Kathy Addy on tue 9 jun 98
The following Cone 6 electric glaze was a beautiful no-problem glaze first =
time
we tried it at the (now defunct) Potters Guild in Atlanta. The second batch=
and
my own subsequent batch have exhibited problems of crawling. The glaze just
seems to let go in spots regardless of how careful I am in surface =
preparation.
Can anyone out there suggest a reason this might happen?
Nepheline syenite 31.11
Wollastonite 22.22
Gerstley Borate 17.78
Zircopax 12.22
Kaolin 11.11
Silica 5.56
Copper Carb 3.00
Bentonite 2.00
(I always add a squirt of pre-mix CMC too.)
Grateful for your feedback.
K.
John Post on thu 11 jun 98
At 08:49 AM 6/9/98 EDT, you wrote:
>----------------------------Original message----------------------------
>The following Cone 6 electric glaze was a beautiful no-problem glaze first
time
>we tried it at the (now defunct) Potters Guild in Atlanta. The second
batch and
>my own subsequent batch have exhibited problems of crawling. The glaze just
>seems to let go in spots regardless of how careful I am in surface
preparation.
>Can anyone out there suggest a reason this might happen?
Hi Kathy,
It's the gerstley borate in your glaze that's causing the problems. I try
not to have over 10% in my cone 6 glazes.
At the local community college where I work the students were always having
trouble with glazes crawling. The glazes that crawled most frequently had
20% or more gerstley in them. We reformulated the glazes using frit 3134
instead of the g.b. and eliminated the crawling.
Your original glaze is low in silica, that is if you want it to be a good
foodsafe durable glass.
I revised your glaze two different ways using Glazchem software. The first
revision is an attempt to keep the glaze character the same but replaces
the gerstley borate with frit 3134. In the second version I kicked up the
silica to the low end of the limit formula range. This may give you a more
durable glaze. The silica can go even higher, but this will change the
look of the glaze even more and only you can determine what your goal with
this glaze is.
If you decide to test either one of these glazes, let me know how they work
out for you.
+++++++++++++++++++++++++++++
+++ Glaze that crawls +++
+++++++++++++++++++++++++++++
Date: 06/11/98
Nepheline syenite 31.11 31.1%
Wollastonite 22.22 22.2%
Gerstley borate 17.78 17.8%
Zircopax 12.22 12.2%
EPK 11.11 11.1% Hazard!
Flint 5.56 5.6% Hazard!
-------- ------
100 100 %
Copper carbonate 3 3 % Hazard!
Bentonite 2 2 % Hazard!
===========================
Chemical Analysis
===========================
Na2O 0.18 Al2O3 0.33 SiO2 2.09
K2O 0.04 B2O3 0.20 TiO2 0.00
MgO 0.07 Fe2O3 0.00
CaO 0.65 ZrO2 0.18
CuO 0.06
Alumina:Silica ratio is 1.00 : 6.42
Neutral:Acid ratio is 1.00 : 4.35
Alkali:Neutral:Acid ratio is 1.00 : 0.52 : 2.27
Expansion coefficient: 81.0 x 10e-7 per degree C
Oxides causing abnormal expansion effects: B2O3
++++++++++++++++++++++++++++
+++ Modified glaze 1 +++
++++++++++++++++++++++++++++
Date: 06/11/98
Frit 3134 23.4 23.4%
Nepheline syenite 22.3 22.3%
Wollastonite 21.8 21.8%
Talc 2.2 2.2% Hazard!
EPK 18.3 18.3% Hazard!
Zircopax 12 12 %
-------- ------
100 100 %
Copper carbonate 3 3 % Hazard!
Bentonite 2 2 % Hazard!
===========================
Chemical Analysis
===========================
Na2O 0.19 Al2O3 0.33 SiO2 2.11
K2O 0.03 B2O3 0.20 TiO2 0.00
MgO 0.07 Fe2O3 0.00
CaO 0.65 ZrO2 0.16
CuO 0.06
Alumina:Silica ratio is 1.00 : 6.48
Neutral:Acid ratio is 1.00 : 4.37
Alkali:Neutral:Acid ratio is 1.00 : 0.52 : 2.28
Expansion coefficient: 80.5 x 10e-7 per degree C
Oxides causing abnormal expansion effects: B2O3
++++++++++++++++++++++++++++++++++++++++++++++++++
+++ Modified glaze 2 with increased silica +++
++++++++++++++++++++++++++++++++++++++++++++++++++
Date: 06/11/98
Frit 3134 23.8 23.8%
Nepheline syenite 22.6 22.6%
Wollastonite 22.1 22.1%
Talc 2.2 2.2% Hazard!
EPK 18.6 18.6% Hazard!
Flint 10.7 10.7% Hazard!
-------- ------
100 100 %
Zircopax 12.2 12.2%
Copper carbonate 3 3 % Hazard!
Bentonite 2 2 % Hazard!
===========================
Chemical Analysis
===========================
Na2O 0.19 Al2O3 0.33 SiO2 2.56
K2O 0.03 B2O3 0.20 TiO2 0.00
MgO 0.07 Fe2O3 0.00
CaO 0.65 ZrO2 0.17
CuO 0.06
Alumina:Silica ratio is 1.00 : 7.84
Neutral:Acid ratio is 1.00 : 5.21
Alkali:Neutral:Acid ratio is 1.00 : 0.52 : 2.72
Expansion coefficient: 76.2 x 10e-7 per degree C
Oxides causing abnormal expansion effects: B2O3
John Post
rp1mrvl@moa.net
Sterling Heights, MI USA
Tom Buck on sun 14 jun 98
Kathy A: I wondered if others would respond, but since I've not seen one
here is my take on your problem:
Your recipe involves Nepheline Syenite and Gerstley Borate. The
former can lead to crawling in some conditions. The GB is an unreliable
ingredient because it exhibits a "moving target" in chemical composition.
Further, the recipe will yield a glass low in silica. The Seger Formula
is:
CaO 0.72 B2O3 0.21 SiO2 2.28
MgO 0.05 Al2O3 0.34
KNaO 0.23 Ratio = 6.7 Expansion= 7.3x10-6
A Cone 6 glaze is best if CaO is 0.7 max; if Al2O3 is 0.35 max; and SiO2
is at least 2.5.
I'd try this version of the recipe:
Addy's C6 Copper/Zirconium Glaze
31.0 Nepheline Syenite
20.0 Wollastonite
16.5 Gersley Borate
10.0 EPKaolin
11.0 Flint
11.5 Zircopax (or equal)
3.0 Copper carbonate basic
2.0 Bentonite
This raises the Ratio to 7.5 (means glossy on most bodies), and the
Expansion goes to 7.1x10-6. This may be enough change to halt the crawling
but careful application will still be needed, ie, do not make thick.
Good tests.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
On Tue, 9 Jun 1998, Kathy Addy wrote:
> ----------------------------Original message----------------------------
> The following Cone 6 electric glaze was a beautiful no-problem glaze first tim
> we tried it at the (now defunct) Potters Guild in Atlanta. The second batch a
> my own subsequent batch have exhibited problems of crawling. The glaze just
> seems to let go in spots regardless of how careful I am in surface preparation
> Can anyone out there suggest a reason this might happen?
>
> Nepheline syenite 31.11
> Wollastonite 22.22
> Gerstley Borate 17.78
> Zircopax 12.22
> Kaolin 11.11
> Silica 5.56
>
> Copper Carb 3.00
> Bentonite 2.00
> (I always add a squirt of pre-mix CMC too.)
>
> Grateful for your feedback.
>
> K.
>
Les Crimp on mon 15 jun 98
Hi K. -
I am sorry I can not help with the glaze problem, but I am interested in why
your Guild is now "defunct".
We have a Guild here in Parksville, B.C. (West coast Canada). Although ours
is running very well and we are now opening a gallery in conjunction with
our studio, it is very disconcerting to hear of a brother/sister guild that
did not make it.
Were there any salient reasons for the guild's demise??
Best regards,
Les Crimp in Nanoose Bay, B.C. in our lush green rainforest.
>----------------------------Original message----------------------------
>The following Cone 6 electric glaze was a beautiful no-problem glaze first time
>we tried it at the (now defunct) Potters Guild in Atlanta. The second
batch and
>my own subsequent batch have exhibited problems of crawling. The glaze just
>seems to let go in spots regardless of how careful I am in surface preparation.
>Can anyone out there suggest a reason this might happen?
>
> Nepheline syenite 31.11
> Wollastonite 22.22
> Gerstley Borate 17.78
> Zircopax 12.22
> Kaolin 11.11
> Silica 5.56
>
> Copper Carb 3.00
> Bentonite 2.00
> (I always add a squirt of pre-mix CMC too.)
>
>Grateful for your feedback.
>
>K.
>
>
Paul Lewing on tue 16 jun 98
Original message----------------------------
> >The following Cone 6 electric glaze was a beautiful no-problem glaze first ti
> >we tried it at the (now defunct) Potters Guild in Atlanta. The second
> batch and
> >my own subsequent batch have exhibited problems of crawling. The glaze just
> >seems to let go in spots regardless of how careful I am in surface preparatio
> >Can anyone out there suggest a reason this might happen?
> >
> > Nepheline syenite 31.11
> > Wollastonite 22.22
> > Gerstley Borate 17.78
> > Zircopax 12.22
> > Kaolin 11.11
> > Silica 5.56
> >
> > Copper Carb 3.00
> > Bentonite 2.00
> > (I always add a squirt of pre-mix CMC too.)
> >
> >Grateful for your feedback.
> >
> >K.
I can't see anything in your glaze recipe that would lead me to expect
crawling. But I had a similar problem with a couple of glazes, one a
comercial glaze, the other a scrap glaze. One day Louis Katz posted a
message about dealing with scrap glazes that suggested decanting the
water off them a couple of times to prevent crawling. And that fixed
it in both the scrap and the commercial glaze. I hope it works for
you. If it does, a better chemist than I will have to explain to you
why it does work.
Paul Lewing, Seattle
Catherine Kelly on mon 11 jun 01
I am requesting information on a problem that I have been having for quite
some time now. Without changing any of the glaze ingredients even using
the same drum from one day to the next the glaze will have very bad
crawling on the rims and the next day may have none. I have done so many
tests over the last year but to no avail. It is as if the crawling goes
into some form of remmission and then comes back again.
After doing tests such as thick glaze, soft bisque, residue from hands,
etc. etc. I am no closer, I am in fact more confused.
The ingredients used in the glaze are
Borax
Low Expansion Frit
Zinc Oxide
Zirconium Dioxide
Titanium Dioxide
Some help would be greatly appreciated.
Ababi on mon 11 jun 01
> Low Expansion Frit
> Zinc Oxide
> Zirconium Dioxide
> Titanium Dioxide
The way it looks, trying to be more carfull than my last answer, I see there
is not any clay. besides, I think this is the best recipe i ever saw! No
numbers! means? Put whatever you want and how much you want.
If you want an advise, please send the correct recipe. If it is a secret
recipe that your studio profits depend on it send it off list to someone you
trust or to a laboratory.
The next part is a joke(So don't kill me)
A cake
Flour
water
milk
Sodabicarbonate
eggs
NaCl
Sugar
Bye Bye
Ababi
----- Original Message -----
From: "Catherine Kelly"
To:
Sent: Monday, June 11, 2001 5:28 PM
Subject: Glaze crawling
> I am requesting information on a problem that I have been having for quite
> some time now. Without changing any of the glaze ingredients even using
> the same drum from one day to the next the glaze will have very bad
> crawling on the rims and the next day may have none. I have done so many
> tests over the last year but to no avail. It is as if the crawling goes
> into some form of remmission and then comes back again.
> After doing tests such as thick glaze, soft bisque, residue from hands,
> etc. etc. I am no closer, I am in fact more confused.
> The ingredients used in the glaze are
> Borax
> Low Expansion Frit
> Zinc Oxide
> Zirconium Dioxide
> Titanium Dioxide
>
> Some help would be greatly appreciated.
>
>
____________________________________________________________________________
__
> 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 thu 14 jun 01
Some glazes will tend to crawl if loaded and fired while still wet - trying
letting them dry completely before stacking.
If you need more help send me the recipe and perhaps I can reformulate to
make it more reliable - no clay in a recipe can make for real problems of
this kind.
RR
>I am requesting information on a problem that I have been having for quite
>some time now. Without changing any of the glaze ingredients even using
>the same drum from one day to the next the glaze will have very bad
>crawling on the rims and the next day may have none. I have done so many
>tests over the last year but to no avail. It is as if the crawling goes
>into some form of remmission and then comes back again.
>After doing tests such as thick glaze, soft bisque, residue from hands,
>etc. etc. I am no closer, I am in fact more confused.
>The ingredients used in the glaze are
>Borax
>Low Expansion Frit
>Zinc Oxide
>Zirconium Dioxide
>Titanium Dioxide
>
>Some help would be greatly appreciated.
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 thu 14 jun 01
Ababi requested I post this - It is because I needed to correct what was
said about a glaze problem. I sent a personal message explaining the
difference between crawling and expansion.
Ababi said - The expansion is too low too , means it must be too much crawling.
How to adjust what you have in the bucket?
Expansion has nothing to do with crawling but does have to do with wether
the clay and glaze fit well upon cooling together. If the expansion is too
low you can get dunting and shivering because the glaze is not contracting
(during cooling) enough compared to the contraction of the clay body.
Crawling has to do with raw glaze not being able to dry on the pot without
cracking so much that the glaze does not cover the ware in a complete way.
Most glazes do some cracking during the drying and sintering but if the
cracking is too much and/or the glaze is too stiff the bare spots remain.
I have also commented on a possible solution to this problem in another
post today.
RR
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
Snail Scott on fri 15 jun 01
At 01:37 PM 6/15/01 -0400, you wrote:
>I have never experienced glaze crawling, and I hope I never do. But, I
>apply all my glazes by brush, generally 3 coats. Is this why the glaze
>doesn't crawl, for me?
>
>Marianne Lombardo
Crawling is often caused by high-shrinkage
glazes (lots of clay in them, usually), dusty
bisque, and too-thick coatings. Slip glazes
often crawl if applied to bisque, for instance.
A tendency to crawl is often indicated by
cracking in the dry, unfired glaze coat.
Crawling due to a dusty surface usually isn't
visible before firing unless it's really severe,
but it can often be diagnosed afterward by the
way large areas pulled away, not just patches.
Excess thickness can be explained by analogy:
A thin layer that cracks tends to do so in small
pieces, with small gaps between them, like a
shallow mud puddle on pavement, or a thin coat
of crackle glaze in raku. A deep mud pit or a
thick coat of raku crackle will crack in larger
chunks, with larger cracks between them. Small
cracks in dry glaze coats will usually heal
themselves during the melt, but larger ones
may not be bridged by melting glaze, and surface
tension will tend to cause the edges to 'ball
up' rather than spreading out.
Double-dipping can induce crawling too, since
the second layer re-wets the first layer, and
can cause it to expand away from the clay
underneath. And, since it's thicker in the
doubled areas, this can contribute to the
problem. You occasionally see work where both
glazes are fine, singly, but have crawled where
they overlap.
There might be less crawling of brushed glazes
since the shrinkage of the wet glaze would occur
in layers, not all at once as with dipping. It
might also be that you've never encountered one
of the high-shrinkage recipes, but the notion
that brushing makes a difference might bear closer
consideration. (I don't get much crawling either,
even though I use a lot of high-clay glazes, and
I brush all my glazes, too.)
-Snail
Clay Coordinator on fri 15 jun 01
I don't now but you ight me having some proems with the borax. In which case
it might involve the firing speed.
I had some problems with Pete's Red Glaze (12% Gerstley Borate). If I would
fire it too fast through 500 - 1000 degree F it would butterfly roll. This
had to do with the thickness ofthe glaze and the firing speed. Gerstley has
a lot of water to burn off.
Your borax may be doing the same thing. If I remember correctly it frothes
quite a bit.
Something to consider,
Thanks,
John Britt
Penland Clay
>I am requesting information on a problem that I have been having for quite
>some time now. Without changing any of the glaze ingredients even using
>the same drum from one day to the next the glaze will have very bad
>crawling on the rims and the next day may have none. I have done so many
>tests over the last year but to no avail. It is as if the crawling goes
>into some form of remmission and then comes back again.
>After doing tests such as thick glaze, soft bisque, residue from hands,
>etc. etc. I am no closer, I am in fact more confused.
>The ingredients used in the glaze are
>Borax
>Low Expansion Frit
>Zinc Oxide
>Zirconium Dioxide
>Titanium Dioxide
>
>Some help would be greatly appreciated.
Paul Taylor on fri 15 jun 01
Dear Catherine
I have also had the same problem.
I have not bothered to find out exactly why but it is either the pots
were left too long before biscuiting or too long before glaze firing or
both.
I notice that the pots left too long before biscuit go yellow I guess
sulphur and may be other salts.
Any biscuit ware that lazzes around gets covered in dust, which is a
mixture of clay , turf ash and what ever. I do not understand why blowing it
off with the compressor does not do the job. I think a non clay type dust
gets smeared into the pores and that causes crawling or a layer of salt
fluxes the body layer too much and that increases the effect of the surface
tension of the glaze so a viscose glaze starts to crawl. you can see this by
looking at a drop of water put on a dry surface and compare it to one on an
oiled surface On the oiled surface the surface tension seems more because
there is no drag from the base so the droplet can gather up more.
My glazes do tend to crawl a little because I design them to be thick and
translucent on the pot . The esthetic that demands no pin holes and no
crawling is ok for Han emperors who owned potterys and for modern industry
which sets our esthetic standards by what it does best. Within reason I try
not to get hung up about it because it is the price you pay for a better
surface quality than the thin and shiny offered by industry . I sell
slightly crawled pots as seconds to grateful poor people like myself who are
not so fussy. The idealists pay for their Ideals and buy firsts - we are all
happy.
Come the time when you suspect a pot is going to crawl (by murphy's law)
a good trick is to have a glaze that looks the same as the glaze you are
using or clear but fires less viscose and probably a little runny. You spray
a micro layer on top of the glaze. Of course I only do this with large bowls
and large crocks with lids. It's not worth it on little pots.
I also get crawling if my glaze is too flocculated. When the glaze dries
out small cracks appear and some do not heal over . Its always a delicate
balance between having a glaze that goes on a dream and crawls and a
defloculated glaze of the same consistency that runs all over the pot.
So when you mix the glaze up fresh your glaze gets micro cracks and a week
later it has defloculated naturally and after taking some water off the
glaze shrinks less , no cracking and therefor no crawling. However your
glaze has no clay in it. I could speculate that such glazes were also
subject to defloculation but because they are so loose and powdery they have
no elasticity when drying and tend to crack very easily - but here I am
guessing.
Also for viscose glazes it can be a matter of a few of thousandths between
a crawling glaze and a perfect surface.
Another thing is that while on a smooth body a glaze may crawl it may also
crawl on a dusty surface you may have used a sponge on the rims at some time
but could not find the sponge the next time.
And yet another reason rims thrown on a monday can be a little thinner that
those thrown on a friday so when you glaze mondays pots the glaze does not
immediately soak into the pot and form a crust but stays a little wet and
air dries which for some reason is always more liable to crack. The weather
could at a push do that but I think that may be over speculative.
And ironically the opposite can be true. A thicker surface gives a thicker
glaze covering which puts it over the edge and the glaze starts to gather in
on its self and crawls but I doubt if this is your problem.
And to make you even more confused the chances are it is not one of these
faults causing the problem but a combination of a little of everything
making it difficult to pin down.
Other than that you could put a more efficient glaze on. Then get a
stamping machine that's makes the pots more even - because making sensual
pots by hand is so unproductive and risky :) -------------
By the way zinc oxide loves to crawl adding zircon makes matters worse -
again I do not know why - I expect your glaze looks great and changing the
glaze may spoil the other effects . The big however is ; could you make the
glaze less likely to crawl by re designing the glaze with a bit of clay in
it, so it gives a stronger and elastic dried surface. This is also
speculation on my behalf. Some others who deal with lots of different glazes
would know better than I just by looking at your glaze recipe - if it is
liable to crawl due to no clay or too much.
A good trick is to spray suspect pots putting the glaze on in layers this
sometimes helps
--
Regards Paul Taylor
> From: Catherine Kelly
> Reply-To: Ceramic Arts Discussion List
> Date: Mon, 11 Jun 2001 11:28:02 -0400
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Glaze crawling
>
> I am requesting information on a problem that I have been having for quite
> some time now. Without changing any of the glaze ingredients even using
> the same drum from one day to the next the glaze will have very bad
> crawling on the rims and the next day may have none. I have done so many
> tests over the last year but to no avail. It is as if the crawling goes
> into some form of remmission and then comes back again.
> After doing tests such as thick glaze, soft bisque, residue from hands,
> etc. etc. I am no closer, I am in fact more confused.
> The ingredients used in the glaze are
> Borax
> Low Expansion Frit
> Zinc Oxide
> Zirconium Dioxide
> Titanium Dioxide
>
> Some help would be greatly appreciated.
>
> ______________________________________________________________________________
> 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.
Marianne Lombardo on fri 15 jun 01
I have never experienced glaze crawling, and I hope I never do. But, I
apply all my glazes by brush, generally 3 coats. Is this why the glaze
doesn't crawl, for me?
Marianne Lombardo
Omemee, Ontario, Canada
email: mlombardo@nexicom.net
> A good trick is to spray suspect pots putting the glaze on in layers this
> sometimes helps
Snail Scott on sun 17 jun 01
This is a response to a private post to Lorri,
but it keeps bouncing, so I'm sending it to
the list:
At 07:32 AM 6/16/01 -0500, you wrote:
>Snail,
>...I was told that the "best" way to apply glazes is
>by dipping - that you can't get as nice of a finish
>by brushing...(why do you)...
Lorri-
It is true that a dipped surface is usually
quicker and more consistent than a brushed
surface. There are several reasons why a
person might brush glazes instead, though.
The work might be too large or awkwardly
shaped to fit the bucket, or the glaze might
only be wanted in certain areas or applied
in patterns.
Both of these reasons apply to my work. I
am a sculptor, not a potter. My work is
often too large to lift easily. Also, I
seldom want the same glaze all over a piece;
I prefer to add glaze just to specific
areas.
When brushing, you must be especially careful
to note the thickness of the application,
since it can vary quite a bit, and it's
easy to miss spots after the first coating.
The most common problem with brushed glazes
a too-thin application. When dipping, the
thickness is controlled by the porosity of
the bisque, eliminating that variable.
If dipping is suitable to the type of work
you do, I do recommend doing it that way.
Pouring can often substitute when a dipped
effect is desired, but isn't always a workable
or appropriate method. If not, it is possible
to get a good surface by brushing, but it
does take a little extra effort and attention.
(You can see some of my work at the SUCAWS
website. Not much glaze on that one, though;
just a little.)
-Snail
Snail Scott on sun 17 jun 01
>Date: Sat, 16 Jun 2001 08:36:59 -0700
>To: "Lorri"
>From: Snail Scott
>Subject: Re: Glaze crawling
>In-Reply-To: <005c01c0f660$799b7b60$775099d1@lorri>
>References:
<3.0.5.32.20010615182301.008428e0@mindspring.com>
>
>At 07:32 AM 6/16/01 -0500, you wrote:
>>Snail,
>>I enjoy your Clayart posts and thank you for the generous amount of
>>information you share. I have a question I hope you don't mind answering on
>>this brushing. I was told that the "best" way to apply glazes is by
>>dipping - that you can't get as nice of a finish by brushing...
>
>Lorri-
>
>It is true that a dipped surface is usually
>quicker and more consistent than a brushed
>surface. There are several reasons why a
>person might brush glazes instead, though.
>The work might be too large or awkwardly
>shaped to fit the bucket, or the glaze might
>only be wanted in certain areas or applied
>in patterns.
>
>Both of these reasons apply to my work. I
>am a sculptor, not a potter. My work is
>often too large to lift easily. Also, I
>seldom want the same glaze all over a piece;
>I prefer to add glaze just to specific
>areas.
>
>When brushing, you must be especially careful
>to note the thickness of the application,
>since it can vary quite a bit, and it's
>easy to miss spots after the first coating.
>The most common problem with brushed glazes
>a too-thin application. When dipping, the
>thickness is controlled by the porosity of
>the bisque, eliminating that variable.
>
>If dipping is suitable to the type of work
>you do, I do recommend doing it that way. If
>not, it is possible to get a good surface
>by brushing, but it does take a little extra
>effort and attention.
>
>(You can see some of my work at the SUCAWS
>website. Not much glaze on that one, though;
>just a little.)
> -Snail
Catherine Kelly on thu 16 aug 01
Hi There!
I have a recurring problem with my glaze. The rims of some pots "Crawl".
The strange thing is...using the same drum of glaze from one day to the
next I can have it one day and not the next. It seems to happen on certain
types of pots but at the same time may not be limited to them. To be
honest I have tried to solve this problem for 1 1/2 years and am no
closer. It always crawls on the piece of pot where glaze is that bit
thicker ( where it has overlapped ). But another day I could apply a really
thick glaze and it will not crawl. It has me baffled. I am including my
glaze formula in the hope that somebody out there can help..maybe even re-
formulate it for me. I use earthenware clay.
25kg Borax
10.01kg Low Expansion Frit
4.95kg Zinc Oxide
3.96kg Zirconium Silicate
0.82kg Titanium Dioxide
Martin Howard on fri 17 aug 01
Catherine, as one who uses earthenware, I can perhaps help you a little.
Using David Hewitt's Glaze Workbook, your Glaze Coefficient of Expansion,
English and Turner, comes out at 5.6. I use 6.31. So you are rather low, IF
you are using the same clay as I do.
I use Standard Red Earthenware from Valentine Clays in Staffordshire,
England. I doubt if you use that one. But get the coefficient of expansion
of your clay and reduce it by between 5 and 10 percent. Your glaze COE
should come to that figure to stop crawling or crazing, IMHE.
Also your Al2O3 to SiO2 should be between 1/5 and 1/10. Yours comes out at
1/11.9.
A further point is that the B2O3 comes out at .418 to SiO2 at 1.366. The
proportion normally should be 1/10 or thereabouts. You are nearly 1/3.
Your Basic Oxide to Acids is 1/1.37. It should be at least 1/2.5 for a
gloss. Higher if you are using cones 1 or 2.
I would suggest you get David's program, or a similar one, and reformulate
the glaze, using your own RMs. It can be quite fun adjusting the figures and
then trying it out. Of course, the chief player in this drama is your kiln!
My figures above may be wrong, because I have input the RMs which I can
obtain in the UK. They may differ from yours of the same name.
Another problem may be that where you overlap two glazes there is some
conflict.
The top one then crawls. I have that problem between the glazes I have
formulated for single firing, and that which I buy in for double firing.
If I use the first over the second there's a fight!!
Need to mark the buckets very clearly:-)
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
Paul Taylor on fri 17 aug 01
Dear Catherine.
Crawling is a real hassle but I risk it for some glazes because they are
too nice and adjustments change the glaze too much.
So to solve your problem I am going o surmise that your glaze is too
beautiful to change. But you may have to make some small changes . As is my
habit I shall try to explain my thinking as I go along.
Firstly there is no clay in your glaze and secondly one of the major
constituents of the glaze is a soluble salt BORAX. both can cause problems
on there own - together they can gang up on you.
The trouble with not having any clay in the glaze is that means the glaze
has little give (elasticity) when it dries out on the pot. there is a
balance with the dried strength of the glaze and its shrinkage before
firing . so if you have no clay in the glaze what happens is that the minute
shrinkage in the glaze (with out clay) fractures the surface of the dried
glaze and although that shrinkage is as small as you can get in a glaze,
that glaze is so brittle that cracks appear especially where one bit of
glaze meets another . If you are lucky the micro cracks will heal over in
the firing but that depends on the viscosity of the fired glaze and the
relative thickness of the glaze . The viscosity is a part of the surface
tension of the glaze. too high a viscosity and the glaze prefers to stick to
itself than the pot especially if the glaze is on thick -then you get
crawling.
If the glaze hangs around in the bucket the particles get mixed smaller
so the glaze shrinks a little more on drying and it cracks a little more so
the crawling starts or gets worse. If you over grind a glaze with too little
clay in it it will crawl like mad.
The irony is that a glaze with too much clay in it will also crawl
because the shrinkage of the drying glaze is more than the elasticity of the
clay in it. Not helped of course by the fact that high clay glazes have a
lot of alumina in which is viscose and that does not help crawling either.
I do not think viscosity is your problem, but I could be wrong. As your
water evaporates off , or a large pot sucks more water in than it is due, or
your biscuit pots are fired a bit lower, your glaze melter is disappearing
into the air and/or the pots; which means your glaze does not melt as much
and that raises the viscosity . Also underfired glazes do not heal over in
the firing and are more viscoes or behave that way . This can induce
crawling -- but with and zink and titanium any thing can happen so I dare
not speculate too much - I cloud be wrong here ??.
What are you going to do ??
In order of merit I would make sure that you do not change the amount of
water in your glaze after you have made it up, by keeping a lid on the
bucket. However it is very difficult to control a glaze with soluble salts
in, since the solubility increases with time even if you keep a lid on. you
may be losing borax to the water the longer you keep the glaze, which
disappears into the pot, or forms a salt on the surface of the glaze. The
mind boggles at the changes that soluble salts bring to a glaze over time
which is why potters try to avoid them like the plague ---- some potters
manage so why cant you . I heard spraying and trying to mix up the glaze
fresh every time helps. but defiantly keep the lid on the bucket and
remember that every time you change the thickness of the slop you change the
glaze recipe.
If that does not work you could add one of those glaze additives that
increase suspension and the elasticity of the glaze . Your supplier will
have the most modern. The soluble salts in you glaze may not agree with the
additive but its worth a try . Do not use too much by the sound of it you
only need a small correction.
So there is always bentonite. It's more of a slime than a clay and if your
glaze is only just misbehaving only one percent might do it, but you could
go to five percent. Put the bentonite in in the powder stage. If not you are
in for a fun time mixing it in and if it does work you wont be sure what
proportions you have put in - that's the sort of thing I do.
You do realize that your glaze is a boron glass with not a lot of silica
the more I look at it the more I do not understand it so I will leave
changing the actual chemistry of the glaze to someone expert with boron
glazes but try my ideas before you start playing with the recipe.
Make sure your biscuit kiln is firing evenly and high or low enough -
although I suspect too high a biscuit will prevent the glaze keying into the
pot and keep the glaze from drying quickly which could make matters worse -
too low a biskit and you are loosing the glaze in the pot - again a
balancing act.
By the way I think the description "glazes chemistry" is not a good
description for designing glazes and putting them on a pot "Glaze Juggling"
would be more accurate.
Regards from Paul Taylor
http://www.anu.ie/westportpottery
Alchemy is the proof that economics is not a science.
> From: Catherine Kelly
> Reply-To: Ceramic Arts Discussion List
> Date: Thu, 16 Aug 2001 16:25:02 -0400
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Glaze Crawling
>
> Hi There!
> I have a recurring problem with my glaze. The rims of some pots "Crawl".
> The strange thing is...using the same drum of glaze from one day to the
> next I can have it one day and not the next. It seems to happen on certain
> types of pots but at the same time may not be limited to them. To be
> honest I have tried to solve this problem for 1 1/2 years and am no
> closer. It always crawls on the piece of pot where glaze is that bit
> thicker ( where it has overlapped ). But another day I could apply a really
> thick glaze and it will not crawl. It has me baffled. I am including my
> glaze formula in the hope that somebody out there can help..maybe even re-
> formulate it for me. I use earthenware clay.
>
> 25kg Borax
> 10.01kg Low Expansion Frit
> 4.95kg Zinc Oxide
> 3.96kg Zirconium Silicate
> 0.82kg Titanium Dioxide
David Hewitt on fri 17 aug 01
Zinc oxide is a known culprit for crawling as it causes pre-firing
shrinkage and this glaze is particularly high in this oxide.
Do you see any evidence of such shrinkage?
David
In message , Catherine Kelly writes
>Hi There!
>I have a recurring problem with my glaze. The rims of some pots "Crawl".
>The strange thing is...using the same drum of glaze from one day to the
>next I can have it one day and not the next. It seems to happen on certa=
>in
>types of pots but at the same time may not be limited to them. To be
>honest I have tried to solve this problem for 1 1/2 years and am no
>closer. It always crawls on the piece of pot where glaze is that bit
>thicker ( where it has overlapped ). But another day I could apply a real=
>ly
>thick glaze and it will not crawl. It has me baffled. I am including my
>glaze formula in the hope that somebody out there can help..maybe even re=
>-
>formulate it for me. I use earthenware clay.
>
>25kg Borax
>10.01kg Low Expansion Frit
>4.95kg Zinc Oxide
>3.96kg Zirconium Silicate
>0.82kg Titanium Dioxide
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Web site http://www.dhpot.demon.co.uk
Conrad Krebs on tue 22 jun 04
Hello, I am applying low-fire clear matte glaze (Laguna, cone 06) to low-
fire bisque (Laguna, cone 06). Most recently I fired a piece to 1820 F in
an effort to reduce the shine. I allowed it to soaked at that temp for 1
minute. However, I had previously been firing the same glaze up to only
1800 F and holding at that temp for 2 minutes. I stopped doing that when I
thought I might be getting pinholing from underfiring of the glaze. Here's
my question. I am spraying the glaze onto the piece. Up to this point I
have avoided using an opacifier because from previous experience I thought
that it muddied the glaze color (a Mason stain mixed into the glaze base).
However, as a result I have been applying thicker and thicker coats of
glaze in an attempt to prevent the white clay body from showing through the
fired glaze. I think that I finally applied a coat that was so thick that
it resulted in crawling of the glaze. Am I missing something here? Or do I
just have to bite the bullet and use an opacifier so that I can apply a
glaze coat of a reasonable thickness? Thanks.
Conrad
Snail Scott on wed 23 jun 04
At 03:51 PM 6/22/2004 -0400, you wrote:
>Hello, I am applying low-fire clear matte glaze (Laguna, cone 06) to low-
>fire bisque...with mason stains...
>I have been applying thicker and thicker coats of
>glaze in an attempt to prevent the white clay body from showing through the
>fired glaze...
Umm...why are you starting with a clear glaze if you want
opaque coverage? If you are committed to modifying commercially-
made glazes, why not start with one that's 'in the ballpark';
i.e. an opaque matte?
The other easy way to conceal the color of a clay body is
to use a slip or engobe under the glaze. An underglaze of
contrasting color can give interesting effects, while one
of similar color can regularize the appearance of a glaze.
Variously-colored underglazes on the same piece can also give
subtle modulation to the final effect of a single colored glaze.
-Snail Scott
Edwardsville, Illinois, USA, Earth
Joyce Lee on wed 23 jun 04
ok
----- Original Message -----
From: "Conrad Krebs"
To:
Sent: Tuesday, June 22, 2004 12:51 PM
Subject: glaze crawling
> Hello, I am applying low-fire clear matte glaze (Laguna, cone 06) to low-
> fire bisque (Laguna, cone 06). Most recently I fired a piece to 1820 F in
> an effort to reduce the shine. I allowed it to soaked at that temp for 1
> minute. However, I had previously been firing the same glaze up to only
> 1800 F and holding at that temp for 2 minutes. I stopped doing that when I
> thought I might be getting pinholing from underfiring of the glaze. Here's
> my question. I am spraying the glaze onto the piece. Up to this point I
> have avoided using an opacifier because from previous experience I thought
> that it muddied the glaze color (a Mason stain mixed into the glaze base).
> However, as a result I have been applying thicker and thicker coats of
> glaze in an attempt to prevent the white clay body from showing through
the
> fired glaze. I think that I finally applied a coat that was so thick that
> it resulted in crawling of the glaze. Am I missing something here? Or do I
> just have to bite the bullet and use an opacifier so that I can apply a
> glaze coat of a reasonable thickness? Thanks.
>
> Conrad
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
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>
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melpots@pclink.com.
>
Barb Lund on sat 31 jul 10
I've been trying for a week to post his on the clay art board and somehow m=
y
server can't connect. Would you post this for me and let's see what kind o=
f
answers I might get.............
--------------------------------------------------
From:
> --------------------------------------------------
>>> I've been a full time studio potter since 1984. I fire a 90 cubic foot
>>> downdraft that I built. I live 'way out in the woods and fire with
>>> propane
>>> Much of my ware has a cobalt slip that I apply with a sponge and either
>>> scraffiti through or use with stencils. I use a clear glaze over it
>>> all. It's worked well for 20+ ears. Just recently(within the last 2 or
>>> 3 years) the glaze has stated to crawl off the cobalt. It's not just th=
e
>>> oxide, I mix it with a white slip. I doesn't crawl off the green slip o=
r
>>> the white.
>>> I have tried everything I or any potter I have talked to can think of
>>> and it still looks like it has leprosy.
>>> I mixed my glaze with gum in varying amounts, I mixed the slip with les=
s
>>> cobalt oxide, I tried cobalt carb,I found some "old" cobalt,(bought 10
>>> years ago) I used an entirely different glaze recipe,I fired slower,
>>> faster, to cone 6 instead of 9. If anything it's getting
>>> worse........oh, and it works fine in the electric kiln .ARGH!!
>>> Any help would be appreciated!!
>>> Susan for Sweetwater Pottery
>>> www.SweetwaterPottery.biz
>>>
>>>
>>>
>
------ End of Forwarded Message
Ron Roy on sun 1 aug 10
Hi Barb,
Send me the glaze and slip recipe and I'll see if changing the
materials will help.
RR
Quoting Barb Lund :
> I've been trying for a week to post his on the clay art board and somehow=
my
> server can't connect. Would you post this for me and let's see what kind=
of
> answers I might get.............
>
> --------------------------------------------------
> From:
>> --------------------------------------------------
>>>> I've been a full time studio potter since 1984. I fire a 90 cubic foot
>>>> downdraft that I built. I live 'way out in the woods and fire with
>>>> propane
>>>> Much of my ware has a cobalt slip that I apply with a sponge and eithe=
r
>>>> scraffiti through or use with stencils. I use a clear glaze over it
>>>> all. It's worked well for 20+ ears. Just recently(within the last 2 o=
r
>>>> 3 years) the glaze has stated to crawl off the cobalt. It's not just t=
he
>>>> oxide, I mix it with a white slip. I doesn't crawl off the green slip =
or
>>>> the white.
>>>> I have tried everything I or any potter I have talked to can think of
>>>> and it still looks like it has leprosy.
>>>> I mixed my glaze with gum in varying amounts, I mixed the slip with le=
ss
>>>> cobalt oxide, I tried cobalt carb,I found some "old" cobalt,(bought 10
>>>> years ago) I used an entirely different glaze recipe,I fired slower,
>>>> faster, to cone 6 instead of 9. If anything it's getting
>>>> worse........oh, and it works fine in the electric kiln .ARGH!!
>>>> Any help would be appreciated!!
>>>> Susan for Sweetwater Pottery
>>>> www.SweetwaterPottery.biz
>>>>
>>>>
>>>>
>>
>
>
> ------ End of Forwarded Message
>
Louis Katz on tue 3 aug 10
If your glaze is low in clay the gum you are using could help. But dusty
glazes are more prone to trouble in my experience. Oddly glazes high in c=
=3D
lay
are also prone to trouble.
It could be that your slip is too vitreous. I would think that if you ton=
=3D
gue
sticks to it or if a drop of water place on it is quickly absorbed this i=
=3D
s
not the case, anyways if this is true, gum in the glaze solves the proble=
=3D
m.
With all the rain down here and elsewhere this summer, I wonder if you co=
=3D
uld
possibly be in a drought. Really hard water can cause crawling in edgy
glazes, and this shows up most notably during droughts. If you are in a
drought try a batch with distilled water and see if it helps. If it is
normally a good working glaze and you use epsom salts or some other
flocculant try eliminating the flocculant or cutting WAY back.
We had a big run of crawling down here during a drought in the 90's. I
started using water from my dehumidifier for glazes. This helped a lot. T=
=3D
he
problem disappeared when we slowed down the start of our firings below 25=
=3D
0
degrees. The steam escaping quickly seemed to be the big culprit.
I currently have a crawling glaze. Its 50 arroyo slip (from Laguna) and 5=
=3D
0
Neph sy. and called Arroyo Kaki. While arroyo slip seems more like a silt=
=3D
,
the glaze coat has "too much shrinkage" I may have to calcine some of the=
=3D
arroyo slip and adjust the quantities. I am firing a board of cups with i=
=3D
t
unrevised to see how I feel about the crawls. For my work they could be O=
=3D
K.
In stead of changing the glaze I may start applying it green on leather h=
=3D
ard
clay.
Good luck, I would take Ron Roy up on his offer, skilled reformulating ca=
=3D
n
often result in a glaze with far superior working properties.
Bill Merrill on sat 21 apr 12
Crawling can be caused by applying glaze over a dusty surface on bisque
ware.
Crawling may happen when high clay glazes shrink too much in the wet to
dry stage. Substitute some of the raw clay with calcined clay.
High Zinc glazes have had a tendency to crawl , but most of the Zinc
purchased today is already calcined ( ask your supplier if it is
calcined or not. Seattle pottery Supply zinc is calcined)
Magnesium carbonate has a very high wet to dry shrinkage rate and will
crawl going from wet to dry. A typical "Crawl" surface glaze would be
(at cone 10) 65% Spar and 35% magnesium carbonate.
Robert Sperry's glaze was 50% Spar and 50% Magnesium carbonate. Fluxes
may be added and the ratios changed to create very dry to softened crawl
surfaces, along with merely changing the spar/magnesium carb ratios
Using a simple line blend.
Letting a glaze dry and then pouring or dipping the glaze over the
original coat of glaze.
These are just a few things about crawling...there are more, but these
are common. I deliberately use a MC/Spar mix over some of the glazes I
use on large platters.
Bill Merrill
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