Sheilah Bliss on thu 23 jul 98
OK Glaze Officanados... here's another one for you to figure out. In Richard
Behrens' book GLAZE PROJECTS on pg. 44, there is a ^6 ox. glaze recipe: Glaze
With Markings. When I first used it, it was a nicely patterned glaze and took
different coloring oxides well. Now I can't seem to get it to look like
anything other than yesterdays oatmeal. In fact, the raw glaze won't even
stay on the bisqueware. It takes a while to dry, but when it does it cracks
and falls off anyway! It changed before my ingredients were used up and
replaced with new glaze ingredients. I've tried adding CMC, Epsom Salts,
bentonite, increasing Si, decreasing Si, using calcined kaolin, decreasing
Zinc or Titanium, increasing Zinc or Titanium.... I've bisqued from ^08 to
^04, used Seattle Pottery Supply's Alpine White and Vashon White clay bodies
and ClayArt Center's Idaho white. No luck. Any takers?
GLAZE WITH MARKINGS
Zinc Oxide 22.9
Whiting 4.6
Lithium Carbonate 5.5
China Clay 20.4
Cryolite 5.5
Flint 32.0
Titanium Dioxide 9.1
Sheilah in Spokane
BlissPots@aol.com
Mike Gordon on thu 23 jul 98
Hi,
Have you tried boiling water and mixing the zinc into it, cooling then
adding the other ingredients with water as usual, then add the zinc?Mike
Kris Bliss on fri 24 jul 98
>OK Glaze Officanados... here's another one for you to figure out. In Richard
In fact, the raw glaze won't even
>stay on the bisqueware. It takes a while to dry, but when it does it cracks
>and falls off anyway!
>Sheilah in Spokane
>BlissPots@aol.com
>
Sheilah, I'm not much of a qlaze chemist,,,but, i wonder
are you applying this too thick?? Do you dunk your pots
to clean the dust off??
just wondering, Kris
in anchorage,,still waiting for summer
kbliss@customcpu.com
Anchorage, Alaska
Sheilah Bliss on fri 24 jul 98
to clean the dust off??
just wondering, Kris>
Well Hello Kris!
That Neurotic glaze.... I've tried dunking bisque in thick (melted ice cream),
moderate (cream), thin (skim milk); I've tried brushing with big Haike
brushes. I usually clean any dust from bisque with water-moistened old cotton
sport socks or old terry towels pieces - rinsed after each wipe, rung out
pretty good. I use filtered water.
Although, none of my other glazes fall off while drying (that is just SO
weird!) I thought maybe I was forgetting to omit fabric softener when washing
the socks & towels, that traces of the softener might be causing this, so
washed them deliberately with soap only, and rinsed 'em heartily before wiping
the pot down.
Also, outright faucet-washed several bisque pieces for their 2nd try with this
glaze, let dry for a day or 2, popped 'em in the oven at 350F and let them
cook for several hours.... someone told me it's possible to cook residual
grease and organic dust from the surface this way. While bisque was still
warm, dunked the pieces in 12 hour old glaze (about "4% milk" thick). Got a
nice even not-too-thick layer. At first I had hope... but as 5 minutes
lumbered on by, the cracks started, the edges of the glaze cracks began
curling up, and after about 15 minutes some were falling off, but the glaze
still wasn't totally dry <--insert Twighlight Zone Theme here....
What I usually do after this ordeal is remove all this weird glaze stuff from
the piece, wash off residuals, let it dry out again, re glaze it with a
different although inevitably more boring glaze, where the piece fires right
up just fine.
I've used several different clay bodies and - occasionally - the glaze has
worked on each.
Is there, by chance, a better way to remove the dust than I'm doing? I'm open
to anything.....
Humbly Hoping in High-Heat Spokane,
Sheilah Bliss
BlissPots@aol.com
Bob&Hulda on sat 25 jul 98
Dear Sheila,
I have not read your original message re.this
glaze,therefore do not know which ingredients you used.Could it be that the
formulation of your glaze is suitable only for greenware?What is the clay
content -kaolin,ball clay,bentonite-if any?Changing ball clay for Kaolin or
even better calcined kaolin may help.As I say I am only guessing,but if you
state the materials you use I would have a clearer picture of what is
happening.
Bob Hollis
Ron Roy on sat 25 jul 98
Hi Sheilah,
When I look at the molecular formula of this glaze I see it is out of
balance for even a cone 04 glaze. At cone 6 it is short of silica and way
over-supplied with ZnO. This makes it unfit for use on functional ware
where it can come in contact with food. There will be release of lithium
into food under some circumstances.
The Zinc oxide is probably the reason for the application difficulties - it
will shrink a lot as the glaze dries out - you may need to calcine your
zinc before weighing.
Lithium carbonate is problematic in glazes because some goes into solution
as salt - deflocculates the glaze slop and can crystallize out in the
bucket. I don't recommend the use of lithium carb in glazes unless there is
a good reason to have it there. If lithium oxide is really needed I
recommend using spodumene or petalite whenever possible.
Cryolite is also a problematic material as well - it is Sodium aluminum
fluoride. Its the fluoride coming out of the glaze during firing that can
be a problem producing bubbles and blisters. Cryolite is not often used in
glazes.
After all that I still don't know why the glazed changed - perhaps some
lithium has crystallized out of the slop - maybe the zinc oxide became so
dehydrated that it is causing the glaze to fall off during drying.
Perhaps a reformulation replacing some of the less than cooperative
materials would be worth a try.
As an after thought - have you changed your firing or cooling rate since it
worked the way you like it?
RR
> In Richard
>Behrens' book GLAZE PROJECTS on pg. 44, there is a ^6 ox. glaze recipe: Glaze
>With Markings. When I first used it, it was a nicely patterned glaze and took
>different coloring oxides well. Now I can't seem to get it to look like
>anything other than yesterdays oatmeal. In fact, the raw glaze won't even
>stay on the bisqueware. It takes a while to dry, but when it does it cracks
>and falls off anyway!
>GLAZE WITH MARKINGS
>Zinc Oxide 22.9
>Whiting 4.6
>Lithium Carbonate 5.5
>China Clay 20.4
>Cryolite 5.5
>Flint 32.0
>Titanium Dioxide 9.1
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Ruby Finkner on sat 25 jul 98
In a message dated 7/25/98 3:46:13 PM Eastern Daylight Time, ronroy@TOTAL.NET
writes:
<<
Lithium carbonate is problematic in glazes because some goes into solution
as salt - deflocculates the glaze slop and can crystallize out in the
bucket. I don't recommend the use of lithium carb in glazes unless there is
a good reason to have it there. If lithium oxide is really needed I
recommend using spodumene or petalite whenever possible.
Cryolite is also a problematic material as well - it is Sodium aluminum
fluoride. Its the fluoride coming out of the glaze during firing that can
be a problem producing bubbles and blisters. Cryolite is not often used in
glazes.
After all that I still don't know why the glazed changed - perhaps some
lithium has crystallized out of the slop - maybe the zinc oxide became so
dehydrated that it is causing the glaze to fall off during drying.
Perhaps a reformulation replacing some of the less than cooperative
materials would be worth a try.
As an after thought - have you changed your firing or cooling rate since it
worked the way you like it?
RR
> In Richard
>Behrens' book GLAZE PROJECTS on pg. 44, there is a ^6 ox. glaze recipe:
Glaze
>With Markings. When I first used it, it was a nicely patterned glaze and
took
>different coloring oxides well. Now I can't seem to get it to look like
>anything other than yesterdays oatmeal. In fact, the raw glaze won't even
>stay on the bisqueware. It takes a while to dry, but when it does it cracks
>and falls off anyway!
>GLAZE WITH MARKINGS
>Zinc Oxide 22.9 >>
Funny thing. I was having the same problem. A glaze that had always been so
well behaved suddenly cracked off of the bisque. I washed it off and tried
again. Same thing then I remembered that a friend had told me to use
wallpaper paste for something. So I tried it for this. Bingo no more
trouble. I think any wallpaper paste would do. I used Golden Harvest
cellulose wallpaper adhesive. Just put in a few sprinkles. It would be any
ones guess as to how much to use on a batch. I probably will try about a
teaspoon for two quarts. I had only about two cups left when I put in the
sprinkles. My glaze: Flint 55 EPK 25 Neph Sy 150 Whiting
60 Zinc 10. This is a nice buttery white. It makes a lovely brown
with iron. Hope this helps. Ruby
Sheilah Bliss on sun 26 jul 98
Hello Ron -
Geez! Sounds like you really know your glaze chemistry. I'm afraid I'm more
than a tad lacking in comprehension re: behavior of each of the compounds &
their relation to others.
There really haven't been any changes in my firing / cooling rate profile,
although when I first tried this glaze, I was using an old 2" brick Skutt 18"
electric kiln. I later got into the extra-insulated Bailey (Cone Art) 18"
kiln w/Envirovent, and obtained a couple more good firings after the switch
over. And the problem has gotten more bizarre since I can't even get the
glaze to stay on the bisqueware to get it into the kiln for firing -- go
figure!
As far as glaze ingredient reformulation goes -- Would you mind offering any
specific recomendations?
Sheilah Bliss
Bliss Pottery
BlissPots@aol.com
MRS SANDRA L BURKE on sun 26 jul 98
Ron,
I have been following the discussion on "Neurotic glaze-help". I have
been researching glazes-especially those that break or have textured
surfaces and have found that alot of formulas contain lithium.
Lithium, is something I try very hard to stay away from because of
all the warning lables that accompany it. Although I have been
involved in ceramics for a long time, I am afraid that my knolwedge
of glazes and glaze calculation is limited.
Why do so many of these breaking/textured glazes call for lithium?
What could one use instead?
Thanks,
Sandy Burke
Ron Roy on wed 29 jul 98
----------------------------Original message----------------------------
Hi Sandy,
Glad you asked - been wanting to talk about this for a while now.
If you look at a potters periodic table - see the Hamer book - page 242 in
the latest edition - you will see Li20, K2O, and Na2O all grouped together
at the far left - many of the more technical pottery books have the same
table.
You can also see all three grouped together on any list that describes the
oxides we use in glaze making in terms of viscosity and surface tension.
They are at the low end of those lists - meaning they are runners.
This all means - if there are not enough other oxides present in a glaze to
counteract their propensity to run off the pot - they will. The quickest
way to stop the running is to get more Alumina into the glaze. Al2O3 is at
the top of both lists and has the highest viscosity and surface tension of
all the oxides we use.
In the days before so many of us were using calculation to count the number
of each molecules in a glaze - we had to guess what would work to get a
glaze to run more. The usual answer would be - get more K2O or Na2O into
the glaze (or lower the alumina.) But there were two problems with that.
First - our KNaO normally comes in feldspar or frit and both had other
oxides with them. Made it practically impossible if you were guessing
about the number of molecules you were adding.
Potassium and Sodium also have the highest rate of expansion and
contraction - so crazing became a problem as well.
The simplest way to get more running and/or more melting was to simply add
some lithium carbonate. Lithium has a lower rate of expansion than the KNaO
under some circumstances as well. So it seemed like a straight forward
answer that anyone could handle.
There are three problems with this approach. First of all lithium carb is
slightly soluble in water and it is a deflocculant. This means - under the
some circumstances - if there is enough present - the glaze will settle
out. Using soluble materials in a glaze had the disadvantage of the
solubles crystallizing out in the bucket - not a desirable situation.
If you have enough lithium carb in a glaze you can have serious fit
problems - especially if there is no KNaO present. Very low expansion
glazes are made this way and they will shiver off bodies which are not
designed to co-exist with them.
The third problem lies in the toxicity of Lithium carb. Lithium is used as
a drug to help manic depression - in very small, regulated doses. If glazes
are not formulated to be durable this can be a problem. Unlike sodium and
potassium lithium has toxicity implications.
It is not a difficult job to make safe runny glazes if you are counting
molecules - I am tempted to say quite easy if you have some understanding
of the role of oxides in glazes and especially if you use a computer to do
the calculations for you. I know this is a fearsome area for many potters -
all I can say is - if I can learn to do it just about anyone else can. I
wish those of you who think you can't would be able to see how quickly even
those, who are petrified at the thought, can be calculating their own
glazes after only a few days in the lab.
I have to add here that the old way of making glazes - try hundreds of
mixtures and pick the ones that look best - does not give information in
two important areas - expansion/contraction and durability. When you "get"
a glaze you will probably have to either guess about these two important
aspects, test the glaze for both and/or calculate it to have some
indication of what to expect. The only accurate way is to test the glaze on
each of the bodies you use.
Further to the conversation about buying from the cheapest supplier - It
costs to test clays - when you make your decision about where to buy them -
think about quality control - or test each batch yourself - each time.
>I have been following the discussion on "Neurotic glaze-help". I have
>been researching glazes-especially those that break or have textured
>surfaces and have found that alot of formulas contain lithium.
>Lithium, is something I try very hard to stay away from because of
>all the warning lables that accompany it. Although I have been
>involved in ceramics for a long time, I am afraid that my knolwedge
>of glazes and glaze calculation is limited.
>Why do so many of these breaking/textured glazes call for lithium?
>What could one use instead?
>Thanks,
>Sandy Burke
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
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