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coefficients of expansion

updated thu 2 nov 06

 

Earl Brunner on wed 10 feb 99

From what I understand from several of the reference books that I have,
Hamer, Peterson, Rhodes, Parmelee( this ones a heavy read, I sound like
one of my first and second graders,"But where are the pictures?").
Anyway, I digress, If I understand it, the higher the coefficent of
expansion, the more likely to craze? Potassium and Soda are pretty high
on the list for high coefficients? Lowest, Silica? Are there target
coefficients of expansion that would tie to limit formulas, and does
trying to tie them to limit formulas even make sense? Or am I trying
for similar coefficents at say cone 6 as I would at cone 10?
If my glaze calculation software calculates a coefficient of expansion
of 78.1 x 10e-7 per degree C (what ever that means)for example, what
would I expect to be able to infer, if anything?
Help?
Don't laugh, I'm serious even if I am muddled on this one.
Earl Brunner

David Hewitt on thu 11 feb 99


In message , Earl Brunner writes
>----------------------------Original message----------------------------
>From what I understand from several of the reference books that I have,
>Hamer, Peterson, Rhodes, Parmelee( this ones a heavy read, I sound like
>one of my first and second graders,"But where are the pictures?").
>Anyway, I digress, If I understand it, the higher the coefficent of
>expansion, the more likely to craze? Potassium and Soda are pretty high
>on the list for high coefficients? Lowest, Silica? Are there target
>coefficients of expansion that would tie to limit formulas, and does
>trying to tie them to limit formulas even make sense? Or am I trying
>for similar coefficents at say cone 6 as I would at cone 10?
The important thing with coefficients of expansion is how the
coefficient of the glaze relates to that of the clay body. They do not
relate to limit formulae which are concerned primarily with glaze
durability.

>If my glaze calculation software calculates a coefficient of expansion
>of 78.1 x 10e-7 per degree C (what ever that means)for example, what
>would I expect to be able to infer, if anything?
You need to know whose coefficients you are using before answering this.
Different ceramists have over the years produced different coefficients
for the different oxides and the resultant calculations for a glaze can
differ a lot.

For more details on glaze fit, the difference the clay body makes and
the different coefficients, you may wish to look at the following web
site.
http://digitalfire.com/education/people/hewitt.htm
or connect through my own web site and 'Pottery Techniques'
http://www.dhpot.demon.co.uk
>Help?
>Don't laugh, I'm serious even if I am muddled on this one.
>Earl Brunner
>

--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm

Fabienne Cassman on thu 11 feb 99

------------------
Hello Earl,

let me take a crack at it=3B I used to have the same doubts a few months ago
:) I'll stand corrected by the more erudite if I am wrong.

=3Csnip=3E
=3EAnyway, I digress, If I understand it, the higher the coefficent of
=3Eexpansion, the more likely to craze? Potassium and Soda are pretty high
=3Eon the list for high coefficients? Lowest, Silica? Are there target
=3Ecoefficients of expansion that would tie to limit formulas, and does
=3Etrying to tie them to limit formulas even make sense? Or am I trying
=3Efor similar coefficents at say cone 6 as I would at cone 10?
=3EIf my glaze calculation software calculates a coefficient of expansion
=3Eof 78.1 x 10e-7 per degree C (what ever that means)for example, what
=3Ewould I expect to be able to infer, if anything?
=3Csnip=3E

A higher coefficient of expansion (COE) tends to craze, but it would have
to be higher that the COE of the clay body you are using. As far as how
much higher, I still have to figure it out if there is a pattern at all. I
see the clay and the glaze as two entities dancing in unison, never letting
each other go but without holding onto each other too hard either. Like a
waltz :)

Yes, potassium and sodium oxides have high COEs and if used as the only
fluxes in a glaze, the glaze will craze. If I recall correctly they are
also soluble which could also cause leaching (relatively soluble in
feldspar, thus better if introduced in FRIT).

The limits are a yard stick against which you measure how
balanced/safe/durable... your glaze is. They suggest different ranges for
different cones=3B there is a determined amount of each oxide that you can
introduce into the glaze depending on the cone/range. You can make glazes
outside of the predetermined ranges=3B it could yield interesting visual
effects otherwise impossible to make, but the glaze will most likely not be
safe to eat on and have other integrity defects. It doesn't mean that a
glaze made within limits is always safe, e.g., adding a high percentage of
a metal oxide would probably make it unsafe.

To complicate matters, you have to watch the COE while staying within
limits such that the COE is not too high nor too low compared to that of
the clay body. Without software, I can't imagine how long it would take.
It's a painful process when starting, but as time goes by it becomes easier
and I can say that after only a few months, I can only dream of how easy it
will be in a few years :)

A COE of 78.1 x 10e-7 per degree C means that you clay expands 0.00000781
inches (or centimeters) when the temperature moves one degree Celsius.
Pretty small move, but one that could to ruin your day.

I hope this helps,
=A4=BA=B0=60=B0=BA=A4=F8,=B8=B8,=F8=A4=BA=B0=60=B0=BA=A4=F8,=B8=B8,=F8=A4=BA=
=B0=60=B0=BA=A4=F8,=B8=B8,=F8=A4=BA=B0=60=B0=BA=A4=F8,=B8=B8,=F8=A4=BA=B0=60
Fabienne
Yes, I have learned from my mistakes...
I can reproduce them exactly.

Barney Adams on thu 11 feb 99

Hi,
In case Tom Buck has'nt already answered. For a ^6
stoneware he suggests 7.00 + or - 0.02. Porcelein seems
to be a bit lower. As I've been finding and as everyone tells me
test test test.

Barney

Earl Brunner wrote:

> ----------------------------Original message----------------------------
> >From what I understand from several of the reference books that I have,
> Hamer, Peterson, Rhodes, Parmelee( this ones a heavy read, I sound like
> one of my first and second graders,"But where are the pictures?").
> Anyway, I digress, If I understand it, the higher the coefficent of
> expansion, the more likely to craze? Potassium and Soda are pretty high
> on the list for high coefficients? Lowest, Silica? Are there target
> coefficients of expansion that would tie to limit formulas, and does
> trying to tie them to limit formulas even make sense? Or am I trying
> for similar coefficents at say cone 6 as I would at cone 10?
> If my glaze calculation software calculates a coefficient of expansion
> of 78.1 x 10e-7 per degree C (what ever that means)for example, what
> would I expect to be able to infer, if anything?
> Help?
> Don't laugh, I'm serious even if I am muddled on this one.
> Earl Brunner

Ron Roy on thu 11 feb 99

Hi Earl,

We should - when dealing with this subject - in consideration for those who
are just learning - always say expansion/contraction - even better
expansion on heating and contraction on cooling. Both are reversible - they
always return to the same size after heating or cooling if no melting takes
place.

Limit formulas are used for predicting melt and have nothing at all to do
with expansion.

Yes - the higher the expansion of the overall glaze the more likely crazing
will happen - because the glaze - on cooling tries to get smaller than the
clay.

Finding your "magic" number (below which glazes will not craze) is a matter
of testing your glazes on a clay - each clay has it's own unique expansion
- so you have to test each body to get a magic number for each one.

Lets say you have a calculated expansion for a glaze and it's say 7.0 and
that glaze crazes on your clay. Lets say you have another glaze that does
not craze - even after testing for fit - and it's number is 6.0. Now you
know the number you are looking for is between 7 and 6 - you do a line
blend of the two glazes and narrow it down - or just use 6 as your ideal if
there are no shivering or dunting (opposite problem from crazing - glaze
winds up too big at room temp.)

Sounds all very simple - right. Well not quite. Expansion calculation is a
black art and can be misleading - you still have to test - the main value
in calculating expansion is having some idea that you are going in the
right direction. It is not reliable with recrystallized glazes.

So when you say silica has one of the lowest expansions - and you mean
amorphous - in the glaze state - not the crystallized state - you
understand why so many say - if your glaze is crazing just add silica.
That's the simple (least intelligent) answer. If you try to solve it that
way it will change the look of the glaze. The best way is usually a
combination of increasing the low expansion oxides at the expense of the
high expansion oxides. Sounds hard but it's really quite simple if you are
using the calculation to "see" the formula of the fired glaze.

Well OK - it's not as simple as I am making out - there are other factors -
like the effect of some oxides changes with the amount present.

I can say it's not that hard in a way because I can teach others how to do
it in a week. Knowing the effect of all the oxides on a glaze is key to
solving problems - the more you read about that part - the faster you will
get proficient.

If you have questions - you can get me at Mels for the next 4 days - RR

>----------------------------Original message----------------------------
>From what I understand from several of the reference books that I have,
>Hamer, Peterson, Rhodes, Parmelee( this ones a heavy read, I sound like
>one of my first and second graders,"But where are the pictures?").
>Anyway, I digress, If I understand it, the higher the coefficent of
>expansion, the more likely to craze? Potassium and Soda are pretty high
>on the list for high coefficients? Lowest, Silica? Are there target
>coefficients of expansion that would tie to limit formulas, and does
>trying to tie them to limit formulas even make sense? Or am I trying
>for similar coefficents at say cone 6 as I would at cone 10?
>If my glaze calculation software calculates a coefficient of expansion
>of 78.1 x 10e-7 per degree C (what ever that means)for example, what
>would I expect to be able to infer, if anything?
>Help?
>Don't laugh, I'm serious even if I am muddled on this one.
>Earl Brunner

Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849

Web page: http://digitalfire.com/education/people/ronroy.htm

Dale A. Neese on fri 12 feb 99

Hi Ron,
Explanations as explanations go on this site usually create more questions
than they answer. Your transmission of the coefficients, to the person with
inquiry, talks to the desire for knowledge in our profession.
Those seeking more information will benefit immensely attending the series
of discussions and presentations at this years NECEA Conference. Roy, along
with Jonathan Kaplan, Paul Lewing, and other ClayArt subscribers will be
there in person. Listen to the panel discussions, and then ask your question
for the rest of us on the UKY Server. See you in Columbus.
Dale Tex
l Message-----
From: Ron Roy
To: CLAYART@LSV.UKY.EDU
Date: Thursday, February 11, 1999 8:02 PM
Subject: Re: coefficients of expansion


----------------------------Original message----------------------------
Hi Earl,

We should - when dealing with this subject - in consideration for those who
are just learning - always say expansion/contraction - even better
expansion on heating and contraction on cooling. Both are reversible - they
always return to the same size after heating or cooling if no melting takes
place.

Limit formulas are used for predicting melt and have nothing at all to do
with expansion.

Yes - the higher the expansion of the overall glaze the more likely crazing
will happen - because the glaze - on cooling tries to get smaller than the
clay.

Finding your "magic" number (below which glazes will not craze) is a matter
of testing your glazes on a clay - each clay has it's own unique expansion
- so you have to test each body to get a magic number for each one.

Lets say you have a calculated expansion for a glaze and it's say 7.0 and
that glaze crazes on your clay. Lets say you have another glaze that does
not craze - even after testing for fit - and it's number is 6.0. Now you
know the number you are looking for is between 7 and 6 - you do a line
blend of the two glazes and narrow it down - or just use 6 as your ideal if
there are no shivering or dunting (opposite problem from crazing - glaze
winds up too big at room temp.)

Sounds all very simple - right. Well not quite. Expansion calculation is a
black art and can be misleading - you still have to test - the main value
in calculating expansion is having some idea that you are going in the
right direction. It is not reliable with recrystallized glazes.

So when you say silica has one of the lowest expansions - and you mean
amorphous - in the glaze state - not the crystallized state - you
understand why so many say - if your glaze is crazing just add silica.
That's the simple (least intelligent) answer. If you try to solve it that
way it will change the look of the glaze. The best way is usually a
combination of increasing the low expansion oxides at the expense of the
high expansion oxides. Sounds hard but it's really quite simple if you are
using the calculation to "see" the formula of the fired glaze.

Well OK - it's not as simple as I am making out - there are other factors -
like the effect of some oxides changes with the amount present.

I can say it's not that hard in a way because I can teach others how to do
it in a week. Knowing the effect of all the oxides on a glaze is key to
solving problems - the more you read about that part - the faster you will
get proficient.

If you have questions - you can get me at Mels for the next 4 days - RR

>----------------------------Original message----------------------------
>From what I understand from several of the reference books that I have,
>Hamer, Peterson, Rhodes, Parmelee( this ones a heavy read, I sound like
>one of my first and second graders,"But where are the pictures?").
>Anyway, I digress, If I understand it, the higher the coefficent of
>expansion, the more likely to craze? Potassium and Soda are pretty high
>on the list for high coefficients? Lowest, Silica? Are there target
>coefficients of expansion that would tie to limit formulas, and does
>trying to tie them to limit formulas even make sense? Or am I trying
>for similar coefficents at say cone 6 as I would at cone 10?
>If my glaze calculation software calculates a coefficient of expansion
>of 78.1 x 10e-7 per degree C (what ever that means)for example, what
>would I expect to be able to infer, if anything?
>Help?
>Don't laugh, I'm serious even if I am muddled on this one.
>Earl Brunner

Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849

Web page: http://digitalfire.com/education/people/ronroy.htm

Ron Roy on wed 17 feb 99

I just checked this out and compared my scale with the numbers in Insight
and I get 7.13 so certainly 7.0 is going to work with most glazes on many
cone 6 clays - well certainly on all the Tuckers bodies - I know cause I
have dilatometer charts for all of those clays and have measured enough
cone 6 boron glazes to be sure enough to say so - now keep this in mind -
boron glazes are more tolerant than other glazes in this respect -
particularly when the boron content is under 12%.

Again I should caution - calculated expansion numbers simply do not
translate into the real numbers generated by actual measurement.

Just in case there is anybody interested in the why - it's difficult to
explain here but if I could show you a composite chart of clays and glazes
you would - it has to do with - when the glaze becomes "set" (cannot make
any adjustment to the contraction of the clay during cooling.) There is no
tension above that point because the glazes are still soft and can adjust.

Anyway this all is happening during the "transition stage" of the cooling
(or re melting) of the glaze. This is the stage that glass workers must
anneal through because the changes are quite fast compared to the other
stages.............good reason not to open your kiln too soon by the way.

Every glaze has a different transition stage - in duration and start and
end temperature. Every clay has a different expansion/contraction rate and
a different crystalline quartz inversion depending on the amount of free
quartz still uncombined in the fired body.

So - as you can see - it is no mean feat to try to generalize about
clay/glazes fit - especially at the higher temperatures (like cone 10)
where you also have the added complication of possible cristobalite
inversions adding to the impossibility of predicting fit by calculation.

Barney's caution about testing for workable fits is well taken - and thanks
for the help this last weekend Barney - you did good! - well, excellent
actually.

RR

>----------------------------Original message----------------------------
>Hi,
>In case Tom Buck has'nt already answered. For a ^6
>stoneware he suggests 7.00 + or - 0.02. Porcelein seems
>to be a bit lower. As I've been finding and as everyone tells me
>test test test.
>
>Barney
>
>Earl Brunner wrote:

Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849

Web page: http://digitalfire.com/education/people/ronroy.htm

Tom Buck on thu 18 feb 99

As an added footnote to Ron's view of COE's from a claybody's viewpoint
(and Ron has for decades designed bodies so he knows):
Glaze calc programs are only as accurate as their data allows, and
Oxide coefficients of thermal expansion, determined by acutal experiment
over the years, are rough averages of many experiments. So when the
individual COEs are summed to yield an estimate of the glaze's COE, please
do not expect high precision. If the number is of a certain value, then
you stand a reasonable chance of avoiding crazing or shivering on your
claybody. As the value varies from this midpoint signalling a good fit,
then you head towards trouble.
But as Ron clearly notes, all the effort that goes into getting
the pot ready for the kiln, and the actual firing of the kiln itself, all
this effort goes for nought if you do it badly. You should ensure the
process is done to a regular standard, and stay that way as you test new
glaze recipes.
Good tests. Tom.

Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).

David Hewitt on sun 29 oct 06


May I make a plea for COE figures to be fully defined. In to-day's
digest one sees the following figures quoted in three different
postings.
66.47
420.74
'...7.59 On the clay bodies I use, this would definitely craze.'

I am sure that all are correct in their way, but as pieces of
information they are, at least, confusing for the reader.

For the first recipe, for example, using CeramDat the figures come out
as follows:-

English & Turner 2.936 x10-6 / oC Linear
or
Mclindon 6.718 x10-6 /oC Linear
or
Appen 5.313 x10-6 /oC Linear

I would suspect, therefore, that the first recipe below was calculated
using McLindon but with x10-7

All the glaze programs that I know tell you which Ceramists figures are
used for the calculation and the units, so it would not be much trouble
for them to be quoted. It would, however, make it much easier for
readers to appreciate what is being said.

I am not suggesting that we should all use the same Ceramists
coefficients or the same units, but that we do say which we are using.

David

In message , Paulette Carr writes
>Alistair,
>
>
>Recipe:
>Frit 3195 62
>Frit 3134 9.5
>Silica 9.5
>Kaolin 19
>
>Formula
>
>Na2O .330
>K2O .003
>MgO .010
>Cao .650
>Al2O3 .603
>B2O 1.019
>SiO2 3.665
>Coefficient of Expansion 66.47
Subject: lower glaze temp to cone 6
From: Ron Roy
Date: Sat, 28 Oct 2006 12:49:05 -0500

Troy Black @ cone 6 (untested)
-----------------
CUSTER SPAR......... 13.00
F3278............... 16.00
SILICA.............. 14.50
DOLOMITE............ 4.00
TALC................ 19.50
OM-4................ 27.50
WHITING............. 5.50
=RED IRON OX......... 3.00
+cobalt ox........... 3.00
=MnO2................ 2.00
+chorme ox .......... 1.00
----------
109.00
Seger formula
------------------
*CaO........ .35 7.44%
MnO2....... .06 2.11%
*MgO........ .47 7.08%
*K2O........ .05 1.65%
*Na2O....... .13 3.11%
Fe2O3...... .06 3.52%
TIO2....... .01 .34%
B2O3....... .14 3.59%
AL2O3...... .27 10.40%
SiO2....... 2.69 60.75%

RATIO 9.93 (original is 9.91)
EXPAN 420.74 (original is 471.58)
WEIGHT 265.99
>
> Bate's Clear,
> Clear,
> Glossy,
> 6,
> ,
> ,
> Works nicely over other glazes,
> ,
> Feldspar--Kona F4 ,3500,
> Flint ,2200,
> Gerstley Borate--1999 ,1800,
> Kaolin--EPK ,1000,
> Strontium Carbonate ,800,
> Whiting ,800,
>

Donna,

It depends a lot on what body you're using. Insight gives the
expansion of this glaze as: 7.59. On the clay bodies I use, this
would definitely craze. To fix this recipe for my bodies, and ONLY by
adding silica, I'd have to more more or less triple the amount of
Flint. But then ... it's not matte, anymore, is it? Magnesium can
really help reduce thermal expansion (ie., crazing). Maybe some line
tests with dolomite and/or talc would be helpful.

Cheers,

Tim

--
David Hewitt

Web:- http://www.dhpot.demon.co.uk

Paulette Carr on sun 29 oct 06


David,

I clearly see your point, and it is well taken. The different values
are very confusing. Since, however, I personally provided no
recipe, and no COE numbers in my post, and merely reflected on what
another post had mentioned (which I did understand, because I am
familiar with the glaze calculation program that was used to produce
the number), I did not feel it necessary to give dimensions (units)
to numbers I did not mention. The previous posts, containing recipes
and COE values were appended to my post, because I was referencing
the original posts that prompted me to join the conversation. When I
do provide a COE value, it is one produced by Insight, using the
Insight COE set with dimensions of 10-6 in/in/ degree C - linear,
unless I reference it otherwise. I have a choice of many sets
including Insight traditional values, Ron Roy's, and E & T (English
and Turner), West and Gerrow, Windelmann and Schott, Eppler and
Eppler. This is built into the Insight glaze calculation program.
I do not have sets for McLindon, or Appen, but I suppose that I could
find and enter them. I use the Insight numbers for myself, not for
their absolute values, but to determine directions or trends, and
now their values mean something to me, along with the analysis of the
recipe.

When I correspond with Ron Roy, I do try to use his values, but
correlate them to the Insight set that I commonly use. From now on,
whenever I do post, I will reference which COE set I am using so that
as many people as possible can understand what I am saying (which is
very important to me). It may be a good idea to set a standard or
even common definition for COE, for communication purposes, and maybe
this is the place to discuss it. Which would you choose and why???

Just as a point of information for program developers, my choice of
glaze calculation programs is determined by my computer - a Mac with
Mac operating system. Once familiar with the program(s), I have no
reason to switch... I have tried the virtual PC program, spent lots
of money, and had little success getting one non-native program to
run smoothly. I will always opt for a program that is native to my
operating system and functions well on my machine.

Thank you for bringing this to my attention.

My best,
Paulette Carr

Paulette Carr Studio
Member/Potters Council
St. Louis, MO

On Oct 29, 2006, at 2:36 PM, David Hewitt wrote:

> May I make a plea for COE figures to be fully defined. In to-day's
> digest one sees the following figures quoted in three different
> postings.
> 66.47
> 420.74
> '...7.59 On the clay bodies I use, this would definitely craze.'
>
> I am sure that all are correct in their way, but as pieces of
> information they are, at least, confusing for the reader.
>
> For the first recipe, for example, using CeramDat the figures come out
> as follows:-
>
> English & Turner 2.936 x10-6 / oC Linear
> or
> Mclindon 6.718 x10-6 /oC Linear
> or
> Appen 5.313 x10-6 /oC Linear
>
> I would suspect, therefore, that the first recipe below was calculated
> using McLindon but with x10-7
>
> All the glaze programs that I know tell you which Ceramists figures
> are
> used for the calculation and the units, so it would not be much
> trouble
> for them to be quoted. It would, however, make it much easier for
> readers to appreciate what is being said.
>
> I am not suggesting that we should all use the same Ceramists
> coefficients or the same units, but that we do say which we are using.
>
> David
>
> In message , Paulette Carr writes
>> Alistair,
>>
>>
>> Recipe:
>> Frit 3195 62
>> Frit 3134 9.5
>> Silica 9.5
>> Kaolin 19
>>
>> Formula
>>
>> Na2O .330
>> K2O .003
>> MgO .010
>> Cao .650
>> Al2O3 .603
>> B2O 1.019
>> SiO2 3.665
>> Coefficient of Expansion 66.47
> Subject: lower glaze temp to cone 6
> From: Ron Roy
> Date: Sat, 28 Oct 2006 12:49:05 -0500
>
> Troy Black @ cone 6 (untested)
> -----------------
> CUSTER SPAR......... 13.00
> F3278............... 16.00
> SILICA.............. 14.50
> DOLOMITE............ 4.00
> TALC................ 19.50
> OM-4................ 27.50
> WHITING............. 5.50
> =RED IRON OX......... 3.00
> +cobalt ox........... 3.00
> =MnO2................ 2.00
> +chorme ox .......... 1.00
> ----------
> 109.00
> Seger formula
> ------------------
> *CaO........ .35 7.44%
> MnO2....... .06 2.11%
> *MgO........ .47 7.08%
> *K2O........ .05 1.65%
> *Na2O....... .13 3.11%
> Fe2O3...... .06 3.52%
> TIO2....... .01 .34%
> B2O3....... .14 3.59%
> AL2O3...... .27 10.40%
> SiO2....... 2.69 60.75%
>
> RATIO 9.93 (original is 9.91)
> EXPAN 420.74 (original is 471.58)
> WEIGHT 265.99
>>
>> Bate's Clear,
>> Clear,
>> Glossy,
>> 6,
>> ,
>> ,
>> Works nicely over other glazes,
>> ,
>> Feldspar--Kona F4 ,3500,
>> Flint ,2200,
>> Gerstley Borate--1999 ,1800,
>> Kaolin--EPK ,1000,
>> Strontium Carbonate ,800,
>> Whiting ,800,
>>
>
> Donna,
>
> It depends a lot on what body you're using. Insight gives the
> expansion of this glaze as: 7.59. On the clay bodies I use, this
> would definitely craze. To fix this recipe for my bodies, and ONLY by
> adding silica, I'd have to more more or less triple the amount of
> Flint. But then ... it's not matte, anymore, is it? Magnesium can
> really help reduce thermal expansion (ie., crazing). Maybe some line
> tests with dolomite and/or talc would be helpful.
>
> Cheers,
>
> Tim
>
> --
> David Hewitt
>
> Web:- http://www.dhpot.demon.co.uk
>

Timothy Joko-Veltman on sun 29 oct 06


On 10/29/06, Paulette Carr wrote:
> David,
>
> I clearly see your point, and it is well taken. The different values
> are very confusing. Since, however, I personally provided no
> recipe, and no COE numbers in my post, and merely reflected on what
> another post had mentioned (which I did understand, because I am
> familiar with the glaze calculation program that was used to produce
> the number), I did not feel it necessary to give dimensions (units)
> to numbers I did not mention. The previous posts, containing recipes
> and COE values were appended to my post, because I was referencing
> the original posts that prompted me to join the conversation. When I
> do provide a COE value, it is one produced by Insight, using the
> Insight COE set with dimensions of 10-6 in/in/ degree C - linear,
> unless I reference it otherwise. I have a choice of many sets
> including Insight traditional values, Ron Roy's, and E & T (English
> and Turner), West and Gerrow, Windelmann and Schott, Eppler and
> Eppler. This is built into the Insight glaze calculation program.
> I do not have sets for McLindon, or Appen, but I suppose that I could
> find and enter them. I use the Insight numbers for myself, not for
> their absolute values, but to determine directions or trends, and
> now their values mean something to me, along with the analysis of the
> recipe.
>

I also see your point, David ... and also use Insight, which is why I
mentioned that the number came from Insight. Of course I could have
been more explicit, especially considering that, as Paulette says,
Insight offers different COE numbers. In the future, I will make a
point of it.

Looking back, maybe I should have left the numbers out, because that's
not what I was trying to get across. Will definitely be more careful
next time.

Tim

David Hewitt on mon 30 oct 06


In message <16DF34B7-FBA8-42CE-AFF9-93FA17E3AE50@SBCGLOBAL.NET>,
Paulette Carr writes
>
>When I correspond with Ron Roy, I do try to use his values, but
>correlate them to the Insight set that I commonly use. From now on,
>whenever I do post, I will reference which COE set I am using so that
>as many people as possible can understand what I am saying (which is
>very important to me). It may be a good idea to set a standard or even
>common definition for COE, for communication purposes, and maybe this
>is the place to discuss it. Which would you choose and why???
>
There is no one right answer but if I may, may I ask you to look at my
web site:-
http://www.dhpot.demon.co.uk
and go to Pottery Techniques / Calculating Crazing, and on that page
select 'Which set of coefficients to use'

Personally I use English & Turner x10-6 /oC Linear

If you wish to read more of this article you can better judge how this
conclusion was arrived at.

This article is included in the booklet 'Understanding your glaze
Tests', details of which are include on my website under Glaze Recipe
Calculations.

David
--
David Hewitt

Web:- http://www.dhpot.demon.co.uk

Paulette Carr on mon 30 oct 06


On Oct 30, 2006, at 4:26 AM, David Hewitt wrote:

> In message <16DF34B7-FBA8-42CE-AFF9-93FA17E3AE50@SBCGLOBAL.NET>,
> Paulette Carr writes
>>
>> When I correspond with Ron Roy, I do try to use his values, but
>> correlate them to the Insight set that I commonly use. From now
>> on, whenever I do post, I will reference which COE set I am using
>> so that as many people as possible can understand what I am saying
>> (which is very important to me). It may be a good idea to set a
>> standard or even common definition for COE, for communication
>> purposes, and maybe this is the place to discuss it. Which would
>> you choose and why???
>>
> There is no one right answer but if I may, may I ask you to look at
> my web site:-
> http://www.dhpot.demon.co.uk
> and go to Pottery Techniques / Calculating Crazing, and on that
> page select 'Which set of coefficients to use'
>
> Personally I use English & Turner x10-6 /oC Linear
>
> If you wish to read more of this article you can better judge how
> this conclusion was arrived at.
>
> This article is included in the booklet 'Understanding your glaze
> Tests', details of which are include on my website under Glaze
> Recipe Calculations.
>
> David
> --
> David Hewitt
>
> Web:- http://www.dhpot.demon.co.uk
>


David,

I have checked your website and read your article. The dimensions
that you list for English & Turner have dimensions of 10-8 /degree C -
linear. Insight uses 10-7 /degree C - linear, and you just told me
that you are using 10-6 /degree C Linear. I know that I can just
divide my number by 10 to get yours, but why are you using this
unit? Is this the unofficial standard? I will be glad to report any
COE values, in several formats, as a function of the set with which
they are associated, always providing their associated units.
Hopefully, that will alleviate the confusion.

I will just have to learn a new set of numbers, but will need to link
them back to the Insight COE set with which I am most familiar.
Great article, and I have printed it and put it into my glaze
literature notebook.

Ron's idea to have a comparative chart would be a great idea!!!

My best,
Paulette

Paulette Carr Studio
Member/Potters Council
St. Louis, MO

David Hewitt on mon 30 oct 06


In message ,
Paulette Carr writes
Paulette

I think you must be referring to Table 2. In this Table I am quoting the
coefficients as given in the source document. In the case of English &
Turner it was Ceramics Handbook where they quoted the figures as x10-8

Later in the article you will see that I use x10-6 by just moving the
decimal point. This is not an official standard but I find that it is
the most commonly used.

I do not wish to suggest that everyone should use the same as I do, but
that for clarity it is very useful if you at least say the units being
used. Apart from the placing of the decimal point one also needs to be
sure that figure is linear not % or cubic, but more importantly ,whose
coefficients you are using.

I hope that this helps.

David


>>
>
>
>David,
>
>I have checked your website and read your article. The dimensions
>that you list for English & Turner have dimensions of 10-8 /degree C -
>linear. Insight uses 10-7 /degree C - linear, and you just told me
>that you are using 10-6 /degree C Linear. I know that I can just
>divide my number by 10 to get yours, but why are you using this unit?
>Is this the unofficial standard? I will be glad to report any COE
>values, in several formats, as a function of the set with which they
>are associated, always providing their associated units. Hopefully,
>that will alleviate the confusion.
>
>I will just have to learn a new set of numbers, but will need to link
>them back to the Insight COE set with which I am most familiar.
>Great article, and I have printed it and put it into my glaze
>literature notebook.
>
>Ron's idea to have a comparative chart would be a great idea!!!
>
>My best,
>Paulette
>
>Paulette Carr Studio
>Member/Potters Council
>St. Louis, MO

--
David Hewitt

Web:- http://www.dhpot.demon.co.uk

Edouard Bastarache Inc. on mon 30 oct 06


Hello David,

do you know the method used by Chris Hogg in his
programme,
"Glaze4"?


Later,



Edouard Bastarache
Le Franšais Volant
The Flying Frenchman

Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.pshcanada.com/Toxicology.htm
http://www.flickr.com/photos/30058682@N00/
www.thepottersshop.blogspot.com

David Hewitt on tue 31 oct 06


Edouard,

No, I do not know the method used by Chris Hogg.

For some reason my copy of this program, which is a DOS program doesn't
seem to run on my Windows XP so I cannot open it to have a look.

Obviously you had a reason for asking this. May I ask what it was.

David

In message , Edouard Bastarache Inc. writes
>Hello David,
>
>do you know the method used by Chris Hogg in his
>programme,
>"Glaze4"?
>
>
>Later,
>
>
>
>Edouard Bastarache
>Le Franšais Volant
>The Flying Frenchman
>
>Sorel-Tracy
>Quebec
>edouardb@sorel-tracy.qc.ca
>www.sorel-tracy.qc.ca/~edouardb/Welcome.html
>http://perso.wanadoo.fr/smart2000/index.htm
>http://www.pshcanada.com/Toxicology.htm
>http://www.flickr.com/photos/30058682@N00/
>www.thepottersshop.blogspot.com

--
David Hewitt

Web:- http://www.dhpot.demon.co.uk

Edouard Bastarache Inc. on wed 1 nov 06


Hello David,

Smart.Conseil and Ipublished on my Flickr site the
results of
theoritical calculations on different parameters
of the
behaviour of glazes :

http://www.flickr.com/photos/potier/page3/

My results using GlazeChem are very close to the
results
obtained using Winkelmann's method :

http://www.flickr.com/photos/potier/47768428/

Since you have discussed expansion on your site,
and since I used Chris Hogg's program sometimes,
I was wondering if you knew the method used by
Mr. Hogg.

I recently translated an article by Smart on
crazing
that will be uploaded soon. then following is in
French :

http://perso.orange.fr/smart2000/tressaillage.htm


Later,



Edouard Bastarache
Le Franšais Volant
The Flying Frenchman

Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.pshcanada.com/Toxicology.htm
http://www.flickr.com/photos/30058682@N00/
www.thepottersshop.blogspot.com