Dave Finkelnburg on mon 12 mar 01
Hi Dawn!
Sounds like you had a dismal experience with your glaze test. I'm
really sorry to hear that. :-( I've been there before myself, though not
with anything as bad as it sounds like you experienced.
I think there is an error in the glaze formula you posted. As posted,
the glaze will not work. The basis for this sort of glaze goes back a long
way, and most versions of this contain 15% or so kaolin rather than talc.
If you make that substitution you will have a glaze that will work -- but
read the qualifications below.
This glaze will still be very high in boron, which may make it unstable.
By that I mean it may leach out harmful chemicals. Before using it on any
food surface, as a responsible potter you should have it tested to make sure
it will not leach dangerous amounts of boron or any heavy metal colorant
oxides (copper, chrome, cobalt, nickel, tin, etc).
Also, while high boron glazes can yield some wonderfully interesting
surfaces, you do get into glaze fit issues and application problems,
challenges which can be avoided by using glaze recipes which fall more
closely within "limits." If you want to use this glaze, and I am not
suggesting you shouldn't, just be aware that is has some shortcomings you
will have to put up with.
By the way, when testing new glaze recipes from someone else, it may be
prudent to first fire a single test tile by putting it on a flat "pancake"
or shallow bowl of clay so if you have a runny glaze, it winds up on the
pancake, not your shelf. You can keep reusing the pancake as long as you
don't hit a runny glaze. It's cheap insurance and saves a lot of chipping!
Good testing!
Dave Finkelnburg
Idaho Fire Pottery
C TRIPP on mon 12 mar 01
Hi Dawn,
As a newish glaze maker I would second the motion that John H. gave you; go
to Tony Hansen's site and study his 5x20. Then after you are more educated
and experienced, branch out to the exotica. (Or do the basics and one exotic
at a time, just for fun.)
I would hazard a guess that the Colemanite played a major part in your
'vomit.' I bought some bits and pieces from a retired potter; including
Colemanite. I read up on it in the Clayart archives (the one where you type
in the topic and everywhere that word is mentioned, you get a listing) and
found that some Colemanite has gypsum in it and causes spitting. Well, the
ex-potter is from Oz, we both live in the Middle East, she bought stuff from
NZ, Oz, and the UK so who knows where this Colemanite was from. So, I
tested it on a small cup placed inside a gash bowl. It spit. Lovely glaze
though...
Good luck with future glazing. (You will find that some glazes don't vomit,
they just look that way.)
Carol
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Daraburn@AOL.COM on mon 12 mar 01
I'm trying to teach myself glazing...What an adventure! I mixed up Floating
Red that I got off this list. Fired to cone 6. What a disaster! It was
more like "vomiting" than spitting! All the glaze was spattered all around
the cup and all that was left on the cup was a thin stained uneven metalic
look...very ugly. On the inside of the cup the pool at the bottom was sorta
red but with "scabs". How do you like my descriptions? What happened? I
really hate ruining my shelves like that!...not to mention my ego.
Here's the recipe that I used on white stoneware:
Colemanite 55
Talc 15
Flint 30
Red Iron Oxide 22
Thanks,
Dawn
John Hesselberth on mon 12 mar 01
Daraburn@aol.com wrote:
>I'm trying to teach myself glazing...What an adventure! I mixed up Floating
>Red that I got off this list. Fired to cone 6. What a disaster! It was
>more like "vomiting" than spitting! All the glaze was spattered all around
>the cup and all that was left on the cup was a thin stained uneven metalic
>look...very ugly. On the inside of the cup the pool at the bottom was sorta
>red but with "scabs". How do you like my descriptions? What happened? I
>really hate ruining my shelves like that!...not to mention my ego.
>Here's the recipe that I used on white stoneware:
> Colemanite 55
> Talc 15
> Flint 30
> Red Iron Oxide 22
>
>Thanks,
>Dawn
Hi Dawn,
Welcome to the wonderful word of glaze formulation. Unfortunately, I
think you picked an initial recipe to try that is a disaster waiting to
happen. It has almost no alumina which means it will probably run right
off the pot. It has a very low level of silica which means it will be
very unstable or non-durable. Also it has a very high level of boron
which means it well be VERY well melted at cone 6. I don't have a clue
why anyone would have posted a glaze like this unless they were proposing
it for a macrocrystalline glaze. Some macrocrystalline glazes have a
formula similar to this--those kind of glazes are best left until you
have a lot of experience with glazes.
So, in short try another starting point for your exploration of glazes.
Tony Hansen's 5/20s would be a good glaze to start with. Then when you
have mastered it or one similar to it, branch out to more "interesting"
formulations.
Regards, John
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Yvon LeDouget on mon 12 mar 01
Bonjour
Do you know colemanite formula ?
2 CaO 3 B2O3 5 H2O
5 H2O...It is just the problem !
You can try to calcine your glaze before or to bring B2O3 in your glaze with
a fritt.
Yvon
Joyce Lee on wed 14 mar 01
> No Joyce! this time you are wrong!
I realized THAT just after hitting the SEND button, Ababi. The thought
popped into my head too late that a) the fact that I've never achieved a
satisfying glaze with more than 15% RIO doesn't reflect the truth of
everybody else's experience .... and.... 2) my occasionally moving
decimals around when copying glaze recipes isn't indicative of all
clayarters copying abilities. What have we been saying lately? Shoulda'
thought before typing, and again before posting.
Thanks for the correction.
Joyce
In the Mojave where she found a tiny, tiny lizard in a shallow tenmoku
bowl of rainwater ... our critters are not accustomed to such
largess from the skies ... poor little guy could barely keep his head
above water and kept slipping&sliding trying to get out. How grand to be
the one to rescue him! He just lay there on the sand for a full ten
minutes before skittering away.
Nancy Guido on sun 18 nov 01
I was curious about this Alisa's Desert Wash (50-50 Borax and Ultrox,
4%rutile and 8% yellow ocher) so I mixed up a batch. I didn't have Ultrox so
I used Superpax and tried it out on Tucker's Midcal 5 - great glaze but it
did spit all over the kiln shelf. I still like it - a lot!
The other glazes I tested - whilst I was in the mixing mood - were Golden
Fake Ash, Frosty White, Ron Roy's Black #3, Pinnell's Weathered Bronze(and
the other variations - Periwinkle, Cream Tan, and White) and Conrad's Black
Engobe underneath Bell Lichen - that was fun! I didn't get the pinholes on
the Weathered Bronze, but the glaze samples were pretty thin. These were all
done on the Tucker's Midcal 5 - which is a toasty tan clay. The Golden Fake
Ash was just as described - with green streaks.
The Frosty white was nice but had little black specks? This was done on
white clay.
Frosty White Crystal ^5 (but it will go to ^8)
Neph Sye 42
Whiting 10
Zinc Oxide 18
Silica 30
Bentonite 3%
Golden Fake Ash, ^6
===================
REDART.............. 29.00 28.71%
OM #4 BALL CLAY..... 21.00 20.79%
BONE ASH............ 5.00 4.95%
STRONTIUM CARBONATE. 9.00 8.91%
DOLOMITE............ 25.00 24.75%
GERSTLEY BORATE..... 10.00 9.90%
LITHIUM CARBONATE... 2.00 1.98%
===
Thanks for the recipes!
Nancy G.
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