Toni Hall on mon 19 oct 98
Hi all,
I have developed a problem with my two white cone 6 glazes and I am seeking
an explanation. I have been using two different white, opaque glazes. One is
called 148 (unknown origin, but I got it from a class I took), and it is a tin
white. The other one is Tony Hansen's "All Purpose" 20 base cone 6 posted on
his digitalfire, and I use zircopax. Both of these have worked in the past,
and work from time to time, so I am sure I am doing something in error and I
don't realize it is causing the glaze to react this way. I am using both red
and white (B mix cone10) clay, and have dipped and brush on the glaze.
However, every so often a very smooth appearing application comes out of the
kiln with almost bare spots on the pot. It looks like pin holes, but can be
uneven, like it is peeling or rolling off of a spot like it had been waxed. If
it went on smooth and even, why didn't it fire out even? Can any of you help
me? Thank in advance, Toni
Cindy on tue 20 oct 98
Toni,
I'm not sure, but it sounds as if you may have some dirty bisque-ware. Dust
specks can cause pin-holing and grease (from oils on your fingers, maybe?)
can cause the sheeting you describe. Also, if your kiln fires very slowly,
the glaze can eventually run down, sometimes leaving unpredictable thin
spots. In addition, make certain your glazes are well-stirred. Different
minerals in your glaze can tend to settle to different levels in the bucket
and unless the glaze is mixed thoroughly, you may end up with problems such
as you describe.
Cindy Strnad
Earthen Vessels
Custer, SD
USA http://blackhills-info.com/a/cindys/menu.htm
----------
> From: Toni Hall
> To: CLAYART@LSV.UKY.EDU
> Subject: Pinholes and peeling
> Date: Monday, October 19, 1998 7:26 AM
>
> ----------------------------Original message----------------------------
> Hi all,
> I have developed a problem with my two white cone 6 glazes and I
am seeking
> an explanation. I have been using two different white, opaque glazes.
One is
> called 148 (unknown origin, but I got it from a class I took), and it is
a tin
> white. The other one is Tony Hansen's "All Purpose" 20 base cone 6 posted
on
> his digitalfire, and I use zircopax. Both of these have worked in the
past,
> and work from time to time, so I am sure I am doing something in error
and I
> don't realize it is causing the glaze to react this way. I am using both
red
> and white (B mix cone10) clay, and have dipped and brush on the glaze.
> However, every so often a very smooth appearing application comes out of
the
> kiln with almost bare spots on the pot. It looks like pin holes, but can
be
> uneven, like it is peeling or rolling off of a spot like it had been
waxed. If
> it went on smooth and even, why didn't it fire out even? Can any of you
help
> me? Thank in advance, Toni
>
Greg Lamont on wed 21 oct 98
At 09:26 AM 10/19/98 EDT, you wrote:
>----------------------------Original message----------------------------
>Hi all,
> I have developed a problem with my two white cone 6 glazes and I
am seeking
>an explanation. I have been using two different white, opaque glazes.
One is
>called 148 (unknown origin, but I got it from a class I took), and it is a
tin
>white. The other one is Tony Hansen's "All Purpose" 20 base cone 6 posted on
>his digitalfire, and I use zircopax. Both of these have worked in the past,
>and work from time to time, so I am sure I am doing something in error and I
>don't realize it is causing the glaze to react this way. I am using both red
>and white (B mix cone10) clay, and have dipped and brush on the glaze.
>However, every so often a very smooth appearing application comes out of the
>kiln with almost bare spots on the pot. It looks like pin holes, but can be
>uneven, like it is peeling or rolling off of a spot like it had been
waxed. If
>it went on smooth and even, why didn't it fire out even? Can any of you help
>me? Thank in advance, Toni
Hi Toni,
I'm sure others more knowledgeable than I will also respond to this, but it
sounds to me like a classic description of "crawling": one of the most
common glaze defects. There are many causes, but they seem to fall into
three categories: the glaze itself, application, and the bisqued pot. Some
possible causes? Glaze improperly formulated, glaze vsicosity too thick,
glaze application too thick, pot bisque fired too low. bisqued pot dusty or
greasy, pot glaze fired when glaze still damp, etc. Any good pottery book
(such as Hamer's Dictionary of Materials and Techniques; or Rhodes' Clay
and Glazes for the Potter) cover glaze faults in detail. As this problem
can be caused by any one or combination of thing, I suggest you read about
it first and see if you can asses the cause(s) yourself. Then, if you
still can't figure it out, I'm sure one of the lists wonderful glaze
experts can help you out.
Regards,
Greg Lamont
3011 Northwood Dr.
Ames, Iowa 50010-4750
515/233-3442
gdlamont@iastate.edu
Bacia Edelman on fri 23 oct 98
Toni: I glanced at Gred Lamont's post in today's Digest before trying to
answer. I am definitely NOT one of the list's glaze experts, far from it,
but something in your post makes me offer this for general consideration by
you and others.
You are using cone 6 glazes on a cone 10 B-mix. You know, Laguna sells a
B-mix 5, described as offering the same characteristics "enjoyed by our Cone
10 B-mix."
That clay will definitely fire to cone 6 and maybe cone 7.
My theory is that your clay body is not mature at cone 6, and that can cause
serious problems with glaze fit. As for the peeling, and Greg is right, you
may mean "crawling", follow his and other suggestions for how to handle the
bisque, and one of them was to bisque higher, I believe.
Check "pinholing" under Glaze Flaws in any of the books Greg mentioned, or I
think there is one out by a Frazer or Frazier. Check The Potters' Shop
flyer for its title.
May I add a personal note to the list's glaze gurus, who might also answer.
John Post and Ron Roy found a glaze I offered someone (David Hendley is
right: I probably will never offer a glaze on the list again until I work
with my just downloaded GlazeChem software, for which I have no time right
now) to be not FOODSAFE, though I took it from Lana Wilson's book that said
it WAS food safe. I wrote each of them my plight of needing to glaze, in a
hurry, a group of bowls I had thrown for the Empty Bowls Food for the Hungry
fundraiser. I mostly do non-functional pots or am a dysfunctional potter.!!
John sent me some excellent recipes and formulae, Ron converted Lana's
glaze, named Heino Render, which till then I had only used on vases etc.
Both glazes fine and as soon as I catch your e-mail address again, Ron, will
write you with the recipe you sent. I still need to adjust the color to
suit me.
Back to Toni: I hope you can solve your dilemma. Let us know.
Bacia Edelman Madison, Wisconsin
On Oct. 19, you wrote:
Hi all,
I have developed a problem with my two white cone 6 glazes and I am
seeking
an explanation. I have been using two different white, opaque glazes. One is
called 148 (unknown origin, but I got it from a class I took), and it is a tin
white. The other one is Tony Hansen's "All Purpose" 20 base cone 6 posted on
his digitalfire, and I use zircopax. Both of these have worked in the past,
and work from time to time, so I am sure I am doing something in error and I
don't realize it is causing the glaze to react this way. I am using both red
and white (B mix cone10) clay, and have dipped and brush on the glaze.
However, every so often a very smooth appearing application comes out of the
kiln with almost bare spots on the pot. It looks like pin holes, but can be
uneven, like it is peeling or rolling off of a spot like it had been waxed. If
it went on smooth and even, why didn't it fire out even? Can any of you help
me? Thank in advance, Toni
Toni Hall on mon 26 oct 98
Bacia Edelman wrote:
Bacia,
Thank you for your input on my pinholes and peeling problem. I would suspect
it were the clay, except I fire other glazes on this same body and they do
fine. I am convinced it is the speed of firing and maybe dirt on the pots.
But the problem is just with the white glazes, and it is not always a problem.
I am going to fire the next load much slower and I think that will fix it,
but thanks again for your suggestions. Toni
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