Susan Davy on sun 17 aug 97
atten: Glaze Chemists...I have been testing a cone 9-10 matt blue glaze
with initial great results. After deciding to add this glaze to my
production line, it has been failing big time. The formula is:
custer spar--1020
whiting------ 180
zinc ox------ 160
barium carb-- 400
ball clay OM#4-200
rutile-------- 40
copper ox----- 10
cobalt ox----- 10
I have fired in total reduction from cone 08 on up to finish. And have
tried a body reduction, back to oxidation, and a 45 min. glaze reduction
at cone 9. The glaze is covered in some areas with little
bubbles...other areas are beautifully smooth. These bubbles do not
refire out. Does anyone know why this is happening?
thanks in advance..
Susan Davy pottery@minot.com
Rick Sherman on mon 18 aug 97
-------------original message----------------
....I have been testing a cone 9-10 matt blue glaze with initial great
results. After deciding to add this glaze to my production line, it
has been failing big time. The formula is:
custer spar--1020
whiting------ 180
zinc ox------ 160
barium carb-- 400
ball clay OM#4-200
rutile-------- 40
copper ox----- 10
cobalt ox----- 10
I have fired in total reduction from cone 08 on up to finish. And
have tried a body reduction, back to oxidation, and a 45 min. glaze
reduction at cone 9. The glaze is covered in some areas with little
bubbles...other areas are beautifully smooth. These bubbles do not
refire out. Does anyone know why this is happening?
Susan Davy
------------------------------reply----------------------------------
I think it may be the rutile that is acting up. I have found it loves
to boil in a reducing atmosphere when applied to white stoneware or
porcelain. Have not had as bad experience with the more open red
stonewares. Perhaps you don't need to reduce as much or can end the
firing with a short period of oxidation. I am certain some of our
glaze experts will have some good ideas.
RS
Ron Roy on mon 18 aug 97
My guess, without knowing your bisque firing cycle, is it's the Zinc which
is easily reduced and there is a lot - 8%. When Zinc is reduced to the pure
metal it boils at even low temperatures -
Could also be the Rutil - some others have had some problems with it.
This glaze is seriously short of silica by the way and there is a lot of
Barium present - there are those of us who would never use this glaze where
it could come in contact with food.
>----------------------------Original message----------------------------
>atten: Glaze Chemists...I have been testing a cone 9-10 matt blue glaze
>with initial great results. After deciding to add this glaze to my
>production line, it has been failing big time. The formula is:
>custer spar--1020
>whiting------ 180
>zinc ox------ 160
>barium carb-- 400
>ball clay OM#4-200
>rutile-------- 40
>copper ox----- 10
>cobalt ox----- 10
>
>I have fired in total reduction from cone 08 on up to finish. And have
>tried a body reduction, back to oxidation, and a 45 min. glaze reduction
>at cone 9. The glaze is covered in some areas with little
>bubbles...other areas are beautifully smooth. These bubbles do not
>refire out. Does anyone know why this is happening?
>
>thanks in advance..
>Susan Davy pottery@minot.com
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
rballou@mnsinc.com on mon 18 aug 97
I think the more likely culprit is the zinc rather than the rutile, though
you never know, it could be both! There are a lot of reduction glaze
recipes that call for zinc. I used to mix up two samples when testing one
of these glazes, one with zinc and one without, no other change. The two
fired samples esentially showed the same glaze, except that the ones
without zinc didn't have any flaws. And sometimes the small sample tiles
with zinc wouldn't show any problems, either. But sooner or later, larger
samples of the glaze with zinc exhibited all kinds of problems: pitting,
crawling, blistering, hard bumps under the surface of the glaze.If this
weren't bad enough, zinc volatilizes during the firing and then condenses
into a poisonous dust in the atmosphere. This information and more can be
found in The Potter's Dictionary by the Hamers.
Now, I just omit the zinc if it's in a reduction recipe. I figure since the
zinc is burning out early in the firing, it's not contributing anything to
the glaze anyway. So far, I haven't come across a glaze that's needed any
adjustment to compensate for the absence of the zinc.
Ruth Ballou
rballou@mnsinc.com
>----------------------------Original message----------------------------
>My guess, without knowing your bisque firing cycle, is it's the Zinc which
>is easily reduced and there is a lot - 8%. When Zinc is reduced to the pure
>metal it boils at even low temperatures -
>
>
>Could also be the Rutil - some others have had some problems with it.
May Luk on sun 13 mar 11
Lily;
The Ceramic Review glaze book is even less useful now that I live in
the US. It is nothing but a glaze recipe porn. I'm glad that you found
it useful.
The Knowledge / Grounding written by Michael Bailey in Ceramic Review
now is very good though. He teaches us how to think.
In earlier times, possibly before there were remote control for TV, or
before Randy was red, potters just mixed a primary flux, a secondary
flux, some clay and some silica and find the melting point of a glaze
by line-blending. Then opacifier or colorants are added to achieve the
appearance they want.
What I just described is the best way to learn about glaze and no
maths or hard science involved if that's not how one rolls. It takes
a couple of hours a week and in a month, one can learn a lot. But that
would be too systemic and too efficient, wouldn't it? Most of us like
a look book before a how-to.
My mother used to hide my brother and my books near exam times, cause
we read so much, we wouldn't do our homework or study. I still read
too much.
Best Regards
May
Brooklyn NY
>
> May Luk =3DA0informs us she just hates one of my favorite books:"Clays an=
d
> Glazes: The Ceramic Review Book of Clay Bodies and Glaze Recipes " =3DA0I=
=3D
=3DA0am
> sorry. =3DA0Which brings this to mind. =3DA0My mother never censored what=
I
> could/could not read.
> This all was in earlier times, when every intimate detail of human life
> was not posted relentlessly on =3DA0TV and the Internet, so the young
> still had some naivete. Once, and only once, did Mother say, no,
> "I do not want you to read this. =3DA0Wait till you are older." =3DA0Mama=
n ra=3D
rely
> was right, but there she was. =3DA0Had May and Co. waited =3DA0a little l=
onge=3D
r,
> till they had read a few basic clay books...she probably would like CRBCB=
=3D
GR,
>
>
>
>
> Having said this, what =3DA0I was talking about was a glaze that someone =
ha=3D
s
> seen/used in recent times. =3DA0 In SO many cases a glaze used in a Commu=
ni=3D
ty
> Center, or college class, or at the Y or like that. =3DA0And the student =
go=3D
es
> home and tries it and Mitzy's Glorious White, turns grey or tan, or devel=
=3D
ops
> defects previously not seen. And student thinks, "Oh my goodness, what ha=
=3D
ve
> I done?" =3DA0not thinking that the only thing done was that s/he is usin=
g =3D
a
> different clay body.
>
>
> Lili Krakowski
> Be of good courage
>
--=3D20
http://twitter.com/MayLuk
http://www.takemehomeware.com/
Lili Krakowski on sun 13 mar 11
Paul:
You write : "Other than the statement that the clay body is the biggest
factor in glaze success your post is right on in my opinion. It is
definitely the most overlooked by beginners but I would suggest that in
trying a published glaze the biggest cause of failure is the firing
procedure. Many published glazes, in electric, are published with a cone
designation that appears to refer more to what cone was in the sitter ( old
tech) rather than the actual cone firing temp. Rate of rise, holding temp
etc. can make huge differences in the glaze appearance. "
No comment, no changed mind. Published glazes are a
happy free-for-all, many going back decades. Behrens, of blessed
memory, published his "Ceramic Glazemaking" in 1967 and "his"
Potash Feldspar probably no longer exists. And, my generation broke
its collective heart trying Leach glazes published without Seger formulas.
nor analysis of materials.
I--among others--have pointed out ad nauseum, that materials
-- Colemanite, Gertsley Borate , and many feldspars and clays--have
disappeared from the market, there are countless glazes
with different recipes and almost identical formulas. So when one
uses a published glaze one really is taking a fun shot in the dark.
May Luk informs us she just hates one of my favorite books:"Clays and
Glazes: The Ceramic Review Book of Clay Bodies and Glaze Recipes " I am
sorry. Which brings this to mind. My mother never censored what I
could/could not read.
This all was in earlier times, when every intimate detail of human life
was not posted relentlessly on TV and the Internet, so the young
still had some naivete. Once, and only once, did Mother say, no,
"I do not want you to read this. Wait till you are older." Maman rarely
was right, but there she was. Had May and Co. waited a little longer,
till they had read a few basic clay books...she probably would like CRBCBGR=
,
Having said this, what I was talking about was a glaze that someone has
seen/used in recent times. In SO many cases a glaze used in a Community
Center, or college class, or at the Y or like that. And the student goes
home and tries it and Mitzy's Glorious White, turns grey or tan, or develop=
s
defects previously not seen. And student thinks, "Oh my goodness, what have
I done?" not thinking that the only thing done was that s/he is using a
different clay body.
As to "new tech". Oy! Ouch! I have no doubt digital kilns are worth
their weight in gold. After all they they cost their weight in gold! But
many of us dear old things --graciously, charmingly, referred to by a
fellow ClayArter as "dinosaurs"-- keep the kilns we have had for years, an=
d
fire by the
cycles and rates we always have, and see no reason to
change . Nor can many of us afford to.
Furthermore: changing and adjusting firing cycles, cooling and like that,
is
a pretty "obvious" adjustment. I expect--do not know--that when a
particular glaze demands a particular firing cycle that info is handed out
along with the recipe. But what rarely is publishes/passed on is what body
the glaze was finalized on.
People are not warned about that, told about that, and weep bitter tears
because of it.
Lili Krakowski
Be of good courage
Steve Slatin on mon 14 mar 11
Lili -- in general I am in sympathy with the lament,
but electronic scales no longer cost their weight in
gold -- rather like electronics generally, they have
had a plummet it costs, and good scales are available
widely for prices far below those of the old reliable
metal triple-beam balance scales.
Steve Slatin --=3D20
--- On Sun, 3/13/11, Lili Krakowski wrote:
.
>=3D20
> As to "new tech".=3DA0 Oy!=3DA0 Ouch! I have no
> doubt=3DA0=3DA0=3DA0digital kilns are worth
> their weight in gold.=3DA0 After all they=3DA0 they
> cost=3DA0 their weight in gold! But
> many of us dear old things --graciously, charmingly,
> referred to by a
> fellow ClayArter as "dinosaurs"-- keep the kilns we have
> had for=3DA0 years, and
> fire by the
> cycles and rates we always have, and=3DA0 see no=3DA0
> reason to
> change .=3DA0 Nor can many of us afford to.
> =3D0A=3D0A=3D0A
| |
|
