze does not
shrink as much as the fired clay, thus putting the glaze in compression.
The glazes you posted are not low expansion glazes. For them to shiver the
most logical explanation is in the batch of clay.
I hope you are able to solve the problem quickly.
Dave Finkelnburg
http://www.mattanddavesclays.com
Paul Herman on tue 6 dec 11
Susannah,
It sounds like a clay body problem to me, especially because you say
it is affecting all the glazes you use.
I'm also very wary of Custer feldspar right now, because of the
information that the formula may have changed, or they may have
produced a "bad" batch. Also because I have been seeing some changes
in my stoneware clay, which could be explained by a weaker alkali
content in the feldspar. My clay body formula contains 10% Custer, and
though I've experienced no shivering or dunting, the clay seems to be
a little dry and under fired.
So in addition to what Dave advises about making up a carefully
measured test batch of your clay using Custer, in addition I advise
you make up a parallel clay body test using a different feldspar like
G-200 or G-200HP if you have either, and examining the difference
between the two fired clay samples.
Yesterday I put some tests in a friend's cone 10 firing, and I will
report back when they are cool. I made fusion buttons of all my
feldspars in stock, and a couple of clay body samples, one with the
old G-200.
Good mixing to all you clay mixers,
Paul Herman
Great Basin Pottery
Doyle, California US
www.greatbasinpottery.com/
On Dec 5, 2011, at 7:38 AM, Susannah Biondo-Gemmell wrote:
> Thank you everyone for all of the replies! Here is some of the
> information that
> was requested of me.
>
> We are using a cone 10 clay and all cone 10 glazes. Just about
> every one of
> our glazes are shivering--that is razor sharp pieces popping off on
> both lips of
> work and on flat planes of the work. All work is fired in reduction.
>
> Our clay body is:
>
> Hawthorn Fireclay- 33
> Gold Art- 25
> C and C Ball- 25
> Custer Feldspar- 7
> Silica- 7
> Fine Grog- 7
>
> (for the sculpture body also add Medium Grog-7)
>
> This is my second year at this institution and, from what I
> understand, this is
> a new issue. Both my sculpture and throwing studens are having
> issues.
>
> Some of the worst glazes are:
>
> Salt Yellow:
> Neph Sye- 60.7
> Dolomite- 20
> Zircopax- 15.2
> C & C Ball Clay- 4.1
> Bentonite- 3.8
> RIO- .9
>
>
> Celedon:
> Custer- 262
> Whiting- 52
> Zinc Oxide- 8
> Kaolin- 47
> Silica- 59
> RIO- 8
> Bentonite- 1.5
>
>
> As I said though, all of our glazes are shivering, which makes me
> think this is a
> claybody issue. Could it me the Custer? If so, what do I do to
> remedy this?
>
> Thank you all so much,
> Susannah
Susannah Biondo-Gemmell on tue 6 dec 11
Sorry for the confusion.=3D20=3D20
We are having major shivering issues with our iron yellow, and only some =
=3D
with=3D20
our salt yellow.
Troy's Iron Yellow
45 Custer
23 Flint
17 Whiting
13 Kaolin
2 Zinc Oxide
7 Iron Oxide
Again, there is quite a bit of Custer in this recipe. I am wondering if =
=3D
this is all=3D20
linked to issues with Custer Feldspar. Both our clay and many glazes hav=
=3D
e=3D20
Custer. Any ideas if this is the true culprite and, if so, how to fix th=
=3D
e clay=3D20=3D20
body.
Susannah
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