Oliver Hughes on wed 25 sep 02
I=92m looking for a recipe or formula for a cone 10 clear glaze that
has minimal or no crazing and works well over underglazes like
Duncan or Mayco. If you can help, it would be much appreciated.
Margaret H.
Dave Finkelnburg on wed 25 sep 02
Margaret and all,
I too am on a quest for a cone 10 clear for use over underglazes.
Besides working with underglazes and not crazing, my particular criteria is
for a truly clear glaze, as in no little entrained bubbles. I have had a
challenge finding a clear that doesn't entrain bubbles yet stays put and
doesn't flow on vertical surfaces. I'm willing to test. Anyone have
suggestions on what ingredients to start with to get that magic combination
of low viscosity and clarity in a cone 10 glaze?
Crazing, by the way, is a matter between your particular clay and the
glaze. Nobody can give you a recipe that won't craze on your clay unless
they know exactly what your clay body is. Even then you may have to do some
testing because clay bodies can vary from batch to batch. You must match
the expansion of the clay body and glaze to prevent crazing.
Dave Finkelnburg, firing a kiln load of test pots in Idaho
----- Original Message -----
From: "Oliver Hughes"
I'm looking for a recipe or formula for a cone 10 clear glaze that
has minimal or no crazing and works well over underglazes like
Duncan or Mayco. If you can help, it would be much appreciated.
Margaret H.
vince pitelka on wed 25 sep 02
Margaret, Dave, and others -
This is one I have tinkered with over the years, and it works great over
homemade slips, so I imagine it would work great over underglazes. Try it
and let me know. It crazes little, but I don't know what it will do on your
claybody.
Vince's Clear
G-200 Feldspar 22.0
OM-4 15.0
Neph. Sye 13.1
Flint 13.0
Cornwall Stone 12.8
Whiting 9.5
EPK 5.7
Talc 5.3
Barium Carb. 3.6
Total 100.0
+ Bentonite 3%
artimater on wed 25 sep 02
Dave,
How about salt or soda?
PAX,
Rush
"I only indulge when I've seen a snake, so I keep a supply of =
indulgences and snakes handy"
http://artimator.com
rush@artimator.com
http://groups.yahoo.com/group/texasceramics/
Artimator Galleries
2420 Briarwood Ln.
Carrollton, TX 75006
972-841-1857
Ron Roy on sun 29 sep 02
>This is one I have tinkered with over the years, and it works great over
>homemade slips, so I imagine it would work great over underglazes. Try it
>and let me know. It crazes little, but I don't know what it will do on your
>claybody.
>Vince's Clear
>G-200 Feldspar 22.0
>OM-4 15.0
>Neph. Sye 13.1
>Flint 13.0
>Cornwall Stone 12.8
>Whiting 9.5
>EPK 5.7
>Talc 5.3
>Barium Carb. 3.6
>Total 100.0
>+ Bentonite 3%
This is probably the result of combining two other glazes - which would
explain the extended list of materials needed.
It has a ratio of 6.3 (6.3 mols of for every one of alumina) This is
unusual for a clear glaze - most clears have a much higher ratio - closer
to 10 for instance. The high alumina - it's way over the limits for cone 10
glazes - maybe responsible for it's lack of bubbles and I am wondering if
it's durability in compromised as well because of the high alumina. It
would be interesting to see a test sample with 5% copper carb leach tested.
This would be important if stains were to be used under it.
I have reformulated it taking out three problematic materials - Neph Sy,
Cornwall Stone and Barium and added Strontium. When you replace Barium with
Strontium you need less Strontium - because they have similar COE's you
thereby get and advantage when dealing with crazing.
I am interested in the bubble thing so I have done another glaze - taking
out more alumina and increasing the silica to alumina ratio- and lowering
the expansion so it will not craze on most porcelains. If anyone is
interested in doing the experiments I would be grateful if they would post
the results.
RR revision #1
G200 - 42.0 (Custer will work fine)
Whiting - 10.0
Talc - 6.0
Strontium carb. - 3.0
OM#4 - 16.0
EPK - 7.0
Silica - 16.0
Bentonite - 2.0 Probably not be needed without the Neph Sy)
Total -- 102.0
RR revision #2 (lower alumina and silica up - expansion lowered to avoid
crazing even on porcelains. Strontium replaced Calcium using wollastonite -
whiting out - CaO replaced with wollastonite.
G200 - 38.0 (Custer will work fine)
Wollas - 17.0
Talc - 3.0
OM#4 - 13.0
EPK - 5.0
Silica - 24.0
Bentonite - 2.0 (Probably not be needed without the Neph Sy)
Total -- 102.0
Revision #3 is equal amounts - by volume of #1 + #2
Note - expansion is low enough that it could shiver on or break some ware
made from high expansion clay bodies containing cristobalite generated
during firing - test for fit on all stoneware bodies. Test for fit on all
slips is always a good idea.
Testing glazes on slips with soon give you information on how those slips
fit with your clay bodies. It is one thing to get glazes working well on
your clays but when you introduce a third layer you should be aware - it
complicates the fit problem. It is why making your slip out of your clay
body is a sensible thing to do if you can.
RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
John Stromnes on mon 30 sep 02
Margaret, Dave, Vince, Hank, Ron, Etc:
I have tried several 'clear' glazes since I've been firing gas COne 10 in
the kiln I built. They all more or less craze on my three clay bodies. I
have tried adding silica in 2.5, 5 percent, 10 percent increments, and it
hasn't helped. Does anybody have a non-technical, relatively painless way
to adjust these sensitive clears to prevent crazing? My clears seem
especially prone to crazing on the inside surfaces of curved forms, e.g.
bowls, and don't always craze oh the ou;side surface. Is that a function
of glaze thickness or clay body expansino? I fire to cone 9-10, depending
on the weather, and use whit/buff e bodies with about 11-12 percent
shrinkage, a little sand in one of them, and no grog. Could I add sand or
grog to the clay body to decrease shrinkage? Or would that make things
worse. If I add an opacifier or more clay to these same clears, the crazing
seems to cure itself. Or maybe I just I can't see it? Anybody else out
there with this nagging problem?
John Syodo Stromnes
Gary Elfring on thu 3 oct 02
Hello John,
Monday, September 30, 2002, 6:19:00 PM, you wrote:
JS> Margaret, Dave, Vince, Hank, Ron, Etc:
JS> I have tried several 'clear' glazes since I've been firing gas COne 10 in
JS> the kiln I built. They all more or less craze on my three clay bodies. I
JS> have tried adding silica in 2.5, 5 percent, 10 percent increments, and it
JS> hasn't helped. Does anybody have a non-technical, relatively painless way
JS> to adjust these sensitive clears to prevent crazing? My clears seem
JS> especially prone to crazing on the inside surfaces of curved forms, e.g.
JS> bowls, and don't always craze oh the ou;side surface. Is that a function
JS> of glaze thickness or clay body expansino? I fire to cone 9-10, depending
JS> on the weather, and use whit/buff e bodies with about 11-12 percent
JS> shrinkage, a little sand in one of them, and no grog. Could I add sand or
JS> grog to the clay body to decrease shrinkage? Or would that make things
JS> worse. If I add an opacifier or more clay to these same clears, the crazing
JS> seems to cure itself. Or maybe I just I can't see it? Anybody else out
JS> there with this nagging problem?
The easiest way I know to solve this problem is to follow Ian Currie's
grid test method. His book, "Revealing Glazes" explains it. You
basically take your glaze and make 35 variations of it, each one
differing in some small way from the next. A single test tile, (it's
big) with all 35 variations will give you the recipe to eliminate the
crazing.
It takes about 3 hours to mix the glaze variations and make a test
sheet, but it is well worth it.
I have the opposite problem- I develop my own cone 10 celadon glazes
and *want* crazing. I have done a number of test runs using Ian
Cirries method on my different clay bodies. I keep two
recipies- 1 that crazes just the way I want, and 1 with no crazing for
more functional work.
You can usually find an Ian Currie workshop somewhere near you each
year. That's how I learned. (It's a lot easier than just reading the
book and trying it yourself.)
--
Best regards,
Gary mailto:info@elfring.com
Betty Fountain on thu 3 oct 02
Hi John,
In reference to your crazing problem:
A couple of weeks ago, I had the opportunity to speak with Tom Coleman. I
was asking him about his "Ice Blue Celedon" glaze formula which was in the
June/July/August 2002 issue of Ceramics Monthly. It is an "almost clear"
glaze. He stated that if it crazes, which it has a tendency to do, to
substitue 1/2 or all of the silica with Imsil-A25. This is available thru
mail-order from Aardvark Supplies in Orange Co., Calif. (Phone #:
714-541-4157).
Hope this helps.
Regards,
Betty Fountain
Stonington, Connecticut
Des & Jan Howard on fri 4 oct 02
Could someone please tell me what "Imsil-A25" is?
Des
Betty Fountain wrote (in part):
> He stated that if it crazes, which it has a tendency to do, to
> substitue 1/2 or all of the silica with Imsil-A25. --
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
June Perry on fri 4 oct 02
Charles, it depends on the glaze. If you're getting only a hair of crazing,
maybe replacing half the silica would work. You'll pay more for it than your
regular 200-400 mesh silica, and more if you're having to have it shipped.
Because of the fineness of it, it may also cause earlier melt, so you just
may want to test it a bit before making a large batch.
I haven't purchased any since I've been here in Florida. Someone mentioned
that Aardvark in California has it; but there are probably other sources as
well. If you have a local supplier, and are willing to buy a bag of it, he
could probably get it for you in his next material shipment.
Warm regards,
June
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