John Hesselberth on wed 10 jan 01
Susan Saunders wrote:
>it, clumps up into dozens of small, rock-like shards that I'm unable to deal
>with. Can someone tell me why this happens, and if there's anything I can do
>to prevent it? I like the glaze itself very much.
>
>Matte green glaze, Cone 6
>neph sy 40
>epk 10
>flint 14
>gerstley 10
>lith carb 8
>whiting 8
>titanium 10
>
>copper carb 3%
>bentonite 2%
>
>Thanks for any advice.
>
>Susan, in the frozen Northeast
Hi Susan,
You didn't say how you are mixing. Are you screening it? If not, you
should. Use an 80 mesh screen and put the glaze through it at least
twice. Some glazes take 3 or 4 passes before they are smooth. Or if you
are mixing small batches--say 1000grams or less--try using a blender that
you dedicate to your pottery studio. The bearings on the blender may not
last long, but it can be a pretty effective glaze mixer.
As an aside, this glaze will not be very stable. It does not have enough
silica. I doubt that it will pass the vinegar test. Using lithium
carbonate as a source of lithium can also cause problems. It is
sufficiently soluble that you may get variable concentrations with time
or even on the same pot. If you are using it on sculptural work it may
be OK, but I wouldn't use it on functional work without testing it pretty
thoroughly.
Regards, John
"The life so short, the craft so long to learn." Hippocrates, 5th cent.
B.C.
Susan Saunders on wed 10 jan 01
I'm a neophyte when it comes to glaze recipes. Some I've gotten from Clayart
archives, others from friends, mostly Cone 6 oxidation. I have a recipe for a
sort of Arts-and-Crafts matte green Cone 6 glaze that, as soon as I've mixed
it, clumps up into dozens of small, rock-like shards that I'm unable to deal
with. Can someone tell me why this happens, and if there's anything I can do
to prevent it? I like the glaze itself very much.
Matte green glaze, Cone 6
neph sy 40
epk 10
flint 14
gerstley 10
lith carb 8
whiting 8
titanium 10
copper carb 3%
bentonite 2%
Thanks for any advice.
Susan, in the frozen Northeast
Susan Saunders on thu 11 jan 01
Thanks so much for your reformulation for the green glaze, and also for the
advice about keeping it warm--it has indeed been a cold winter, and the
garage that it's stored in is heated, but barely. I use the glaze for outdoor
sculpture, not on functional pots. Thus far it hasn't crazed on the clay that
I'm using, a commercial grogged body. And of course I won't attach your name
to it. Actually, it already has a name: Val's Matte Green.
Again, thank you--I'm making garden pillars, and this green is perfect for
them.
Susan
Lorraine Pierce on thu 11 jan 01
Hi Susan, perhaps it would help us to help you if you could explain how you
store, mix and sieve your glaze materials. Have any of your materials
clumped in the bag? I once recieved a bag of a materials that was not
properly milled, therefore was not fine enough to go thru my sieve. First
check each material.
My usual proceedure for a 5000 gram batch or more would be to weigh out all
the ingredients into a dry container, then slake them overnight in another
container, adding the materials TO the water in the second container as
one does when mixing plaster. The next morning I sieve the slurry thru the
glaze sieve, and if necessary adjust the water in the batch. BENTONITE CAN
EASILY CLUMP IF YOU ARE NOT CAREFUL. Some potters always mix the bentonite
and water in a blender and keep the solution on hand, pre-mixed, to add to
the glaze batch. I find that the slaking method works for me; DO NOT mix
the water and materials in any way when putting them to slake...just add
them to the water, making a little 'mountain' of the materials and let
nature do its thing. Hope this helps. Lori in New Port Richey Fl.
Martin Howard on thu 11 jan 01
Susan, how did you mix it?
If you put the bentonite into the water by itself, or on top of the other
ingredients in a liquid state, then it will clump. Mix them all dry first.
Then add the water.
Others may have other ideas, but that is the first one that comes to mind,
using cat litter everyday.
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
Ababi Sharon on thu 11 jan 01
Hello Susan in the north east!
On Sunday, mix the bentonite with warm water, the amount you need for the
whole glaze,mix it with an electric mixer.
On Monday, add to it the rest of the glaze.
Ababi in the middle of the east.
http://www.milkywayceramics.com/cgallery/asharon.htm
http://www.israelceramics.org/index.html
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ID: sharon@shoval.org.il
Password:clay
----- Original Message -----
From: "Susan Saunders"
To:
Sent: Wednesday, January 10, 2001 8:49 PM
Subject: rocks in glaze
> I'm a neophyte when it comes to glaze recipes. Some I've gotten from
Clayart
> archives, others from friends, mostly Cone 6 oxidation. I have a recipe
for a
> sort of Arts-and-Crafts matte green Cone 6 glaze that, as soon as I've
mixed
> it, clumps up into dozens of small, rock-like shards that I'm unable to
deal
> with. Can someone tell me why this happens, and if there's anything I can
do
> to prevent it? I like the glaze itself very much.
>
> Matte green glaze, Cone 6
> neph sy 40
> epk 10
> flint 14
> gerstley 10
> lith carb 8
> whiting 8
> titanium 10
>
> copper carb 3%
> bentonite 2%
>
> Thanks for any advice.
>
> Susan, in the frozen Northeast
>
>
____________________________________________________________________________
__
> 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.
Judith S. Labovitz on thu 11 jan 01
in my rather limited experience in making batch glazes using bentonite I
have found it useful to do a variation on this...I mix small amounts
bentonite (dry) into the larger stuff going in (ie 3000 grams of
feldspar or whatever) it seems to diffuse better that way I have no clumping.
judy
At 04:44 AM 1/11/01 -0500, you wrote:
>Hi Susan, perhaps it would help us to help you if you could explain how you
>store, mix and sieve your glaze materials. Have any of your materials
>clumped in the bag? I once recieved a bag of a materials that was not
>properly milled, therefore was not fine enough to go thru my sieve. First
>check each material.
>
>My usual proceedure for a 5000 gram batch or more would be to weigh out all
>the ingredients into a dry container, then slake them overnight in another
>container, adding the materials TO the water in the second container as
>one does when mixing plaster. The next morning I sieve the slurry thru the
>glaze sieve, and if necessary adjust the water in the batch. BENTONITE CAN
>EASILY CLUMP IF YOU ARE NOT CAREFUL. Some potters always mix the bentonite
>and water in a blender and keep the solution on hand, pre-mixed, to add to
>the glaze batch. I find that the slaking method works for me; DO NOT mix
>the water and materials in any way when putting them to slake...just add
>them to the water, making a little 'mountain' of the materials and let
>nature do its thing. Hope this helps. Lori in New Port Richey Fl.
>
>______________________________________________________________________________
>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.
Wade Blocker on thu 11 jan 01
Susan,
Do you mix the dry bentonite thorougly into your glaze before adding
water, and only then screening the glaze? Mia in sunny ABQ
Ron Roy on thu 11 jan 01
Both Neph Sy, Lithium carb and GB are partly soluble - it is probably these
salts that are combining with each other and also salts in your water
supply to form crystals. Take a look at those "rocks" with a good magnifier
- you may be able to see the crystals.
Keeping the glaze warm may dissolve them.
Better to reformulate using less soluble materials. Here is my
reformulation - Custer spar should work as well if you don't have G200.
This glaze has a lit of Lithium Carb and that can be problematic - test
well for fit. As others have noted - it's not a durable glaze - especially
with the copper addition. I think it would be foolish to use it inside
functional pots. It's going to craze on most cone 6 bodies. If you give the
recipe away make sure a note is attached saying it's not good for contact
with food - and don't attach my name to it - it is not a glaze I would ever
recommend.
Calculated expansion and ratio are close to the original.
-----------------
G 200 SPAR.......... 44.50
F3134............... 13.50
LITH CARB........... 9.00
WHITING............. 8.00
TALC................ 2.00
EPK................. 18.00
SILICA.............. 5.00
TIO2................ 11.00
----------
111.00
FORMULA & ANALYSIS
------------------
*CaO........ .37 7.73%
*Li2O....... .33 3.65%
*MgO........ .04 .65%
*K2O........ .14 4.86%
*Na2O....... .12 2.76%
Fe2O3...... .00 .18%
TIO2....... .38 11.14%
B2O3....... .12 3.14%
AL2O3...... .40 15.06%
SiO2....... 2.27 50.81%
P2O5....... .00 .02%
RATIO 5.74 (org is 5.65)
EXPAN 606.56 (org is 602.92)
WEIGHT 268.44 (org is 263.71)
>I'm a neophyte when it comes to glaze recipes. Some I've gotten from Clayart
>archives, others from friends, mostly Cone 6 oxidation. I have a recipe for a
>sort of Arts-and-Crafts matte green Cone 6 glaze that, as soon as I've mixed
>it, clumps up into dozens of small, rock-like shards that I'm unable to deal
>with. Can someone tell me why this happens, and if there's anything I can do
>to prevent it? I like the glaze itself very much.
>
>Matte green glaze, Cone 6
>neph sy 40
>epk 10
>flint 14
>gerstley 10
>lith carb 8
>whiting 8
>titanium 10
>
>copper carb 3%
>bentonite 2%
>
>Thanks for any advice.
>
>Susan, in the frozen Northeast
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Louis Katz on fri 12 jan 01
>
The shards are most likely lithium borate crystals. The come about when Gertsley
and Litithium carb sit in the same glaze for a few months. I suppose it might
happen faster. If you crush them up in a mortar a pestle (they are hard) they will
probably just grow big again in a few weeks. Ron Roys advice is the ticket.You
probably could just get rid of the soluble Lithium if keeping Gertsley is
necessary.
I removed tLithium Borate crystals from a raku glaze. Since Lithium and boron
provided the umph to melt the resulting glaze did not melt until near cone ten. We
tend to think of things as being static in the glaze bucket. A fine assumption
most of the time.
Louis
>
> >it, clumps up into dozens of small, rock-like shards that I'm unable to deal
> >with. Can someone tell me why this happens, and if there's anything I can do
> >to prevent it? I like the glaze itself very much.
> >
> >Matte green glaze, Cone 6
> >neph sy 40
> >epk 10
> >flint 14
> >gerstley 10
> >lith carb 8
> >whiting 8
> >titanium 10
> >
> >copper carb 3%
> >bentonite 2%
> >
> >Thanks for any advice.
> >
> >Susan, in the frozen Northeast
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