Marni Turkel on mon 19 jun 00
I'm hoping for some input on a problem I am having with a new glaze I have
been working on (with much help from Ron Roy on glaze chemistry). I really
like the surface and color, but I get some patches of wrinkles on the
surface, which neither Ron nor I could understand.
About a week ago, in the thread on firing bisque and glaze together Jeff
Lawrence wrote "My base 04 mat glaze contains zinc oxide and wrinkles up if
there is a lot of bisque in the same load. According to Parmalee (only one
who mentions this flaw), zinc reacts with sulfur-containing gases released
by the bisqueware."
This is a high zinc glaze, so maybe this is my problem.
I use a c5 casting slip (with some barium to deal with any impurities). I
bisque to a witness cone 05 with an Skutt Envirovent on for the whole
firing. The pieces are then glaze fired to a witness cone of cone 5
(electric) with a vent on through the entire firing. There is no wax on the
pieces. Since I installed vents about a year ago, I no longer vent with the
lid or top peephole open, I just turn on the vent and proceed, assuming
that this is enough to keep a clear atmosphere. Until this test glaze, I
haven't seen a problem. Has anyone found that this just isn't enough
ventilation?
Since the clay has already been bisqued, could there still be residual
sulfur left over in the clay from insufficient venting in the bisque firing?
Would I know if my glaze is contaminated with sulfur? At what temperature
does sulfur burn out? I use copper and manganese carbonates in one of my
glazes and it will leave a yellow fumed ring on the kiln wash on the shelf.
The same base with other colorants does not do this. I have always thought
this was sulfur contamination in the copper or manganese and that my other
glazes were clean. (I have learned over the years that many of my
assumptions and theories about clay have no basis in fact, this could be
just one more example of that.) Because of copper contamination, I have a
separate set of shelves, posts and kiln that I use for a light colored
glazes that would otherwise pick up copper fumes. The test glaze will get
wrinkled patches in a kiln that never had the green glaze just the same as
in a firing with a lot of the green.
Has anyone had wrinkled glazes from any other source?
I appreciate any suggestions. If I get the energy tomorrow, I'll ask the
list about a crawling problem I am having with another glaze I'm working
on. I am determined to have some new glazes, but it isn't easy.
Thank you,
Marni
Marni Turkel
Stony Point Ceramic Design
2080 Llano Rd 1B
Santa Rosa, CA 95407
Pottery: 707-579-5567
Office: 707-579-9511
Fax: 707-579-1116
Fredrick Paget on tue 20 jun 00
Marnie,
I once contaminated a small Skutt kiln with niobium fumes from an attempt
to make the oxide by firing some niobium netal. After that for three or
four firings I got wrinkled glazes on pots near the spot where the niobium
had been placed (Low down and in the back of the kiln.) It finally burned
out.
Your idea about sulfer is a good one. Why not design an experiment to test
it? The ware might be picking up sulfate from the molds which are plaster
made from gypsum - Calcium sulfate (CaSO4). It is very slightly soluble in
water (0.3 grams per 100 ml) and possibly the slip formula might exagerate
that solubility. CaSO4 does not break down (melts around 1450 C) on firing
though so what other form of sulfur compound could be in there?
Fred
>I'm hoping for some input on a problem I am having with a new glaze I have
>been working on (with much help from Ron Roy on glaze chemistry).
>.....Etc......
>From Fred Paget, Marin County, California, USA
Dave Murphy on tue 20 jun 00
Dear Marni:
I had wrinkles in a temoku glaze once (reduction, cone 10) and was told at
the time that it was devitrification of the glaze because the kiln cooled
very slowly. I have no idea if this was correct as it never happened again
so I did not pursue it.
Barbara Murphy
Waterloo, Ontrario
----- Original Message -----
From: Marni Turkel
To:
Sent: Tuesday, June 20, 2000 1:50 AM
Subject: Wrinkled glaze and kiln venting
> I'm hoping for some input on a problem I am having with a new glaze I have
> been working on (with much help from Ron Roy on glaze chemistry). I really
> like the surface and color, but I get some patches of wrinkles on the
> surface, which neither Ron nor I could understand.
>
> About a week ago, in the thread on firing bisque and glaze together Jeff
> Lawrence wrote "My base 04 mat glaze contains zinc oxide and wrinkles up
if
> there is a lot of bisque in the same load. According to Parmalee (only one
> who mentions this flaw), zinc reacts with sulfur-containing gases released
> by the bisqueware."
>
> This is a high zinc glaze, so maybe this is my problem.
>
> I use a c5 casting slip (with some barium to deal with any impurities). I
> bisque to a witness cone 05 with an Skutt Envirovent on for the whole
> firing. The pieces are then glaze fired to a witness cone of cone 5
> (electric) with a vent on through the entire firing. There is no wax on
the
> pieces. Since I installed vents about a year ago, I no longer vent with
the
> lid or top peephole open, I just turn on the vent and proceed, assuming
> that this is enough to keep a clear atmosphere. Until this test glaze, I
> haven't seen a problem. Has anyone found that this just isn't enough
> ventilation?
>
> Since the clay has already been bisqued, could there still be residual
> sulfur left over in the clay from insufficient venting in the bisque
firing?
>
> Would I know if my glaze is contaminated with sulfur? At what temperature
> does sulfur burn out? I use copper and manganese carbonates in one of my
> glazes and it will leave a yellow fumed ring on the kiln wash on the
shelf.
> The same base with other colorants does not do this. I have always thought
> this was sulfur contamination in the copper or manganese and that my other
> glazes were clean. (I have learned over the years that many of my
> assumptions and theories about clay have no basis in fact, this could be
> just one more example of that.) Because of copper contamination, I have a
> separate set of shelves, posts and kiln that I use for a light colored
> glazes that would otherwise pick up copper fumes. The test glaze will get
> wrinkled patches in a kiln that never had the green glaze just the same as
> in a firing with a lot of the green.
>
> Has anyone had wrinkled glazes from any other source?
>
> I appreciate any suggestions. If I get the energy tomorrow, I'll ask the
> list about a crawling problem I am having with another glaze I'm working
> on. I am determined to have some new glazes, but it isn't easy.
>
> Thank you,
> Marni
>
>
> Marni Turkel
> Stony Point Ceramic Design
> 2080 Llano Rd 1B
> Santa Rosa, CA 95407
>
> Pottery: 707-579-5567
> Office: 707-579-9511
> Fax: 707-579-1116
>
>
____________________________________________________________________________
__
> 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.
>
Dave Finkelnburg on wed 21 jun 00
Marni,
For what it's worth, my recollection of the instructions with my Bailey
kiln vent was to fire with the top peep open, to provide some sweep of air
through the kiln. If the kiln was leaky enough, that probably wouldn't be
necessary. The vent hole was supposed to be about opposite the peep, but
down low, so it does provide some through ventilation.
Hope you can solve the wrinkling problem!
Dave Finkelnburg
-----Original Message-----
From: Marni Turkel
To: CLAYART@LSV.CERAMICS.ORG
Date: Tuesday, June 20, 2000 5:08 AM
Subject: Wrinkled glaze and kiln venting
>I'm hoping for some input on a problem I am having with a new glaze I have
>been working on (with much help from Ron Roy on glaze chemistry). I really
>like the surface and color, but I get some patches of wrinkles on the
>surface, which neither Ron nor I could understand.
>
>About a week ago, in the thread on firing bisque and glaze together Jeff
>Lawrence wrote "My base 04 mat glaze contains zinc oxide and wrinkles up if
>there is a lot of bisque in the same load. According to Parmalee (only one
>who mentions this flaw), zinc reacts with sulfur-containing gases released
>by the bisqueware."
>
>This is a high zinc glaze, so maybe this is my problem.
>
>I use a c5 casting slip (with some barium to deal with any impurities). I
>bisque to a witness cone 05 with an Skutt Envirovent on for the whole
>firing. The pieces are then glaze fired to a witness cone of cone 5
>(electric) with a vent on through the entire firing. There is no wax on the
>pieces. Since I installed vents about a year ago, I no longer vent with the
>lid or top peephole open, I just turn on the vent and proceed, assuming
>that this is enough to keep a clear atmosphere. Until this test glaze, I
>haven't seen a problem. Has anyone found that this just isn't enough
>ventilation?
>
>Since the clay has already been bisqued, could there still be residual
>sulfur left over in the clay from insufficient venting in the bisque
firing?
>
>Would I know if my glaze is contaminated with sulfur? At what temperature
>does sulfur burn out? I use copper and manganese carbonates in one of my
>glazes and it will leave a yellow fumed ring on the kiln wash on the shelf.
>The same base with other colorants does not do this. I have always thought
>this was sulfur contamination in the copper or manganese and that my other
>glazes were clean. (I have learned over the years that many of my
>assumptions and theories about clay have no basis in fact, this could be
>just one more example of that.) Because of copper contamination, I have a
>separate set of shelves, posts and kiln that I use for a light colored
>glazes that would otherwise pick up copper fumes. The test glaze will get
>wrinkled patches in a kiln that never had the green glaze just the same as
>in a firing with a lot of the green.
>
>Has anyone had wrinkled glazes from any other source?
>
>I appreciate any suggestions. If I get the energy tomorrow, I'll ask the
>list about a crawling problem I am having with another glaze I'm working
>on. I am determined to have some new glazes, but it isn't easy.
>
>Thank you,
>Marni
>
>
>Marni Turkel
>Stony Point Ceramic Design
>2080 Llano Rd 1B
>Santa Rosa, CA 95407
>
>Pottery: 707-579-5567
>Office: 707-579-9511
>Fax: 707-579-1116
>
>___________________________________________________________________________
___
>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.
>
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