Brenda Z on wed 12 dec 01
At the Potters' Guild where I am a member, we are
trying to find a new set of cone 6 oxidation
studio glazes. We are using several different
clay bodies, bisqued to cone 06. Our primary
concerns are that our glazes be food safe and
stable.
After testing a lot of different base glazes, we
settled on Tony Hansen's base glaze with
colourants. As suggested on the Digitalfire web
site, we added 10% superpax to get a white glaze.
Unfortunately this glaze crawls wherever it meets
any of our coloured glazes (the ones that use the
T.H. base).
The recipe we are using is:
Wollastonite 20
FRIT 3134 20
E.P.K 20
Silica 20
Potash Feldspar 20
Bentonite 2
Superpax 10
Unfortunately, we have no glaze gurus in the
guild, so our best guess is to test the glaze with
different opacifiers, and to test with varying
amounts of opacifier. Are we on the right track?
We have ruled out dust as a cause of the crawling,
since the problem occurs whether or not the bisque
is washed before glazing. The problem also occurs
mostly where the two glazes are layered.
Thanks,
Brenda Z
http://www.potter.ca
Ababi on thu 13 dec 01
This Glaze of Tony Hansen has the advantage of rounded numbers. I will
be very carful with my limit knowledge and with my experience with this
glaze.
a) I think it should applied on the thinner side otherwise it is not
delicate look
Now, The supperpax has about 35% silica.
I add here to make it shorter only the analysis
First 20/5 of Hansen
CaO 0.77* 13.84%
MgO 0.01* 0.07%
K2O 0.12* 3.54%
Na2O 0.11* 2.09%
TiO2 0.00 0.08%
Al2O3 0.36 11.74%
B2O3 0.21 4.66%
P2O5 0.00 0.05%
SiO2 3.32 63.70%
Fe2O3 0.00 0.23%
Si:Al 9.21
SiB:Al 9.79
Expan 7.18
Now with the supperpax See the silica, silica alumina and expansion.
CaO 0.77* 12.58%
MgO 0.01* 0.06%
K2O 0.12* 3.21%
Na2O 0.11* 1.90%
TiO2 0.00 0.07%
ZrO2 0.17 6.08%
Al2O3 0.36 10.66%
B2O3 0.21 4.23%
P2O5 0.00 0.04%
SiO2 3.49 60.95%
Fe2O3 0.00 0.21%
Si:Al 9.70
SiB:Al 10.28
Expan 6.76
To be honest I do not understand the numbers all the way.
Yet I will adjust it in a way that the add you will have will be the
Zircon by itself
Wolastonite........ 20.00 18.40%
FRIT 3134........... 20.00 18.40%
E.P.K............... 20.00 18.40%
Silica.............. 16.70 15.36%
Potash Feldspar..... 20.00 18.40%
Bentonite........... 2.00 1.84%
Superpax............ 10.00 9.20%
=3D=3D=3D=3D=3D=3D=3D=3D
108.70
CaO 0.77* 12.97%
MgO 0.01* 0.06%
K2O 0.12* 3.31%
Na2O 0.11* 1.96%
TiO2 0.00 0.07%
ZrO2 0.17 6.27%
Al2O3 0.36 10.99%
B2O3 0.21 4.37%
P2O5 0.00 0.05%
SiO2 3.32 59.74%
Fe2O3 0.00 0.22%
Cost/kg 1.26
Si:Al 9.22
SiB:Al 9.80
Expan 6.86
Or you can do the base with 5 to 10 tin
Or try this one
You can try this glaze too. I find it very reliable at ^6 From the
clayart database at the ceramicweb
Glaze Name: Clear (Huddleston)
cone: 5 - 6
color: transparent clear
surface:glossy, shiny
50.00 Ferro Frit 3134
30.00 EPK
20.00 Silica
100.00 % Totals:
estimated thermal expansion: 70.79x10-7/=B0C
Unity Formula for Clear (Huddleston):
0.004 K2O 0.419 Al2O3 3.596 SiO2
0.313 Na2O 0.626 B2O3 0.004 TiO2
0.679 CaO 0.004 Fe2O3 8.6:1 Si:Al Ratio
0.004 MgO
Percentage Analysis for Clear (Huddleston):
59.81 % SiO2
11.83 % Al2O3
12.04 % B2O3
0.11 % K2O
5.37 % Na2O
10.54 % CaO
0.04 % MgO
0.18 % Fe2O3
0.09 % TiO2
Ababi Sharon
Kibbutz Shoval- Israel
Glaze addict
ababisha@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
http://www.israelceramics.org/
---------- Original Message ----------
>At the Potters' Guild where I am a member, we are
>trying to find a new set of cone 6 oxidation
>studio glazes. We are using several different
>clay bodies, bisqued to cone 06. Our primary
>concerns are that our glazes be food safe and
>stable.
>After testing a lot of different base glazes, we
>settled on Tony Hansen's base glaze with
>colourants. As suggested on the Digitalfire web
>site, we added 10% superpax to get a white glaze.
>Unfortunately this glaze crawls wherever it meets
>any of our coloured glazes (the ones that use the
>T.H. base).
>The recipe we are using is:
>Wollastonite 20
>FRIT 3134 20
>E.P.K 20
>Silica 20
>Potash Feldspar 20
>Bentonite 2
>Superpax 10
>Unfortunately, we have no glaze gurus in the
>guild, so our best guess is to test the glaze with
>different opacifiers, and to test with varying
>amounts of opacifier. Are we on the right track?
>We have ruled out dust as a cause of the crawling,
>since the problem occurs whether or not the bisque
>is washed before glazing. The problem also occurs
>mostly where the two glazes are layered.
>Thanks,
>Brenda Z
>http://www.potter.ca
>_______________________________________________________________________
_
>______
>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.
Paul Taylor on fri 14 dec 01
Dear Breda
What is happening is that the glaze is too viscous. It has a greater
surface tension than the glazes it is put on. What happens then is that any
disturbance of the glaze surface before or during firing the glaze will
gather in on its self rather than heal over. Some glazes particularly high
iron ones sometimes called tenmocu will melt the opecifyed glaze enough to
settle it down into a leopards skin type effect.
Tenmocus are quite fluid glazes and a more stable glaze or a thin glaze is
just enough lubrication to make the glaze crawl but not fluid enough to heal
the glaze over again, and or your top temperature is not hot enough to melt
the glazes well. Cone 8 to 9 gives you greater margins of error.
Like most glaze technology it is a balancing act Tony,s glazes are
probably great for not running all over the place easy to control and
underglaze or overglaze decoration does not run with the glaze to the bottom
of the pot. so the fluidity of the glaze is quite low. But there is enough
lubrication to crawl a viscose upper glaze. If you look at water on a
plastic table and compare it with one with wax on or butter you will
immediately see what i mean. Worse some times the viscose glaze will get
very insulting and gather the more fluid under glaze up with it.
Firstly do you expect to be using this glaze on any other glaze but a
temocu. its not very usual - white is the one you put on first for miolica
work and to show off colored glazes. i suspect your white will very good at
that so you may be better off constructing a white that works differently
for top dipping.
I will suggest several things and doing all of them may be needed to fix
the problem if it can be fixed
If you could halve the super pax that would help - I use 5% zirconium
silicate if you have to use 10% of your stuff it better be less than half
the price of zirconium or its not worth it; or maybe it is designed to be a
better opacifyer and 5% should do. this should make the glaze less viscose
And the EPK Which I suppose to be a china clay could be replaced with a ball
clay. The advantage of this is that a ball clay has a smaller particle size
and will help with the glaze strength and also flux a little better and make
the glaze more runny it may not help the viscosity but it should make the
glaze more fluid so it flows a bit . This could of course make matters worse
but a more fluid glaze can help . If you want you can replace the china
clay with all /some siliceous ball clay this will increase the silica and
lower the alumina ( alumina is very viscose) with out disturbing any other
proportions. If the glaze shivers you are in trouble. But that is so
unlikely to happen I was reluctant to mention it.
The bentionite is there to help the raw glaze strength and maybe 2% is a
useless amount in the face of so much opacifuyer of large particle size. the
ball clay should take care of those problems but if you only have an
aluminus ball clay you could replace some of the ball clay with a bit of
bentonite so that would leave you with 5% bentonite 17 % clay. The ball clay
could dull the color slightly especially if the glaze is under fired so
there is no need to sub all the china clay, but my white is very white and
bright and it has no china clay . I use a mixture of ball clays to control
expansion - and it covers any thing.
Glazes crack and then crawl on the biscuit pot for two reasons. firstly
not enough fine particles - like your glaze - so there is no elasticity when
you dip the biscuit - a little flocculant like vinegar can help. However
the opposite can occur with too much plastic clay - too much shrinkage- and
the glaze cracks in spite of the elasticity and strength. Then you have to
defloculate or calcine the clay or use china clay. So you can see as always
there is a happy medium with about 15% plastic clay . With 15% plastic clay
you can do murder - grind the glaze all you like and its a dream to put on
and if it curtains and runs you can thicken it with vinegar,- but do not
over do the flocculant( vinegar) as you get cracking and crawling again.
I have no idea what frit you are using. It is there to bring the glaze
down to cone 6 with out crazing so I would leave it alone. unless you are
going to break down the recipe into a formula and work from there.
There seems to be the right amount of calcium, and walistonite is always a
good choice.
Again I hate to be discouraging but i think the best you could hope for is
the glaze crawling over the color and rehealing when it becomes involved
with the fluid glaze underneath giving a mottled or leopards skin effect so
the bottom glaze will have to be thicK and quite fluid to melt the top glaze
into it - like a tenmocu does very well. A less viscose glaze will be more
harmonious but I would expect a little crawling but not so much that the
integrity of the underneath glaze is totally destroyed and shows bare
patches.
I could have broken down the glaze chemicaly but there are people champion
that methodologie with fancy computer programs. I have given you the
empirical approach however the chemical one is just as valid if not more so
- depending on your self.
--
Regards Paul Taylor
> From: Brenda Z
> Reply-To: Brenda Z
> Date: Wed, 12 Dec 2001 22:27:31 -0500
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Glaze Crawling Problems
>
> At the Potters' Guild where I am a member, we are
> trying to find a new set of cone 6 oxidation
> studio glazes. We are using several different
> clay bodies, bisqued to cone 06. Our primary
> concerns are that our glazes be food safe and
> stable.
>
> After testing a lot of different base glazes, we
> settled on Tony Hansen's base glaze with
> colourants. As suggested on the Digitalfire web
> site, we added 10% superpax to get a white glaze.
> Unfortunately this glaze crawls wherever it meets
> any of our coloured glazes (the ones that use the
> T.H. base).
>
> The recipe we are using is:
> Wollastonite 20
> FRIT 3134 20
> E.P.K 20
> Silica 20
> Potash Feldspar 20
> Bentonite 2
> Superpax 10
>
> Unfortunately, we have no glaze gurus in the
> guild, so our best guess is to test the glaze with
> different opacifiers, and to test with varying
> amounts of opacifier. Are we on the right track?
>
> We have ruled out dust as a cause of the crawling,
> since the problem occurs whether or not the bisque
> is washed before glazing. The problem also occurs
> mostly where the two glazes are layered.
>
> Thanks,
> Brenda Z
> http://www.potter.ca
>
> ______________________________________________________________________________
> 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.
Ron Roy on mon 17 dec 01
Hi Brenda,
First of all do not assume this glaze is stable - that depends on a number
of factors one of which is - how much coloring oxide are you adding - make
sure you at least do the vinegar test on those variations.
Many times the way to get rid of crawling is to exchange a stronger clay
for the kaolin in the glaze.
I should add that I do not agree that calcining some of the clay in a glaze
to stop crawling as the best way to stop the problem. I have had much
better success by improving the strength of the glaze using "better" (those
with higher MOR) clays.
As an example - I have done some work with one of Jeff Oestreich's slips
and it stuck to all stages just fine - 95% Bell Dark Ball clay and 5% Red
Iron oxide. Yes I was amazed - after all hadn't the books all said it
problem was shrinkage. So I recommend other solutions now and from the lack
of complaints I have to assume good results.
It is also possible to minimize the problem by only firing your glazes
after they are dried normally - in other words not fired wet. It is also
possible to get around some of these problems by not allowing the base
glaze to dry completely before applying the second coat. I assume this
works because dry glaze is powdery (especially if it's made with kaolin)
and this interferes with the top glaze getting a good grip.
Anyway - I have reformulated this glaze - do some 500 gram tests and you
may have your solution.
If anyone says - but the numbers are all different - it's harder to weigh
out - tell em from me - anyone choosing a glaze because it's easy to weigh
out should take up painting by numbers - they have no business being in a
pottery studio.
I think I will excuse my mood this evening by blaming it on the printers -
it's the stress of publishing folks - even thought everything is going
fine.
Cone 6 Hansen 20x5 base revised by RR
G200 - 18.0 (can use Custer)
Wolas - 19.5
F3134 - 19.5
OM#4 - 28.0 (I can do this with any ball clay if I have the analysis)
Silica - 15.0
Total - 100.0
I suggest trying it with and without the bentonite - examine the dry
applied glaze with a magnifier to see which is better - fewer cracks and/or
harder surface.
There are solubles that can be added to glazes that will certainly help - I
prefer to not use them unless absolutely necessary - there is always a
price to pay.
RR
>At the Potters' Guild where I am a member, we are
>trying to find a new set of cone 6 oxidation
>studio glazes. We are using several different
>clay bodies, bisqued to cone 06. Our primary
>concerns are that our glazes be food safe and
>stable.
>
>After testing a lot of different base glazes, we
>settled on Tony Hansen's base glaze with
>colourants. As suggested on the Digitalfire web
>site, we added 10% superpax to get a white glaze.
>Unfortunately this glaze crawls wherever it meets
>any of our coloured glazes (the ones that use the
>T.H. base).
>
>The recipe we are using is:
>Wollastonite 20
>FRIT 3134 20
>E.P.K 20
>Silica 20
>Potash Feldspar 20
>Bentonite 2
>Superpax 10
>
>Unfortunately, we have no glaze gurus in the
>guild, so our best guess is to test the glaze with
>different opacifiers, and to test with varying
>amounts of opacifier. Are we on the right track?
>
>We have ruled out dust as a cause of the crawling,
>since the problem occurs whether or not the bisque
>is washed before glazing. The problem also occurs
>mostly where the two glazes are layered.
>
>Thanks,
>Brenda Z
>http://www.potter.ca
>
>______________________________________________________________________________
>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.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
iandol on tue 18 dec 01
Dear Ron Roy,
You say <stronger clay for the kaolin in the glaze.>>
You pique my bump of inquisitiveness.
Please elaborate on the notion of a "Stronger Clay".
Best regards,
Ivor Lewis
Christena Schafale on tue 18 dec 01
I must respectfully disagree with Ron on this one, at least based on my own
experience. In my nightmare first year of mixing glazes, I tried every
ball clay I could get my hands on, based on Ron's advice, and still found
that glazes with more than 15% or so of raw clay cracked, peeled, and
crawled. So Ron's solution may work for some people, but it didn't work
for me. Calcining the clay was the only thing that worked.
Chris
>I should add that I do not agree that calcining some of the clay in a glaze
>to stop crawling as the best way to stop the problem. I have had much
>better success by improving the strength of the glaze using "better" (those
>with higher MOR) clays.
>
>So I recommend other solutions now and from the lack
>of complaints I have to assume good results.
Light One Candle Pottery
209 N Woodrow St
Fuquay-Varina, NC 27526
(919) 567-1098
candle@intrex.net
www.lightonecandle.com
Fredrick Paget on tue 18 dec 01
If I remember correctly, Karl Platt posted a message that said that
tungsten oxide acts like a wetting agent in a glaze and reduces the surface
tension. If this is so, maybe that would cure this problem.
Since I have some tungsten oxide and I have some bay mud from Gallinas
creek that makes a slip glaze
that crawls miserably I will run a test in a few weeks when school starts
up again to see if it is any use.
Fred Paget
>If I remember correctly, this question originated from a post about Tony
>Hansen's 5X20 cone 6 glaze. Without Zircopax it was fine, with Zircopax
>crawling reared it's ugly head.
........(SNIP).............
................................................................................
............ The idea is to
>lower the surface tension when the glaze is melted.
>
>regards, Craig Martell in Oregon
From Fred Paget, Marin County, California, USA
Craig Martell on tue 18 dec 01
Hi there:
If I remember correctly, this question originated from a post about Tony
Hansen's 5X20 cone 6 glaze. Without Zircopax it was fine, with Zircopax
crawling reared it's ugly head.
I think Paul Taylor has already addressed the "surface tension" root of
this particular fault. It's my opinion that Paul is right on the
money. But, may I add my own thoughts on the subject?
Zircon has an extremely high surface tension. I think it's number 3 on the
list with alumina and silica being higher. As I remember, Tony's glaze is
right up there with alumina and silica and the addition of 10% zircopax is
pushing this glaze over the edge with surface tension and crawling. The
crawling is taking place in the kiln after the glaze sinters. When it
reaches maturation temp, there's so much surface tension that the glaze
won't flow back and heal.
Possible remedies are: Decrease the zircopax as much as you can while
maintaining the whiteness that you want. Increase the potash feldspar a
bit. (Potassium is a "wetting agent" and has the lowest surface tension of
any fluxing oxide we use). Decrease the alumina (kaolin) a bit. You need
to be careful with this so you don't get too low and when you drop the clay
content you are decreasing silica too. A glaze calc program is worth it's
weight in cobalt for this.
Anyway, those are some of the things I would try. If one adjustment
doesn't do the job, try a combo of two or three things. The idea is to
lower the surface tension when the glaze is melted.
regards, Craig Martell in Oregon
Ron Roy on mon 24 dec 01
Hi Chris,
Thanks for posting this - it is important that we all understand -
situations and materials are different and it is rare that one solution is
the answer for all problems.
I have wondered about why I could not solve your problem the way I usually
do. I have to add - I have solved an awful pile of crawling problems by
simply changing clays in the glaze recipe. In fact - as far as I know yours
was the only situation that was not.
Has anyone else had to calcine clay having after having tried subbing in
clays with higher MOR's?
RR
>I must respectfully disagree with Ron on this one, at least based on my own
>experience. In my nightmare first year of mixing glazes, I tried every
>ball clay I could get my hands on, based on Ron's advice, and still found
>that glazes with more than 15% or so of raw clay cracked, peeled, and
>crawled. So Ron's solution may work for some people, but it didn't work
>for me. Calcining the clay was the only thing that worked.
>
>Chris
>
>
>>I should add that I do not agree that calcining some of the clay in a glaze
>>to stop crawling as the best way to stop the problem. I have had much
>>better success by improving the strength of the glaze using "better" (those
>>with higher MOR) clays.
>>
>>So I recommend other solutions now and from the lack
>>of complaints I have to assume good results.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Ron Roy on mon 24 dec 01
Now this might sound as if I'm disagreeing with Craig - I am not - what he
says is gold - take it to the bank.
What I am saying is:
Background - most glazes crack up to some degree - you can sometimes see it
with a magnifying glass when the glaze is dry on the ware - before
stacking. If it starts there you know it may be a serious problem -
especially if the glaze has - from a chemical point of view - either high
surface tension or high viscosity - (means stiff not runny.)
If they don't start to crack up dry many start to crack up during the
beginning of the glaze firing. If the cracks open up enough and the glaze
is too stiff - they never get back together again - and some bare clay is
visible.
What we don't understand about this process is that most glazes do crack up
but heal over at the end of the glaze fire when the glaze can flow back
together.
We can reformulate our recipes to help reduce the cracking - many times we
can stop it completely - and still have our stiff clay mattes.
On the other hand - those who rely on crawling as a decorative effect - or
like Tony C - just to annoy others - can promote it by again, manipulating
the recipe.
Like all glaze understanding - it can be used to backwards or forward and
even sideways.
RR
>If I remember correctly, this question originated from a post about Tony
>Hansen's 5X20 cone 6 glaze. Without Zircopax it was fine, with Zircopax
>crawling reared it's ugly head.
>Anyway, those are some of the things I would try. If one adjustment
>doesn't do the job, try a combo of two or three things. The idea is to
>lower the surface tension when the glaze is melted.
> from Craig
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Ron Roy on mon 24 dec 01
Dear Ivor,
I thinkyour bump is a mountain - and I for one am grateful for it.
Stronger clays: I can get - many times - from the mine MOR (modulus of
rupture) of dry clay numbers from the mine. They usually come as 50% clay
&50% silica.
I'm going to quote some in a post - probably tomorrow.
I have found that replacing a clay in a crawling glaze with another clay
that has a higher MOR will make the glaze more resistant to cracking during
drying and firing. This is especially so when replacing a kaolin with ball
clay - you need more ball to get the same amount alumina so you actually
get more binder and a better one.
RR
>You say <>stronger clay for the kaolin in the glaze.>>
>
>You pique my bump of inquisitiveness.
>
>Please elaborate on the notion of a "Stronger Clay".
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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