Wanda Holmes on fri 6 sep 02
I am trying to develop a stable alkaline glaze for cone 6 oxidation.
The following glaze gives a beautiful clear glass with exactly the color
I want with 4% copper carb, but it crazes like crazy immediately upon
removal from the kiln.
Frit 3110 20
EPK 10
Silica 27
Frit 3289 34
Lithium carb 4
GlazeChem gives this glaze a COE of 73.5. I've been adding silica to
bring down the COE. I've gotten the COE down to as low as 66.7 although
the glaze has now lost many of its original and desirable properties of
color and clarity. It has not, however, lost the crazing property.
GlazeChem gives John & Ron's calcium semi-matte a COE of 72.6. I have
absolutely no problems with it, on the same claybody fired exactly the
same way.
Why does one glaze with a higher COE work just fine while another with a
much lower COE craze like the dickens? What am I missing?
Wanda
Autumn Downey on sat 7 sep 02
John,
You may hear from David Hewitt with other/newer? info, but this is what he
sent to me a few years ago in a posting. (And my mailbox system was good
enough to allow me to find it again!)
>Mayer & Havas give the following figures in % Wt. Cubic x10^-7/oC. To
>convert to Linear coefficients, divide by 3.
>Cr2O3 5.1
>CoO 4.4
>Fe2O3 4.0
>NiO 4.0
>MnO 2.2
>CuO 2.2
>SnO2 2.0
>I think the GlazeChem program includes a value for every oxide.
>I always like to include the colouring oxides when calculating the
>expansion.
>David
>
Autumn Downey
At 09:32 PM 2002-09-07 -0400, you wrote:
>John,
>
>I am interested in finding a list of colorants exp/cont. Does this exist?
>
>Thanks, John Britt
>
>___________________________________________________________________________
___
Autumn Downey on sat 7 sep 02
Hello Wanda,
Not a guru, but am interested in glazes. I couldn't find Frit 3289 in my
Insight materials though, to see what the analysis is.
I'm not sure what R&J will tell you - but maybe if you could use less
lithium - and get it from spodumene, it might help. I don't know if
partial use of strontium would be help or not. It's supposed to be
somewhat like lithium, but might not produce the turquoise??
Am cashing in on your question to ask a few of my own! Your last question
about some glazes not crazing, even with a higher COE than "crazers" is
something I've noticed too and wondered about. I wondered if there was
more rigidity to some glazes than others and that depended on the behaviour
of the oxides involved. Sometimes some colourants seem to improve an
otherwise crazing glaze? Glazes that are almost glass (with no opacifiers)
often seem to very hard to fit.
On that point, maybe 1 or 2% zircopax or tin would also help without
affecting clarity.
Anyway, will be watching for the responses you get!
Autumn Downey
Yellowknife, NWT
At 11:26 PM 2002-09-06 -0500, you wrote:
>I am trying to develop a stable alkaline glaze for cone 6 oxidation.
>The following glaze gives a beautiful clear glass with exactly the color
>I want with 4% copper carb, but it crazes like crazy immediately upon
>removal from the kiln.
>
>Frit 3110 20
>EPK 10
>Silica 27
>Frit 3289 34
>Lithium carb 4
>
>GlazeChem gives this glaze a COE of 73.5. I've been adding silica to
>bring down the COE. I've gotten the COE down to as low as 66.7 although
>the glaze has now lost many of its original and desirable properties of
>color and clarity. It has not, however, lost the crazing property.
>
>GlazeChem gives John & Ron's calcium semi-matte a COE of 72.6. I have
>absolutely no problems with it, on the same claybody fired exactly the
>same way.
>
>Why does one glaze with a higher COE work just fine while another with a
>much lower COE craze like the dickens? What am I missing?
>
>Wanda
>
>___________________________________________________________________________
___
>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.
>
>
Lily Krakowski on sat 7 sep 02
Unfortunately--and I know nothing of your glaze's problems, as I do not have
my frit chart here--there are many glazes that lose their beautiful color
when healed of certain defects, especially crazing. As I understand it the
crazing ITSELF affects how we SEE the color. And realize the craze is there
before you see it with the naked eye.
As someone who still is working on the problem of eating all possible
chocolate and not gaining a gram--I feel for you.
Wanda Holmes writes:
> I am trying to develop a stable alkaline glaze for cone 6 oxidation.
> The following glaze gives a beautiful clear glass with exactly the color
> I want with 4% copper carb, but it crazes like crazy immediately upon
> removal from the kiln.
>
> Frit 3110 20
> EPK 10
> Silica 27
> Frit 3289 34
> Lithium carb 4
>
> GlazeChem gives this glaze a COE of 73.5. I've been adding silica to
> bring down the COE. I've gotten the COE down to as low as 66.7 although
> the glaze has now lost many of its original and desirable properties of
> color and clarity. It has not, however, lost the crazing property.
>
> GlazeChem gives John & Ron's calcium semi-matte a COE of 72.6. I have
> absolutely no problems with it, on the same claybody fired exactly the
> same way.
>
> Why does one glaze with a higher COE work just fine while another with a
> much lower COE craze like the dickens? What am I missing?
>
> Wanda
>
> ______________________________________________________________________________
> 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.
Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389
Be of good courage....
John Hesselberth on sat 7 sep 02
Hi Wanda,
COE calculations are only reliable for glossy glazes. Once crystals
start to form all bets are off. So the number you calculated for our
calcium semimatte cannot be compared to the number for a glossy,
although you still might, in certain circumstances, be able to adjust a
particular semimatte glaze by looking at changes in the number.
The model used to calculate COE is a very simple one often called the
"rule of mixtures". It just is not sophisticated enough to account for
the large (relatively) volumetric changes that occur when a crystal
forms. When you add that to the fact that the level of crystallization
that occurs is affected by the cooling rate as well as the
composition--well it would take a very sophisticated mathematical model
to predict that.
While I have never observed it, it wouldn't surprise me to see crazing
in a semimatte glaze that is cooled rapidly (no crystals) and no crazing
in the same glaze cooled slowly (or perhaps more likely, vice versa).
Regards,
John
P.S. Getting a craze-free alkaline glaze at cone 6 may be an oxymoron.
I've had a few tries at it and have not succeeded. I'm not saying it
can't be done, but it will be a very small needle you are looking for in
the glaze haystack. You might have better luck if you can find a very
high expansion body. If anyone has a cvraxe-free alkaline glaze, I'll
bet it is Paul Lewing. Paul--is it possible???
On Saturday, September 7, 2002, at 12:26 AM, Wanda Holmes wrote:
> GlazeChem gives John & Ron's calcium semi-matte a COE of 72.6. I have
> absolutely no problems with it, on the same claybody fired exactly the
> same way.
>
> Why does one glaze with a higher COE work just fine while another with a
> much lower COE craze like the dickens? What am I missing?
Frog Pond Pottery
PO Box 88
Pocopson, PA 19366
Fax or phone: 610-388-1254
John Hesselberth on sat 7 sep 02
On Saturday, September 7, 2002, at 11:01 AM, Autumn Downey wrote:
> I wondered if there was
> more rigidity to some glazes than others and that depended on the
> behaviour
> of the oxides involved. Sometimes some colourants seem to improve an
> otherwise crazing glaze? Glazes that are almost glass (with no
> opacifiers)
> often seem to very hard to fit.
>
Hi Autumn
I think these things you speculate about definitely happen but I'd be a
little hard pressed to prove it. Moderate levels of boron seem to make
a glaze less prone to crazing even when the calculated expansion is
high--they seem like they are more "elastic". Some colorants also seem
to help.
Also your suggestion to use strontium is a good one. You can definitely
get copper-blues with some strontium-containing glazes.
Regards,
John
Frog Pond Pottery
PO Box 88
Pocopson, PA 19366
Fax or phone: 610-388-1254
John Britt on sat 7 sep 02
John,
I am interested in finding a list of colorants exp/cont. Does this exist?
Thanks, John Britt
iandol on sun 8 sep 02
Dear John Britt,
I think it is important for those people who wish to invoke COE as a =
tool in determining the properties of a glaze to know how this value is =
obtained. It is based on a summation of ascribed values of the =
proportions of the oxides which contribute to the glaze. This is a =
theoretical construct which, under some circumstances, give values which =
are approximately equal to the value of COE determined by experiment. =
Where it is determined by experiment, the value is only valid for the =
temperature range of the test for the specimen used at the time of =
testing. That being said, it can be a useful guide.
Since many oxides are not available in a form which can be tested, COE =
values we may obtain by using the facility in a glaze calculation =
program are guesses, not experimental values.
If you could obtain rods of fused colouring agents I am sure it would be =
possible construct the apparatus then measure COE values in the range of =
20=B0C to 500=B0C using hot air, a digital pyrometer and a micrometer.
Best regards,
Ivor Lewis
iandol on sun 8 sep 02
Dear Wanda Holmes,
It is always a puzzle trying to determine why things do not go as =
anticipated, according to the theory or the calculations.
I would make two points which I think are valid.
First is that you can always consider your current clay. Can this be =
changed or altered to alleviate the crazing problem.
The second is that there seem to be no notes in the literature =
suggesting those who intend designing glazes should take pre-emptive =
action to eliminate the problem before it arises.
Specific to your current situation. This seems to be a glaze with a very =
low maturity point. Perhaps the problem is due to immature clay at your =
chosen maturing temperature.
It will be interesting to know what the others propose.
Best regards,
Ivor Lewis. Redhill, South Australia
Wanda Holmes on sun 8 sep 02
John, thanks for the explanation. Regarding your suggestion to look for
a high expansion body, can you give me more specifics about what I
should be looking for? Is there a specific COE or COE range that I
should ask for? Wanda
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG] On
Behalf Of John Hesselberth
Sent: Saturday, September 07, 2002 11:48 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: COE - need help from glaze gurus
Hi Wanda,
COE calculations are only reliable for glossy glazes. Once crystals
start to form all bets are off. So the number you calculated for our
calcium semimatte cannot be compared to the number for a glossy,
although you still might, in certain circumstances, be able to adjust a
particular semimatte glaze by looking at changes in the number.
The model used to calculate COE is a very simple one often called the
"rule of mixtures". It just is not sophisticated enough to account for
the large (relatively) volumetric changes that occur when a crystal
forms. When you add that to the fact that the level of crystallization
that occurs is affected by the cooling rate as well as the
composition--well it would take a very sophisticated mathematical model
to predict that.
While I have never observed it, it wouldn't surprise me to see crazing
in a semimatte glaze that is cooled rapidly (no crystals) and no crazing
in the same glaze cooled slowly (or perhaps more likely, vice versa).
Regards,
John
P.S. Getting a craze-free alkaline glaze at cone 6 may be an oxymoron.
I've had a few tries at it and have not succeeded. I'm not saying it
can't be done, but it will be a very small needle you are looking for in
the glaze haystack. You might have better luck if you can find a very
high expansion body. If anyone has a cvraxe-free alkaline glaze, I'll
bet it is Paul Lewing. Paul--is it possible???
On Saturday, September 7, 2002, at 12:26 AM, Wanda Holmes wrote:
> GlazeChem gives John & Ron's calcium semi-matte a COE of 72.6. I have
> absolutely no problems with it, on the same claybody fired exactly the
> same way.
>
> Why does one glaze with a higher COE work just fine while another with
> a much lower COE craze like the dickens? What am I missing?
Frog Pond Pottery
PO Box 88
Pocopson, PA 19366
Fax or phone: 610-388-1254
________________________________________________________________________
______
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.
Wanda Holmes on sun 8 sep 02
Autumn, thanks for the suggestion about adding tin or zircopax. Frit
3289 is a barium frit with the following formula:
5.5 Na2O
27.4 BaO
12.4 B2O3
5.4 Al2O3
49.3 SiO2.
Wanda
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG] On
Behalf Of Autumn Downey
Sent: Saturday, September 07, 2002 10:02 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: COE - need help from glaze gurus
Hello Wanda,
Not a guru, but am interested in glazes. I couldn't find Frit 3289 in
my Insight materials though, to see what the analysis is.
I'm not sure what R&J will tell you - but maybe if you could use less
lithium - and get it from spodumene, it might help. I don't know if
partial use of strontium would be help or not. It's supposed to be
somewhat like lithium, but might not produce the turquoise??
Am cashing in on your question to ask a few of my own! Your last
question about some glazes not crazing, even with a higher COE than
"crazers" is something I've noticed too and wondered about. I wondered
if there was more rigidity to some glazes than others and that depended
on the behaviour of the oxides involved. Sometimes some colourants seem
to improve an otherwise crazing glaze? Glazes that are almost glass
(with no opacifiers) often seem to very hard to fit.
On that point, maybe 1 or 2% zircopax or tin would also help without
affecting clarity.
Anyway, will be watching for the responses you get!
Autumn Downey
Yellowknife, NWT
At 11:26 PM 2002-09-06 -0500, you wrote:
>I am trying to develop a stable alkaline glaze for cone 6 oxidation.
>The following glaze gives a beautiful clear glass with exactly the
>color I want with 4% copper carb, but it crazes like crazy immediately
>upon removal from the kiln.
>
>Frit 3110 20
>EPK 10
>Silica 27
>Frit 3289 34
>Lithium carb 4
>
>GlazeChem gives this glaze a COE of 73.5. I've been adding silica to
>bring down the COE. I've gotten the COE down to as low as 66.7
>although the glaze has now lost many of its original and desirable
>properties of color and clarity. It has not, however, lost the crazing
>property.
>
>GlazeChem gives John & Ron's calcium semi-matte a COE of 72.6. I have
>absolutely no problems with it, on the same claybody fired exactly the
>same way.
>
>Why does one glaze with a higher COE work just fine while another with
>a much lower COE craze like the dickens? What am I missing?
>
>Wanda
>
>_______________________________________________________________________
>____
___
>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.
>
>
________________________________________________________________________
______
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.
Wanda Holmes on sun 8 sep 02
Lily, if you ever solve that chocolate problem, be sure to let me
know.....w
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG] On
Behalf Of Lily Krakowski
Sent: Saturday, September 07, 2002 10:56 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: COE - need help from glaze gurus
Unfortunately--and I know nothing of your glaze's problems, as I do not
have my frit chart here--there are many glazes that lose their
beautiful color when healed of certain defects, especially crazing. As
I understand it the crazing ITSELF affects how we SEE the color. And
realize the craze is there before you see it with the naked eye.
As someone who still is working on the problem of eating all possible
chocolate and not gaining a gram--I feel for you.
David Hewitt on mon 9 sep 02
In considering any coefficient of expansion figures, calculated from a
recipe, I would say that they are at best only a guide. As john has said
they are meant to apply to a glaze where all ingredients have gone in to
the melt, i.e. a shiny glaze.
Also in considering these figures one must appreciate that different
ceramists have given different coefficients and with one or two the
calculation is a little mote complex. Appen is a particular example of
this. As autumn has pointed out, Mayer and Havas gives some figures for
colouring oxides. So also does Appen. English & Turner on the other hand
give none. Some people mix the coefficients from one ceramist's set with
another. To me this is a little dubious.
If readers of this thread wish to see the different ceramist's
coefficients and the way to use them in calculations, you can get this
from my web site:-
http://www.dhpot.demon.co.uk
Go to Pottery Techniques / Calculating Crazing.
My own preference is to use English & Turner and Appen
David
In message , Autumn Downey writes
>John,
>
>You may hear from David Hewitt with other/newer? info, but this is what h=
>e
>sent to me a few years ago in a posting. (And my mailbox system was good
>enough to allow me to find it again!)
>
>
>>Mayer & Havas give the following figures in % Wt. Cubic x10^-7/oC. To
>>convert to Linear coefficients, divide by 3.
>>Cr2O3 5.1
>>CoO 4.4
>>Fe2O3 4.0
>>NiO 4.0
>>MnO 2.2
>>CuO 2.2
>>SnO2 2.0
>>I think the GlazeChem program includes a value for every oxide.
>>I always like to include the colouring oxides when calculating the
>>expansion.
>>David
>>
>
>Autumn Downey
>
>
>At 09:32 PM 2002-09-07 -0400, you wrote:
>>John,
>>
>>I am interested in finding a list of colorants exp/cont. Does this exis=
>t?
>>
>>Thanks, John Britt
>>
>>________________________________________________________________________=
>___
>___
--
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
Wanda Holmes on mon 9 sep 02
Ivor, I made a mistake in my original posting. I left out an ingredient
in the recipe. The actual recipe is:
Frit 3110 20
EPK 10
Silica 27
Frit 3289 34
Whiting 9
Lithium carb 4.
With this correction, does your observation about maturation point still
hold? If so, what would you do to raise it?
Thanks for your help,
Wanda
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG] On
Behalf Of iandol
Sent: Saturday, September 07, 2002 1:30 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: COE - need help from glaze gurus
Dear Wanda Holmes,
It is always a puzzle trying to determine why things do not go as
anticipated, according to the theory or the calculations.
I would make two points which I think are valid.
First is that you can always consider your current clay. Can this be
changed or altered to alleviate the crazing problem.
The second is that there seem to be no notes in the literature
suggesting those who intend designing glazes should take pre-emptive
action to eliminate the problem before it arises.
Specific to your current situation. This seems to be a glaze with a very
low maturity point. Perhaps the problem is due to immature clay at your
chosen maturing temperature.
It will be interesting to know what the others propose.
Best regards,
Ivor Lewis. Redhill, South Australia
________________________________________________________________________
______
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.
iandol on tue 10 sep 02
Looking at what I wrote to you, yes, I do stand by that statement.
Even with the additional input about the missing ingredient I think
this is a glaze which will melt at a low temperature. With those
fritted fluxes, one being an Alkali borate and the other a Barium
borate, it seems like an earthen ware glaze for something like cone
04.
Another thing which disturbs me about this and similar mixtures is the
degree to which the refractory components; Silica, Whiting and Kaolin,
will dissolve. They need either time or heat to accomplish this. If
they do not go into solution then the glaze will be immature and may
be prone to crazing.
Definitely an interesting quandary.
Best regards,
Ivor Lewis
----- Original Message -----
From: "Wanda Holmes"
To: "'Ceramic Arts Discussion List'"
Cc: "'iandol'"
Sent: Monday, 9 September 2002 11:34
Subject: RE: COE - need help from glaze gurus
> Ivor, I made a mistake in my original posting. I left out an
ingredient
> in the recipe. The actual recipe is:
> Frit 3110 20
> EPK 10
> Silica 27
> Frit 3289 34
> Whiting 9
> Lithium carb 4.
>
> With this correction, does your observation about maturation point
still
> hold? If so, what would you do to raise it?
>
> Thanks for your help,
> Wanda
>
> -----Original Message-----
> From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]
On
> Behalf Of iandol
> Sent: Saturday, September 07, 2002 1:30 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: COE - need help from glaze gurus
>
>
> Dear Wanda Holmes,
>
> It is always a puzzle trying to determine why things do not go as
> anticipated, according to the theory or the calculations.
>
> I would make two points which I think are valid.
>
> First is that you can always consider your current clay. Can this be
> changed or altered to alleviate the crazing problem.
>
> The second is that there seem to be no notes in the literature
> suggesting those who intend designing glazes should take pre-emptive
> action to eliminate the problem before it arises.
>
> Specific to your current situation. This seems to be a glaze with a
very
> low maturity point. Perhaps the problem is due to immature clay at
your
> chosen maturing temperature.
>
> It will be interesting to know what the others propose.
>
> Best regards,
>
> Ivor Lewis. Redhill, South Australia
>
>
______________________________________________________________________
__
> ______
> 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 12 sep 02
Hi Wanda,
This must have gotten by me when I was away - anyway - anything below 7.0
COE has a good chance of not crazing on many bodies as illustrated in
chapter 5 in our book. What could be the problem in this case is the
accuracy of the materials definitions in your program - send me the other
recipe and I will check them out for you.
If you want to know the COE of any clay body use the glazes in Mastering
Glazes - you will certainly get a better picture of which bodies will help
in this situation.
Any way send me the other recipe - don't hold you breath about this -
potters (as someone else has pointed out) have been trying to solve this
one for centuries. Perhaps changing to a clay body with a higher COE may be
the way to go. Ask you clay supplier if they have any COE info on their
clays.
By the way - the boron in the glaze below is only at 5.2 percent so that
may be worth while - to increase that.
I have recalculated the recipe below adding more boron using frit 3134 -
keep in mind silica lowers expansion - the more frit in the body the faster
the melt - so it means you can get more silica in. The expansion is lowered
but not a lot.
By the way the recipe below only adds to 95 - it that right?
F3110 - 15.0
F 3289 - 27.0
F 3134 - 15.0
Lith Carb - 2.0
EPK - 13.0
Silica - 28.0
Total - 100.0
Ball clay would work better in this - I'm sure it's going to deflocc - let
me know what kinds of ball clay you can get.
RR
>Wanda Holmes writes:
>
>> I am trying to develop a stable alkaline glaze for cone 6 oxidation.
>> The following glaze gives a beautiful clear glass with exactly the color
>> I want with 4% copper carb, but it crazes like crazy immediately upon
>> removal from the kiln.
>>
>> Frit 3110 20
>> EPK 10
>> Silica 27
>> Frit 3289 34
>> Lithium carb 4
>>
>> GlazeChem gives this glaze a COE of 73.5. I've been adding silica to
>> bring down the COE. I've gotten the COE down to as low as 66.7 although
>> the glaze has now lost many of its original and desirable properties of
>> color and clarity. It has not, however, lost the crazing property.
>>
>> GlazeChem gives John & Ron's calcium semi-matte a COE of 72.6. I have
>> absolutely no problems with it, on the same claybody fired exactly the
>> same way.
>>
>> Why does one glaze with a higher COE work just fine while another with a
>> much lower COE craze like the dickens? What am I missing?
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on thu 12 sep 02
Hi John - there is a list in the back of the Hamer book which gives
relative expansion rates of most oxides we use.
I hear some saying do not mix expansion rates from different lists - that
is right but you can deduce relative expansion by comparing - for instance
-
Say CuO falls between Zinc at 7 and MgO at 4.0 (I'm making these up by the
way) then we can assume CuO is about 5.2 - accurate enough because so
little copper is usually used. Some lists have some of each so it is a work
around.
In fact Hamer says CuO is the same as MnO - big clue!
After that all one needs to do is construct an experiment to see if copper
increases expansion or lowers it in a glaze (glossy) with an expansion of
say 5.2. If it does not work then rethink.
There have been comments that some colours seem to affect expansion in ways
we cannot account for - there needs to be some work done in this area - not
rocket science to find out some useful information.
RR
>John,
>I am interested in finding a list of colorants exp/cont. Does this exist?
>
>Thanks, John Britt
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on fri 13 sep 02
Just a few points of clarification,
The calculated expansions do not take into account the range of temperature
- nor do they come close to actual measurements - in any way - using the
values we use at the moment.
Where calculated expansion of glossy glazes shines is in predicting which
way your are moving the expansion/contraction of a glaze when fixing fit.
Take a look at the chart of the glazes on page 71 in Mastering Cone 6
Glazes. Those glazes were designed using calculating software - notice how
even the gaps are between the glazes. I was surprised and delighted at the
accuracy.
It is better than a useful guide - given the accuracy of materials
definitions - it is a reliable guide in the hands of those willing to learn
the few exceptions and when they apply.
RR
>I think it is important for those people who wish to invoke COE as a tool
>in determining the properties of a glaze to know how this value is
>obtained. It is based on a summation of ascribed values of the proportions
>of the oxides which contribute to the glaze. This is a theoretical
>construct which, under some circumstances, give values which are
>approximately equal to the value of COE determined by experiment. Where it
>is determined by experiment, the value is only valid for the temperature
>range of the test for the specimen used at the time of testing. That being
>said, it can be a useful guide.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Wanda Holmes on fri 13 sep 02
Ron, thanks for your response and your help. I made a mistake when I
pasted the recipe into my original post. It should include 9 whiting
also, for a total of 104 (the lithium carb is in my 'also add' column,
hence the odd number).
I'm not sure I understand your reference to using the glazes in
Mastering Glazes to know the COE of my clay body. Can you elaborate -
I'm missing something.
Regarding ball clay, I have OM#4 on hand. Would that work?
My last test recipe was:
Frit 3110 16
EPK 10
Silica 33
Frit 3289 29
Whiting 8
Lithium carbonate 4
Na2O 0.24
K2O 0.02
MgO 0.00
CaO 0.35
Li2O 0.20
BaO 0.19
Al2O3 0.21
B2O3 0.21
SiO2 3.84
P2O5 0.00
TiO2 0.00
Fe2O3 0.00
Al:Si=1.00:17.98
Neut:Acid=1.00:9.06
A:N:A=1.00:0.42:3.84
Expansion: 68.8
It was created by adding silica to the original. It is no longer a good
glass - pitted, blistered, opaque, dull - but it still crazed almost
immediately upon removal from the kiln. The kiln was below 200F when I
opened it.
Wanda
-----Original Message-----From: Ceramic Arts Discussion List
[mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ron Roy
Sent: Thursday, September 12, 2002 12:52 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: COE - need help from glaze gurus
Hi Wanda,
This must have gotten by me when I was away - anyway - anything below
7.0 COE has a good chance of not crazing on many bodies as illustrated
in chapter 5 in our book. What could be the problem in this case is the
accuracy of the materials definitions in your program - send me the
other recipe and I will check them out for you.
If you want to know the COE of any clay body use the glazes in Mastering
Glazes - you will certainly get a better picture of which bodies will
help in this situation.
Any way send me the other recipe - don't hold you breath about this -
potters (as someone else has pointed out) have been trying to solve this
one for centuries. Perhaps changing to a clay body with a higher COE may
be the way to go. Ask you clay supplier if they have any COE info on
their clays.
By the way - the boron in the glaze below is only at 5.2 percent so that
may be worth while - to increase that.
I have recalculated the recipe below adding more boron using frit 3134 -
keep in mind silica lowers expansion - the more frit in the body the
faster the melt - so it means you can get more silica in. The expansion
is lowered but not a lot.
By the way the recipe below only adds to 95 - it that right?
F3110 - 15.0
F 3289 - 27.0
F 3134 - 15.0
Lith Carb - 2.0
EPK - 13.0
Silica - 28.0
Total - 100.0
Ball clay would work better in this - I'm sure it's going to deflocc -
let me know what kinds of ball clay you can get.
RR
>Wanda Holmes writes:
>
>> I am trying to develop a stable alkaline glaze for cone 6 oxidation.
>> The following glaze gives a beautiful clear glass with exactly the
>> color I want with 4% copper carb, but it crazes like crazy
>> immediately upon removal from the kiln.
>>
>> Frit 3110 20
>> EPK 10
>> Silica 27
>> Frit 3289 34
>> Lithium carb 4
>>
>> GlazeChem gives this glaze a COE of 73.5. I've been adding silica to
>> bring down the COE. I've gotten the COE down to as low as 66.7
>> although the glaze has now lost many of its original and desirable
>> properties of color and clarity. It has not, however, lost the
>> crazing property.
>>
>> GlazeChem gives John & Ron's calcium semi-matte a COE of 72.6. I
>> have absolutely no problems with it, on the same claybody fired
>> exactly the same way.
>>
>> Why does one glaze with a higher COE work just fine while another
>> with a much lower COE craze like the dickens? What am I missing?
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
________________________________________________________________________
______
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.
Wanda Holmes on fri 13 sep 02
Ivor, let me see if I understand. Since the glaze will melt at a low
temperature, the silica, whiting, and kaoling will not have a chance to
fully dissolve even though I'm firing to cone 6????? wanda
-----Original Message-----
From: iandol [mailto:iandol@tell.net.au]
Sent: Monday, September 09, 2002 2:07 PM
To: Wanda Holmes
Cc: clayart@LSV.CERAMICS.ORG
Subject: Re: COE - need help from glaze gurus
Looking at what I wrote to you, yes, I do stand by that statement. Even
with the additional input about the missing ingredient I think this is a
glaze which will melt at a low temperature. With those fritted fluxes,
one being an Alkali borate and the other a Barium borate, it seems like
an earthen ware glaze for something like cone 04. Another thing which
disturbs me about this and similar mixtures is the degree to which the
refractory components; Silica, Whiting and Kaolin, will dissolve. They
need either time or heat to accomplish this. If they do not go into
solution then the glaze will be immature and may be prone to crazing.
Definitely an interesting quandary. Best regards, Ivor Lewis
----- Original Message -----
From: "Wanda Holmes"
To: "'Ceramic Arts Discussion List'"
Cc: "'iandol'"
Sent: Monday, 9 September 2002 11:34
Subject: RE: COE - need help from glaze gurus
> Ivor, I made a mistake in my original posting. I left out an
ingredient
> in the recipe. The actual recipe is:
> Frit 3110 20
> EPK 10
> Silica 27
> Frit 3289 34
> Whiting 9
> Lithium carb 4.
>
> With this correction, does your observation about maturation point
still
> hold? If so, what would you do to raise it?
>
> Thanks for your help,
> Wanda
>
> -----Original Message-----
> From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]
On
> Behalf Of iandol
> Sent: Saturday, September 07, 2002 1:30 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: COE - need help from glaze gurus
>
>
> Dear Wanda Holmes,
>
> It is always a puzzle trying to determine why things do not go as
> anticipated, according to the theory or the calculations.
>
> I would make two points which I think are valid.
>
> First is that you can always consider your current clay. Can this be
> changed or altered to alleviate the crazing problem.
>
> The second is that there seem to be no notes in the literature
> suggesting those who intend designing glazes should take pre-emptive
> action to eliminate the problem before it arises.
>
> Specific to your current situation. This seems to be a glaze with a
very
> low maturity point. Perhaps the problem is due to immature clay at
your
> chosen maturing temperature.
>
> It will be interesting to know what the others propose.
>
> Best regards,
>
> Ivor Lewis. Redhill, South Australia
>
>
______________________________________________________________________
__
> ______
> 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.
>
>
David Hewitt on sat 14 sep 02
In message , Ron Roy writes
>Hi John - there is a list in the back of the Hamer book which gives
>relative expansion rates of most oxides we use.
There is indeed a list as you say. It does not actually give figures but
lists the oxides going from High Expansion to Low Expansion with two
notes suggesting the 'gap' between one oxide and the next. Also it does
not say the sauce of this list. I would suspect that it is a combination
of Hamer's experience and some other ceramist's work. In most respects
it reflects Mayer/Havas
>
>I hear some saying do not mix expansion rates from different lists - that
>is right but you can deduce relative expansion by comparing - for instanc=
>e
>-
>
Both Mayer/Havas and Appen give figures for a number of colouring
oxides, but when you look at these they are not all in the same relative
order.
The following table illustrates this.
The figures for Appen are % Mol Linear x10-7/oC
The figures for Mayer/Havas are % Wt. Cubic x 10-7/oC
there are not figures for Hamer but the colouring oxides are listed in
relative expansion from high to low.
Appen Mayer/Havas Hamer
FeO 55 Cr2O3 5.1 Cr2O3
Fe2O3 55
CoO 4.4 CoO
CoO 50
NiO 50 TiO2 4.1
CuO 30 Fe2O3 4.0 Fe2O3
NiO 4.0 NiO
TiO2 30-1.5(%SiO2-50) TiO2
MnO 2.2
SnO2 -45 CuO 2.2 MnO
CuO
FeO 2.0
SnO2 2.0 SnO2
I hope that the tabs come out OK to make this readable.
As you say, the amount of colouring oxides are small so any error would
not be that great. I still think, however, that it is better practice
to use English/Turner figures as they stand together with Appen for any
recipe that you are studying.
I have built in all options into my Glaze Workbook, as also has Matrix.
All too often it would seem to be assumed that there is only one set of
figures for expansion calculations as they are often quoted without
reference and without units. A hobby-horse of mine, as you know, so
please bear with me. I am quite sure that COE calculations can be
extremely useful in indicating the direction of making a change in a
recipe, but I do not consider that any calculated COE figure, regardless
of which ceramist's coefficients you use, to be a precise figure of the
actual COE. Add to this ones experience of which COE numbers fit a given
clay body and you are getting somewhere.
>Say CuO falls between Zinc at 7 and MgO at 4.0 (I'm making these up by th=
>e
>way) then we can assume CuO is about 5.2 - accurate enough because so
>little copper is usually used. Some lists have some of each so it is a wo=
>rk
>around.
>
>In fact Hamer says CuO is the same as MnO - big clue!
>
>After that all one needs to do is construct an experiment to see if coppe=
>r
>increases expansion or lowers it in a glaze (glossy) with an expansion of
>say 5.2. If it does not work then rethink.
>
>There have been comments that some colours seem to affect expansion in wa=
>ys
>we cannot account for - there needs to be some work done in this area - n=
>ot
>rocket science to find out some useful information.
>
>RR
>
>>John,
>>I am interested in finding a list of colorants exp/cont. Does this exis=
>t?
>>
>>Thanks, John Britt
>
>
>Ron Roy
>RR#4
>15084 Little Lake Road
>Brighton, Ontario
>Canada
>K0K 1H0
>Phone: 613-475-9544
>Fax: 613-475-3513
--
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
Autumn Downey on sat 14 sep 02
Hello David,
Thanks for sharing the info and numbers - and provisos for the colouring
oxides.
Just wondering if tin with its low COE and negative number (according to
Appen) would make it a good anti-crazing additive - if it worked with the
intended glaze colour
Tin seems like a very "glaze-friendly material" - except for price.
Autumn Downey
>>
>Both Mayer/Havas and Appen give figures for a number of colouring
>oxides, but when you look at these they are not all in the same relative
>order.
>
>The following table illustrates this.
>The figures for Appen are % Mol Linear x10-7/oC
>The figures for Mayer/Havas are % Wt. Cubic x 10-7/oC
>there are not figures for Hamer but the colouring oxides are listed in
>relative expansion from high to low.
>
>Appen Mayer/Havas Hamer
>FeO 55 Cr2O3 5.1 Cr2O3
>Fe2O3 55
> CoO 4.4 CoO
>CoO 50
>NiO 50 TiO2 4.1
>
>CuO 30 Fe2O3 4.0 Fe2O3
> NiO 4.0 NiO
>TiO2 30-1.5(%SiO2-50) TiO2
> MnO 2.2
>SnO2 -45 CuO 2.2 MnO
> CuO
> FeO 2.0
> SnO2 2.0 SnO2
>
>I hope that the tabs come out OK to make this readable.
>
>As you say, the amount of colouring oxides are small so any error would
>not be that great. I still think, however, that it is better practice
>to use English/Turner figures as they stand together with Appen for any
>recipe that you are studying.
>
>I have built in all options into my Glaze Workbook, as also has Matrix.
>All too often it would seem to be assumed that there is only one set of
>figures for expansion calculations as they are often quoted without
>reference and without units. A hobby-horse of mine, as you know, so
>please bear with me. I am quite sure that COE calculations can be
>extremely useful in indicating the direction of making a change in a
>recipe, but I do not consider that any calculated COE figure, regardless
>of which ceramist's coefficients you use, to be a precise figure of the
>actual COE. Add to this ones experience of which COE numbers fit a given
>clay body and you are getting somewhere.
>
>>Say CuO falls between Zinc at 7 and MgO at 4.0 (I'm making these up by th=
>>e
>>way) then we can assume CuO is about 5.2 - accurate enough because so
>>little copper is usually used. Some lists have some of each so it is a wo=
>>rk
>>around.
>>
>>In fact Hamer says CuO is the same as MnO - big clue!
>>
>>After that all one needs to do is construct an experiment to see if coppe=
>>r
>>increases expansion or lowers it in a glaze (glossy) with an expansion of
>>say 5.2. If it does not work then rethink.
>>
>>There have been comments that some colours seem to affect expansion in wa=
>>ys
>>we cannot account for - there needs to be some work done in this area - n=
>>ot
>>rocket science to find out some useful information.
>>
>>RR
>>
>>>John,
>>>I am interested in finding a list of colorants exp/cont. Does this exis=
>>t?
>>>
>>>Thanks, John Britt
>>
>>
>>Ron Roy
>>RR#4
>>15084 Little Lake Road
>>Brighton, Ontario
>>Canada
>>K0K 1H0
>>Phone: 613-475-9544
>>Fax: 613-475-3513
>
>--
>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
>
>___________________________________________________________________________
___
>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.
>
>
David Hewitt on sun 15 sep 02
Autumn,
Tin oxide is of course an opacifier but if that produces an acceptable
colour etc. then it should also be beneficial in reducing the glaze COE.
All those ceramists who list SnO2 give it a low coefficient, not just
Appen.
David
In message , Autumn Downey writes
>Hello David,
>
>Thanks for sharing the info and numbers - and provisos for the colouring
>oxides.
>
>Just wondering if tin with its low COE and negative number (according to
>Appen) would make it a good anti-crazing additive - if it worked with the
>intended glaze colour
>
>Tin seems like a very "glaze-friendly material" - except for price.
>
>Autumn Downey
>
>
>
>
>
>>>
>>Both Mayer/Havas and Appen give figures for a number of colouring
>>oxides, but when you look at these they are not all in the same relative
>>order.
>>
>>The following table illustrates this.
>>The figures for Appen are % Mol Linear x10-7/oC
>>The figures for Mayer/Havas are % Wt. Cubic x 10-7/oC
>>there are not figures for Hamer but the colouring oxides are listed in
>>relative expansion from high to low.
>>
>>Appen Mayer/Havas Hamer
>>FeO 55 Cr2O3 5.1 Cr2O3
>>Fe2O3 55
>> CoO 4.4 CoO
>>CoO 50
>>NiO 50 TiO2 4.1
>>
>>CuO 30 Fe2O3 4.0 Fe2O3
>> NiO 4.0 NiO
>>TiO2 30-1.5(%SiO2-50) TiO2
>> MnO 2.2
>>SnO2 -45 CuO 2.2 MnO
>> CuO
>> FeO 2.0
>> SnO2 2.0 SnO2
>>
>>I hope that the tabs come out OK to make this readable.
>>
>>As you say, the amount of colouring oxides are small so any error would
>>not be that great. I still think, however, that it is better practice
>>to use English/Turner figures as they stand together with Appen for any
>>recipe that you are studying.
>>
>>I have built in all options into my Glaze Workbook, as also has Matrix.
>>All too often it would seem to be assumed that there is only one set of
>>figures for expansion calculations as they are often quoted without
>>reference and without units. A hobby-horse of mine, as you know, so
>>please bear with me. I am quite sure that COE calculations can be
>>extremely useful in indicating the direction of making a change in a
>>recipe, but I do not consider that any calculated COE figure, regardless
>>of which ceramist's coefficients you use, to be a precise figure of the
>>actual COE. Add to this ones experience of which COE numbers fit a given
>>clay body and you are getting somewhere.
>>
>>>Say CuO falls between Zinc at 7 and MgO at 4.0 (I'm making these up by th=
>>>e
>>>way) then we can assume CuO is about 5.2 - accurate enough because so
>>>little copper is usually used. Some lists have some of each so it is a wo=
>>>rk
>>>around.
>>>
>>>In fact Hamer says CuO is the same as MnO - big clue!
>>>
>>>After that all one needs to do is construct an experiment to see if coppe=
>>>r
>>>increases expansion or lowers it in a glaze (glossy) with an expansion of
>>>say 5.2. If it does not work then rethink.
>>>
>>>There have been comments that some colours seem to affect expansion in wa=
>>>ys
>>>we cannot account for - there needs to be some work done in this area - n=
>>>ot
>>>rocket science to find out some useful information.
>>>
>>>RR
>>>
>>>>John,
>>>>I am interested in finding a list of colorants exp/cont. Does this exis=
>>>t?
>>>>
>>>>Thanks, John Britt
>>>
>>>
>>>Ron Roy
>>>RR#4
>>>15084 Little Lake Road
>>>Brighton, Ontario
>>>Canada
>>>K0K 1H0
>>>Phone: 613-475-9544
>>>Fax: 613-475-3513
>>
>>--
>>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
>>
>>___________________________________________________________________________
>___
>>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.
>>
>>
--
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
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